# A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects

Noemí Pinilla-Alonso, Rosario Brunetto, Mário de Prá, Bryan Holler, Elsa Hénault, Ana Carolina de Souza Feliciano, Vania Lorenzi, Yvonne Pendleton, Dale Cruikshank, Thomas Müller, et al.

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Noemí Pinilla-Alonso, Rosario Brunetto, Mário de Prá, Bryan Holler, Elsa Hénault, et al. A JWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects. Nature Astronomy, 2024, 9 (2), pp.230-244. 10.1038/s41550-024-02433-2. hal-04961629

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# AJWST/DiSCo-TNOs portrait of the primordial Solar System through its trans-Neptunian objects

Received: 31 October 2023

Accepted: 4 November 2024

Published online: 19 December 2024

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A list of authors and their affiliations appears at the end of the paper

The detection of molecules on the coldest and outermost objects in our Solar System has long been limited by the terrestrial atmosphere and sensitivity of the available instrumentation. However, near-infrared observations by the James Webb Space Telescope have provided an unprecedented view of the molecular diversity on the surfaces of trans-Neptunian objects (TNOs). Using the low spectral resolution PRISM mode on the near-infrared spectrograph as part of the Cycle 1 large programme, 'Discovering the Surface Composition of trans-Neptunian objects', we report the detection of several molecular ices throughout the TNO population, including H₂O, CO₂, ¹³CO₂, CO, CH₃OH and complex molecules and refractory materials containing aliphatic C-H, C≡N, O-H and N-H bonds. As a result of the imprint that these molecules leave on the spectra, three main compositional groups consistently emerge from multiple independent cluster analyses. Our results unlock the long-standing question of the interpretation of colour diversity, providing the much-needed compositional information. The marked separation of the three spectral clusters reveals sharp variations in the surface molecular constituents. The C/O and (CH + NH)/(C + O) ratios on the surface of TNOs are the primary indicators of the spectral differences among the three TNO compositional groups observed. We propose that these objects are fossil remnants of icy planetesimals, and that the three compositional groups provide a picture of the ice retention lines in the Solar System that likely occurred in the outer protoplanetary disk, possibly just before a major planetary migration.

The outer region of the Solar System hosts a vast population of small bodies orbiting beyond Neptune, known as trans-Neptunian objects (TNOs). These objects formed during the early epochs of planetesimal accretion at various heliocentric distances. In their early stages, TNOs inherited their initial bulk composition from specific regions of the protoplanetary disk (PPD) where they formed. After formation, multiple processes could have altered the molecular inventory of each TNO, such as planetary migration, irradiation, volatile retention and collisions¹⁻⁵. The orbital reorganization of TNOs caused

by planetary migrations adds complexity to tracing them back to specific formation locations using orbital evolution calculations⁶. Notably, some subpopulations are known to have specific formation regions (for example, TNOs coming from the Oort cloud were formed among the giant planets, cold classical TNOs formed in the outer parts of the disk). These populations are crucial for translating compositional information into constraints on models of their formation and dynamical evolution. Therefore, understanding the surface composition of TNOs is essential for better understanding

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e-mail: npinilla@ucf.edu
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**Fig. 1 | Physical and orbital parameters of the DiSCo sample of TNOs.** See also Extended Data Table 2. a, The visible spectral slope $S' [%/0.1 µm]$ relative to the diameter $D$ (km) ± the standard deviation. b, The visible geometric albedo $ρ_v$ relative to the diameter $D$ (km). c, The eccentricity relative to the semi-major axis (au). d, The inclination (°) relative to the semi-major axis (au). Error bars, as taken from the original papers, are included in Extended Data Table 2. The

different symbols represent their surface composition as found in the three clusters presented in Figs. 2 and 3. The two panels at the bottom include the locations of the 3:2, 5:2 and 7:2 mean-motion resonances with Neptune and the curves corresponding to perihelion distance of 30 and 35 au. The two empty circles in the bottom right panel represent two objects with orbital parameters outside the axis limits, as included in the figure.

the formation of the Solar System and the processes that have shaped it over the last 4.5 billion years.

Because of their large heliocentric distances (30 au ≤ *r* ≤ 100 au) and faintness, measuring the surface molecular composition of most TNOs via remote sensing from ground-based observatories is very challenging. Spectrophotometric observations in the visible and near infrared (NIR) (λ < 2 µm) have provided a comprehensive view of the colour diversity in the TNO population, but attempts to interpret these results in terms of surface compositions have been inconclusive<sup>7–11</sup>. Spectroscopic observations of TNOs have proven to be more successful in establishing water ice and reddening agents (likely complex organics and silicates) as the main surface components<sup>12</sup>. However, these ground-based observations are limited by the attenuating effects of the terrestrial atmosphere. Therefore, spectroscopy from a sensitive infrared (IR) telescope in space is necessary to substantially advance our understanding of these objects<sup>13</sup>.

Spectroscopy using the James Webb Space Telescope (JWST) provides a new and unique opportunity to search for ices in the NIR, particularly between 2 and 5 µm, where most of the expected molecules have their strongest absorption bands. JWST spectroscopy of dense molecular clouds and PPDs also enables the detection of several molecular species, the most abundant being H₂O, CO and CO₂ (and their isotopologues ¹³CO and ¹³CO₂), CH₃OH, NH₃ and NH₄⁺, CH₄, OCN⁻, OCS,

H₂S, HCN, SO₂ and possibly silicates and organics¹⁴. Spacecraft and remote sensing spectroscopic studies of molecules emitted by cometary activity also show a rich molecular diversity¹⁵,¹⁶, often compared to the composition of molecular clouds and disks. Additionally, JWST observations of active Centaurs, small bodies with an origin in the trans-Neptunian belt, have succeeded in detecting the gas and solid phases of a diverse collection of volatile ices, such as CO₂, CH₄, CO, H₂O₂, C₂H₆, OCS and CO₃ (refs. 17,18). These findings confirm expectations for JWST as the most powerful tool to deepen our knowledge of the surface composition of TNOs.

Here we reveal the three main spectral groups of TNOs, which correspond to different surface compositions that were determined using several spectral features of ices and complex organics. The distribution of these classes in terms of dynamical and physical parameters offers new insights into the formation and early evolution of the outer Solar System, suggesting that the trans-Neptunian population provides a snapshot of the icy planetesimals in the PPD before a major planetary migration.

## Results

We carried out observations of 54 TNOs and five Centaurs as part of the large JWST Cycle 1 General Observers programme (2418) 'Discovering the Surface Compositions of trans-Neptunian Objects' (DiSCo-TNOs;
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**Fig. 2 | Results of the PCA and k-means clustering technique.** The first two components of the PCA of the DiSCo dataset show the locations of the three main spectral groups detected by independent *k*-means clustering. Data points are coloured according to the *k*-means rather than any principal component cut-offs, providing additional confirmation of the detection of the clusters (see details in Methods). The spectral difference between the bowls and the other two clusters was stronger than the difference between the cliffs and double dips (see also Supplementary Fig. 1b). Each TNO was labelled by its observation ID (Table 1). Error bars estimated using slightly different normalizations (at 2.58, 2.6 and 2.62 µm) are all smaller than 0.18 for both PC1 and PC2, which are smaller than the size of the points. The colours and shapes of the symbols are the same as in Fig. 1.

Extended Data Table 1)¹⁹. We exclude Centaurs in the rest of this paper because their surfaces can be altered by present or past cometary activity²⁰. The sample contains objects spanning the diversity of the TNO population in terms of size, visible colours, geometric albedo and dynamical properties (Fig. 1 and Extended Data Table 2) and excludes the volatile-rich dwarf planets, which are distinct because of their size, surface composition and geochemical processes. The observations used the integral field unit (IFU) and the PRISM mode of the near-infrared spectrograph (NIRSpec), which provides continuous wavelength coverage from 0.6 to 5.3 µm with a spectral resolving power ranging from 30 to 300 (ref. 21). The raw uncalibrated data were processed locally using the JWST calibration pipeline, and the spectra were extracted using a custom point-spread function (PSF) fitting procedure (Methods). We present the full collection of reflectance spectra derived from the DiSCo-TNO data in Extended Data Figs. 1–4.

## Spectral classification

To probe for distinct spectral groups within the DiSCo-TNO dataset that were suggested by visual inspection, we applied three clustering techniques²² (*k*-means clustering, hierarchical clustering and principal component analysis (PCA)) to our reflectance spectra. All three techniques consistently indicated the existence of three distinct groups within the TNO population (Fig. 2 and Extended Data Fig. 5). Figure 3 shows the median of the individual spectra within each group, as well as the median absolute deviation, which is a representation of the spectral dispersion within each group. Substantial and systematic spectral differences were observed between the three groups, which we refer to by the names ‘bowl’, ‘double dip’ and ‘cliff’, based on the shape of the large 3-µm absorption band (Fig. 3). The main species that we detected (see ‘Spectral attribution’ in Methods and Extended Data Table 3) were H₂O, CO₂ (and its isotopologue ¹³CO₂), CO, CH₃OH and complex organics and

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**Fig. 3 | Representative spectra of each compositional class of TNOs.** The coloured solid lines correspond to the median of the spectra in each of the compositional groups detected in the trans-Neptunian population following the same colour code as in the rest of the paper. The coloured shaded region corresponding to the ± median absolute deviation (MAD) represents the diversity in each group. The grey boxes highlight the detections corresponding to N-H-, C-H- and O-H-bearing materials and aliphatic organics; their limits do not represent any physical measurable. Tentative or unassigned absorptions are shown with a dotted black line (see Extended Data Table 3 for details).

molecules containing aliphatic C-H, C=N, O-H and N-H bonds. The spectral features attributed to these molecules are labelled in Fig. 3.

The bowl-type spectra (25% of the DiSCo sample) are dominated by characteristic water ice absorptions at 1.5, 2.0 and 3.0 µm, including a broad combination band extending from 3.9 to 4.9 µm (Fig. 3 and Extended Data Fig. 6a,b). The deep absorption at 3 µm has a Gaussian-like shape with a similarly high reflectance at the right and left edges. All bowl-type objects clearly show the signature of crystalline water ice at 3.1 µm (Fresnel reflection peak; Extended Data Fig. 6b), whereas the characteristic 1.65-µm band needs modelling for confirmation. We detected the fundamental asymmetric stretching band of CO₂ at 4.27 µm. The bowl TNOs do not show clear aliphatic CH²³ or methanol²⁴ bands but do show a subtle break in the spectral slope at the 3.35-µm band that could be caused by those species. If present, such organics could also contribute to the reddish slope of the continuum
<table><caption>Table 1 | Spectral group, absorption band areas (in µm) and spectral clustering (PCA and k-means) parameters for DiSco-TNOs</caption><thead><tr><th>Number</th><th>Provisional designation</th><th>Name</th><th>Observation ID</th><th>Group</th><th>CH<sub>3</sub>OH</th><th>CO<sub>2</sub></th><th>Aliphatic CH</th><th>H<sub>2</sub>O Fresnel</th><th>PC1</th><th>PC2</th><th>PC3</th><th>Silhouette coefficients</th></tr></thead><tbody><tr><td>48639</td><td>1995TL8</td><td></td><td>39</td><td>Cliff</td><td>0.00485</td><td>0.00234</td><td>0.02762</td><td>-0.00044</td><td>6.63</td><td>1.88</td><td>-1.20</td><td>0.664</td></tr><tr><td>15874</td><td>1996TL66</td><td></td><td>34</td><td>Bowl</td><td>0.00004</td><td>-0.00072</td><td>-0.00034</td><td>0.01175</td><td>-3.98</td><td>1.61</td><td>3.04</td><td>0.603</td></tr><tr><td>79360</td><td>1997CS29</td><td>Sila-Nunam</td><td>43</td><td>Cliff</td><td>0.00120</td><td>0.00076</td><td>0.01683</td><td>0.00012</td><td>2.31</td><td>0.09</td><td>0.36</td><td>0.578</td></tr><tr><td>52872</td><td>1998SG35</td><td>Okyrhoe</td><td>28</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>35671</td><td>1998SN165</td><td></td><td>32</td><td>Bowl</td><td>-0.00021</td><td>0.00004</td><td>-0.00364</td><td>0.00750</td><td>-5.28</td><td>1.61</td><td>-1.05</td><td>0.644</td></tr><tr><td>26375</td><td>1999DE9</td><td></td><td>21</td><td>Double dip</td><td>0.00057</td><td>0.00378</td><td>0.01440</td><td>0.00023</td><td>-1.87</td><td>-2.70</td><td>0.02</td><td>0.667</td></tr><tr><td>44594</td><td>1999OX3</td><td></td><td>104</td><td>Cliff</td><td>0.00186</td><td>0.00002</td><td>0.01661</td><td>0.00001</td><td>4.59</td><td>0.74</td><td>0.66</td><td>0.671</td></tr><tr><td>66652</td><td>1999RZ253</td><td>Borasisi</td><td>56</td><td>Cliff</td><td>0.00073</td><td>0.00089</td><td>0.01126</td><td>-0.00101</td><td>4.32</td><td>0.53</td><td>0.56</td><td>0.659</td></tr><tr><td>47171</td><td>1999TC36</td><td>Lempo</td><td>6</td><td>Cliff</td><td>0.00090</td><td>0.00023</td><td>0.01596</td><td>-0.00102</td><td>3.11</td><td>0.84</td><td>-0.16</td><td>0.643</td></tr><tr><td>38628</td><td>2000EB173</td><td>Huya</td><td>3</td><td>Double dip</td><td>0.00133</td><td>0.00031</td><td>0.01589</td><td>0.00100</td><td>0.19</td><td>0.06</td><td>1.24</td><td>0.577</td></tr><tr><td>138537</td><td>2000OK67</td><td></td><td>51</td><td>Double dip</td><td>0.00182</td><td>0.00333</td><td>0.00281</td><td>0.00070</td><td>0.46</td><td>-1.84</td><td>-0.42</td><td>0.628</td></tr><tr><td>82158</td><td>2001FP185</td><td></td><td>55</td><td>Bowl</td><td>-0.00067</td><td>-0.00005</td><td>-0.00505</td><td>0.00402</td><td>-3.08</td><td>2.69</td><td>0.41</td><td>0.644</td></tr><tr><td>82155</td><td>2001FZ173</td><td></td><td>47</td><td>Double dip</td><td>0.00087</td><td>0.00529</td><td>0.01150</td><td>-0.00107</td><td>-3.62</td><td>-2.51</td><td>0.02</td><td>0.593</td></tr><tr><td>32532</td><td>2001PT13</td><td>Thereus</td><td>8</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>523591</td><td>2001QD298</td><td></td><td>59</td><td>Cliff</td><td>0.00141</td><td>0.00074</td><td>0.02176</td><td>-0.00192</td><td>2.62</td><td>0.83</td><td>1.03</td><td>0.607</td></tr><tr><td>275809</td><td>2001QY297</td><td></td><td>49</td><td>t-Cliff</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>42355</td><td>2002CR46</td><td>Typhon</td><td>41</td><td>Bowl</td><td>-0.00039</td><td>-0.00077</td><td>-0.00419</td><td>0.00849</td><td>-4.75</td><td>3.17</td><td>-0.97</td><td>0.668</td></tr><tr><td>250112</td><td>2002KY14</td><td></td><td>38</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>84522</td><td>2002TC302</td><td></td><td>13</td><td>Cliff</td><td>0.00363</td><td>0.00189</td><td>0.03288</td><td>-0.00027</td><td>4.97</td><td>0.89</td><td>-0.89</td><td>0.670</td></tr><tr><td>55637</td><td>2002UX25</td><td></td><td>7</td><td>Double dip</td><td>-0.00029</td><td>0.00281</td><td>0.01066</td><td>0.00000</td><td>-1.83</td><td>-1.98</td><td>0.22</td><td>0.663</td></tr><tr><td>612533</td><td>2002XV93</td><td></td><td>22</td><td>Bowl</td><td>-0.00111</td><td>0.00022</td><td>0.00246</td><td>0.01096</td><td>-3.53</td><td>1.88</td><td>1.94</td><td>0.628</td></tr><tr><td>120132</td><td>2003FY128</td><td></td><td>116</td><td>Double dip</td><td>0.00032</td><td>0.00274</td><td>0.01171</td><td>0.00059</td><td>-1.11</td><td>-1.88</td><td>0.59</td><td>0.671</td></tr><tr><td>385437</td><td>2003GH55</td><td></td><td>58</td><td>Cliff</td><td>0.00075</td><td>0.00035</td><td>0.01260</td><td>0.00033</td><td>4.04</td><td>0.76</td><td>0.40</td><td>0.662</td></tr><tr><td>174567</td><td>2003MW12</td><td>Varda</td><td>10</td><td>Double dip</td><td>0.00008</td><td>0.00548</td><td>0.01021</td><td>-0.00072</td><td>-3.86</td><td>-3.21</td><td>-1.48</td><td>0.607</td></tr><tr><td>120181</td><td>2003UR292</td><td></td><td>35</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>523601</td><td>2003UY413</td><td></td><td>153</td><td>Double dip</td><td>-0.00025</td><td>0.00478</td><td>0.01306</td><td>-0.00021</td><td>-1.80</td><td>-2.85</td><td>-0.73</td><td>0.667</td></tr><tr><td>416400</td><td>2003UZ117</td><td></td><td>26</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>455502</td><td>2003UZ413</td><td></td><td>27</td><td>Bowl</td><td>-0.00081</td><td>0.00005</td><td>0.00181</td><td>0.00891</td><td>-3.42</td><td>2.10</td><td>1.15</td><td>0.644</td></tr><tr><td>136204</td><td>2003WL7</td><td></td><td>37</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>120216</td><td>2004EW95</td><td></td><td>18</td><td>Bowl</td><td>-0.00007</td><td>-0.00028</td><td>0.00021</td><td>0.00558</td><td>-5.61</td><td>1.69</td><td>-1.53</td><td>0.637</td></tr><tr><td>444030</td><td>2004NT33</td><td></td><td>24</td><td>Bowl</td><td>-0.00156</td><td>0.00001</td><td>-0.00163</td><td>0.01203</td><td>-3.41</td><td>2.40</td><td>2.29</td><td>0.627</td></tr><tr><td>175113</td><td>2004PF115</td><td></td><td>19</td><td>Cliff</td><td>0.00737</td><td>0.00099</td><td>0.02896</td><td>0.00028</td><td>6.27</td><td>1.78</td><td>-1.36</td><td>0.667</td></tr><tr><td>307982</td><td>2004PG115</td><td></td><td>20</td><td>Cliff</td><td>0.00312</td><td>0.00612</td><td>0.01817</td><td>-0.00032</td><td>4.25</td><td>0.74</td><td>-1.67</td><td>0.646</td></tr><tr><td>120348</td><td>2004TY364</td><td></td><td>12</td><td>Double dip</td><td>-0.00024</td><td>0.00408</td><td>0.01616</td><td>-0.00050</td><td>-2.22</td><td>-2.10</td><td>-0.78</td><td>0.653</td></tr><tr><td>144897</td><td>2004UX10</td><td></td><td>114</td><td>Double dip</td><td>0.00014</td><td>0.00342</td><td>0.01477</td><td>0.00164</td><td>-1.21</td><td>-2.72</td><td>0.22</td><td>0.680</td></tr><tr><td>230965</td><td>2004XA192</td><td></td><td>9</td><td>Double dip</td><td>-0.00135</td><td>0.00445</td><td>0.00941</td><td>-0.00048</td><td>-2.35</td><td>-2.50</td><td>-0.73</td><td>0.659</td></tr><tr><td>545293</td><td>2005CC79</td><td></td><td>48</td><td>Bowl</td><td>-0.00036</td><td>-0.00017</td><td>-0.00414</td><td>0.00609</td><td>-3.88</td><td>3.15</td><td>-0.36</td><td>0.668</td></tr><tr><td>469705</td><td>2005EF298</td><td>Kagara</td><td>57</td><td>Cliff</td><td>-0.00026</td><td>0.00072</td><td>0.00513</td><td>0.00051</td><td>4.64</td><td>0.84</td><td>1.12</td><td>0.663</td></tr><tr><td>469750</td><td>2005PU21</td><td></td><td>40</td><td>Cliff</td><td>0.00126</td><td>0.00064</td><td>0.00865</td><td>0.00163</td><td>3.60</td><td>-0.47</td><td>2.10</td><td>0.612</td></tr></tbody></table>
<table><caption>Table 1 (continued) | Spectral group, absorption band areas (in µm) and spectral clustering (PCA and k-means) parameters for DiSCo-TNOs</caption><thead><tr><th>Number</th><th>Provisional designation</th><th>Name</th><th>Observation ID</th><th>Group</th><th>CH<sub>3</sub>OH</th><th>CO<sub>2</sub></th><th>Aliphatic CH</th><th>H<sub>2</sub>O Fresnel</th><th>PC1</th><th>PC2</th><th>PC3</th><th>Silhouette coefficients</th></tr></thead><tbody><tr><td>303775</td><td>2005QU182</td><td></td><td>133</td><td>Double dip</td><td>0.00040</td><td>0.00512</td><td>0.01584</td><td>0.00069</td><td>-0.65</td><td>-1.81</td><td>-0.39</td><td>0.669</td></tr><tr><td>145452</td><td>2005RN43</td><td></td><td>11</td><td>Double dip</td><td>0.00036</td><td>0.00404</td><td>0.01643</td><td>0.00003</td><td>-1.95</td><td>-2.48</td><td>-0.34</td><td>0.670</td></tr><tr><td>145480</td><td>2005TB190</td><td></td><td>25</td><td>Double dip</td><td>-0.00081</td><td>0.00532</td><td>0.01610</td><td>-0.00018</td><td>0.16</td><td>-1.83</td><td>-0.17</td><td>0.656</td></tr><tr><td>444745</td><td>2007JF43</td><td></td><td>29</td><td>Cliff</td><td>0.00475</td><td>0.00207</td><td>0.02994</td><td>-0.00010</td><td>5.55</td><td>1.22</td><td>-0.87</td><td>0.673</td></tr><tr><td>470316</td><td>2007OC10</td><td></td><td>23</td><td>t-Double dip</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>309239</td><td>2007RW10</td><td></td><td>50</td><td>Bowl</td><td>-0.00098</td><td>-0.00009</td><td>0.00063</td><td>0.00562</td><td>-5.10</td><td>2.04</td><td>-1.80</td><td>0.642</td></tr><tr><td>341520</td><td>2007TY430</td><td>Mors</td><td>45-M</td><td>Cliff</td><td>0.00076</td><td>0.00012</td><td>0.01902</td><td>0.00149</td><td>3.06</td><td>-0.47</td><td>1.17</td><td>0.589</td></tr><tr><td>341520</td><td>2007TY430</td><td>Somnus</td><td>45-S</td><td>Cliff</td><td></td><td></td><td></td><td></td><td>4.23</td><td>0.32</td><td>1.34</td><td>0.640</td></tr><tr><td>229762</td><td>2007UK126</td><td>G!kún|' hòmdimà</td><td>2</td><td>Double dip</td><td>-0.00042</td><td>0.00501</td><td>0.01257</td><td>-0.00059</td><td>-1.01</td><td>-2.38</td><td>0.09</td><td>0.678</td></tr><tr><td>470596</td><td>2008NW4</td><td></td><td>36</td><td>Double dip</td><td>0.00179</td><td>0.00319</td><td>0.01694</td><td>-0.00017</td><td>1.42</td><td>-1.32</td><td>0.34</td><td>0.579</td></tr><tr><td>471143</td><td>2010EK139</td><td>Dziewanna</td><td>5</td><td>Double dip</td><td>0.00021</td><td>0.00465</td><td>0.01064</td><td>0.00008</td><td>-0.63</td><td>-2.03</td><td>-0.15</td><td>0.682</td></tr><tr><td>552555</td><td>2010ER65</td><td></td><td>46</td><td>Double dip</td><td>0.00077</td><td>0.00586</td><td>0.02077</td><td>0.00024</td><td>1.81</td><td>-0.76</td><td>-0.83</td><td>0.520</td></tr><tr><td>471137</td><td>2010ET65</td><td></td><td>44</td><td>Double dip</td><td>0.00113</td><td>0.00495</td><td>0.01532</td><td>-0.00001</td><td>0.80</td><td>-1.81</td><td>0.45</td><td>0.628</td></tr><tr><td>310071</td><td>2010KR59</td><td></td><td>17</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>471210</td><td>2010VW11</td><td></td><td>31</td><td>Double dip</td><td>-0.00001</td><td>0.00383</td><td>0.01463</td><td>0.00078</td><td>-0.74</td><td>-2.52</td><td>0.37</td><td>0.680</td></tr><tr><td>445473</td><td>2010VZ98</td><td></td><td>15</td><td>Cliff</td><td>0.00314</td><td>0.00264</td><td>0.01935</td><td>-0.00009</td><td>6.04</td><td>2.12</td><td>-1.78</td><td>0.662</td></tr><tr><td>-</td><td>2012DR30</td><td></td><td>54</td><td>Bowl</td><td>-0.00068</td><td>-0.00023</td><td>-0.00640</td><td>0.00709</td><td>-3.59</td><td>3.16</td><td>-0.57</td><td>0.665</td></tr><tr><td>468861</td><td>2013LU28</td><td></td><td>1</td><td>Bowl</td><td>-0.00033</td><td>-0.00001</td><td>-0.00213</td><td>0.00244</td><td>-4.53</td><td>2.17</td><td>-0.83</td><td>0.657</td></tr><tr><td>523722</td><td>2014LV28</td><td></td><td>42</td><td>Double dip</td><td>0.00034</td><td>0.00374</td><td>0.01656</td><td>-0.00046</td><td>1.79</td><td>0.03</td><td>-0.47</td><td>0.515</td></tr><tr><td>523777</td><td>2014YF50</td><td></td><td>30</td><td>Double dip</td><td>0.00124</td><td>0.00475</td><td>0.01644</td><td>0.00144</td><td>1.51</td><td>-1.57</td><td>0.40</td><td>0.580</td></tr><tr><td>508338</td><td>2015SO20</td><td></td><td>52</td><td>Bowl</td><td>0.00077</td><td>0.00053</td><td>-0.00219</td><td>0.00312</td><td>-3.36</td><td>2.42</td><td>0.01</td><td>0.647</td></tr></tbody></table>

Cluster assignation for 2001 QY<sub>297</sub> and 2007 OC<sub>1</sub> are tentative (see section 'Clustering'). This is indicated in the table as t-cliff and t-double dip. For the spectral classification of the Centaurs, see ref. 20.

below 2.5 µm (Fig. 3). Alternative or additional reddening agents that can produce moderate red slopes from the visible to 2.5 µm are silicates and iron sulfides, such as those commonly found in primitive Solar System dust<sup>25,26</sup>. A weak band at 4.93 µm could be tentatively attributed to an overtone of olivine [(Fe,Mg)<sub>2</sub>SiO<sub>4</sub>]. The presence of refractory materials is also consistent with the low geometric albedo of the bowl group in the visible (ranging from 0.04 to 0.13; Fig. 1b and Extended Data Table 2), which requires substantial volumetric fraction of dark refractory compounds in addition to pure ices.

The double-dip spectral group (43% of the sample) was characterized by a deep absorption at 3.0 µm and a shallower band from 3.3 to 3.7 µm (Fig. 3). The reflectance rises from 3.0 to 3.7 µm to roughly 70% of the value of the continuum at 2.62 µm. At the longest wavelengths, the spectra were dominated by CO<sub>2</sub>, its isotopologue <sup>13</sup>CO<sub>2</sub> and CO. The fundamental absorption of CO<sub>2</sub> at 4.27 µm is bounded by two peaks that rise notably above the surrounding continuum and a deep absorption at 4.06 µm; these distinctive features along the TNO population were further explored in a previous study<sup>27</sup>. The presence of CO<sub>2</sub> in this group was higher than that in bowls and cliffs, as evidenced by the presence of its combination bands at 2.70 µm and, in some cases, at 2.77 µm (Extended Data Fig. 6d). <sup>13</sup>CO<sub>2</sub> was revealed by a sharp band at 4.38 µm

(Extended Data Fig. 6f). We detected the fundamental absorption of CO at 4.68 µm and C-H stretching absorptions of aliphatic complex organics<sup>23</sup> from 3.33 to 3.6 µm. We also report broad absorptions at around 1.5, 2.0, 2.3 and 2.5 µm that we attribute to the O-H, C-H and N-H bands in complex materials. Although the 1.5- and 2.0-µm bands could have a contribution from water ice, their shapes differ from those observed in bowl types (Extended Data Fig. 6a), which, together with the absence of a Fresnel peak at 3.1 µm, further indicates that the surfaces of double-dip TNOs are poorer in water than the bowls. We cannot rule out a possible minor presence of methanol on these surfaces, contributing at 2.27, 2.34 and 3.53 µm. The large absorption at 3 µm could indeed be due to O-H in both organics and methanol, with a possible minor contribution from amorphous water (Extended Data Fig. 6d).

The cliff TNOs (32% of the sample) are objects that revealed many absorption bands (Fig. 3). All of the cliff spectra show a sharp drop in reflectance starting at 2.7 µm, a flat profile from 2.9 to 3.15 µm and then a rise to a local maximum between 3.7 and 3.8 µm at a level of roughly 53% of the 2.62-µm reflectance continuum. The different shapes of the large 3.0-µm band in cliff and double dip suggest the presence of additional O-H and N-H absorptions in cliff TNOs (Extended Data Fig. 6d). At short wavelengths, the spectra are dominated by bands
<figure><img src="image_7.png" /><figcaption>**Fig. 4 | Distribution of molecules between compositional groups.** Band areas (in µm) for the main spectral detections in the trans-Neptunian belt. Colours and symbols represent the different compositional groups. Each panel represents the comparison of the abundance of two different molecules. **a, c, e**, The H₂O (**a**), CH₃OH (**c**) and aliphatic -CH (**e**) versus the CO₂ band areas are clear</figcaption></figure>

discriminators of the bowl, double-dip and cliff groups. The colours and shapes of the symbols are the same as in Fig. 1. The two 'CO₂-transition objects', Huya and 2004 PG115, are clearly visible in **a, c and e** (see Methods for more details). The band areas are presented as the mean of three values calculated using different spectral baselines, and the error bars represent the standard errors of the mean.

corresponding to O-H-, C-H- and N-H-bearing materials, deeper than the analogous features in the double-dip spectra. The 2.3-µm region shows two minima at 2.27 and 2.34 µm, attributed to methanol ice (Extended Data Fig. 6c); a distinctive shoulder confirms this identification within the aliphatic organic band at 3.53 µm (Extended Data Fig. 6d). Some cliff types also showed a weak band at 3.9 µm. This band is seen in CH₃OH, which would be the simplest explanation given the detection of this molecule at other wavelengths, although

we cannot discard the contribution from H₂S (Extended Data Fig. 6e). The fundamental CO₂ absorption is evident but not as dominant as that in the double-dip group, lacking the two peculiar peaks seen for the double-dip group, and the CO₂ combination band at 2.7 µm is shallower (Extended Data Fig. 6d). The fundamental band of CO is less sharp in the cliff type than in the double-dip type (Extended Data Fig. 6f). The cliff spectra show contributions of additional absorptions in the 4.5-4.62 µm range that we attribute C≡N bonds, possibly in complex
organics (for example, tholins) and in OCN⁻ (Extended Data Fig. 6f). Some cliff and double-dip objects have bands at 4.90–4.93 µm that could be due to OCS, CO₂ and/or olivine. The cliff-type spectra have, by far, the reddest spectral slopes in the visible and shortest-wavelength end of the NIR (S' and SIR, in Fig. 1a and Extended Data Table 2), which suggests a high abundance of red, complex tholin-like organics, possibly formed by the irradiation of different ices containing C–H, N–H and O–H.

## Compositional diversity

Here we focus on the overall spectral trends observed for H₂O, CO₂, aliphatic C–H, CH₃OH and organics. We calculated their band areas (see ‘Band areas and parameters’ in Methods, Table 1 and Extended Data Fig. 7) and report them in Fig. 4 to visualize the three groups in terms of their relative molecular abundances. The case of CO has been discussed elsewhere²⁷. To spread the band areas along one axis representing the spectral diversity of our targets, we calculated the Euclidean spectral distance (Methods) of each TNO with respect to the average spectrum of our cold classical TNOs. The results are shown in Fig. 5.

The targets were easily separable into three compositional groups. The band areas of H₂O versus CO₂ were particularly effective in distinguishing the three groups from each other and were even more evident when considering also aliphatic C–H versus CO₂. Water ice bands were clearly observed in the bowl type, but their spectral contribution is much weaker (or even absent) in the double-dip and cliff types. Carbon dioxide bands are very strong in the double-dip type (with the exception of Huya), weaker in the cliff type (with the exception of 2004 PG115) and even weaker in the bowl type. The aliphatic CH features are largely absent in the bowl type, appear in the double-dip type and become stronger in the cliff type. The 2.3- and 2.5-µm bands of CH₃OH and complex organics were observed in the cliff and double-dip objects and absent in the bowl types. They are more intense in a few cliff spectra, which show a clear profile of the methanol bands at 2.27 and 2.34 µm.

In summary, bowl-type surfaces have stronger water bands and weaker C–H bands than cliffs and double dips, with double dips showing stronger CO₂ bands and cliffs having stronger organic and hydrocarbon bands.

## Discussion

Snow lines in the primordial disk, representing condensation of gases onto grains before planetesimal formation²⁸, and/or ice retention lines⁵,¹², that is, locations at which ices are stable against sublimation from the surfaces of newly formed planetesimals are natural explanations for the compositional differences presented above. In fact, PCA indicated that there was no continuum between the bowl group and the cliff and double-dip groups. A very sharp process must be invoked to produce such an abrupt discontinuity. The spectral differences between the cliff and double-dip TNOs are less sharp in the PCA analysis but pronounced when inspecting the spectra, especially in the dominance of the CO₂ and CO absorption bands in the double-dip TNOs. In particular, CO₂ and CH₃OH ice lines are expected to play a major role because these ices are abundant in the interstellar medium (ISM) (for example, ref. 14). CO₂ was observed at the surface of all objects²⁷, but the band areas dramatically increased from bowl to double-dip TNOs and then decreased from double-dip to cliff TNOs. Methanol was detected in some cliffs. The lack of clear detection of water ice in the methanol-rich objects is compatible with the heretofore so called ‘anomalous’ high abundance of methanol ice relative to water ice on cold classical Arrokhof²⁹.

To gain more insight into which ice lines produced the observed compositional groups, we examined the association between compositional groups and dynamical classes (Fig. 1 and Extended Data Table 2). All five cold classical TNOs in our sample are in the cliff spectral group, six if we include 2001 QY₂⁹₇, which has tentatively been included in the cliff group via visual inspection according to its negative SIR₃. According to current models of planetary migration⁶,³⁰⁻³², the cold classicals formed furthest out in the disk. Generally, both the bowl and double-dip

<figure><img src="image_8.png" /></figure>

**Fig. 5 | Ice line hypothesis in relation to the molecules dominating each compositional group.** The H₂O, CH₃OH and CO₂ band areas (in µm) of the individual spectra of the bowl, double-dip and cliff types are represented in grey. The coloured symbols correspond to the average values for each group ± standard deviation as a function of the Pearson coefficient spectral distance to the average spectrum of our cold classical TNOs, which are the objects believed to be formed in the outer part of the disk. The existence of three main compositional groups and the observed trends in the band areas can be explained by crossing different ice retention lines in the early Solar System. Symbol colours and shapes are as in Fig. 1. The band areas are presented as the mean of the three values calculated using different spectral baselines. The error bars of the mean values of the three spectral groups are the standard deviations.

objects are on more excited orbits (higher inclination and eccentricity) than the cliff objects are. Additionally, the two bowl-type objects in our sample were originally coming from the Oort cloud: 2012DR₃₀ and 2013LU₂₈ (refs. 33,34). Most dynamical models suggest that Oort cloud objects formed closer to the giant planets³⁵ and were violently ejected by them. This suggests that objects were formed in the order bowl, double dip and cliff, with increasing distance from the Sun (see Fig. 5). Interestingly, the eight DiSCo detached objects (Extended Data Table 2) were all double dips. According to our scenario, the abundance of double dips suggests that most detached objects formed in the intermediate part of the disk. No current evidence indicates that this excited dynamical class has a distinct origin within the PPD, presenting a new and interesting constraint for dynamical models of Solar System formation.

Models of volatile evaporation from the early surfaces, after the planetesimals are formed, predict retention lines of H₂O, CO₂, CH₃OH, C₂H₂, C₂H₆, HCN and NH₃ in order of increasing planetesimal formation distance from the Sun¹². This trend agrees very well with the sequence of bowl < double dip < cliff in an order of formation distance, as shown in Fig. 5. In this scenario, bowl types are essentially formed between the H₂O and CO₂ retention lines, whereas double-dip TNOs require a much more efficient retention of CO₂. The cliff TNOs are certainly formed beyond the CH₃OH retention line, and some of them probably also
beyond the C₂H₆ and HCN retention lines (possibly even beyond the NH₃ line in some cases), which can increase the local C/O ratio and explain the presence of N-bearing species at their surface. In other words, although the sharp difference between the bowl and double dip can be explained by a sudden crossing of the CO₂ line, the less sharp transition between double dip and cliff (Figs. 2, 4 and 5 and Supplementary Fig. 1) could be the result of crossing several molecular lines (CH₃OH, C₂H₆, HCN and so on) in the original PPD, rather than a result of late evolution.

Irradiation by energetic ions and photons from the Sun plays an additional role in the evolution of the surfaces. In the DiSCo dataset, CH₃OH is less frequently observed than either H₂O or CO₂, presumably because it can be easily destroyed by surface irradiation³⁶, unlike H₂O and CO₂, which can actually reform in an irradiation environment³⁷,³⁸. In the cliff type, methanol NIR combination modes at 2.27 and 2.34 µm were more easily observed than its fundamental CH₃ vibration at 3.53 µm. Because the combination modes have weaker band strengths than the fundamental mode, they can probe deeper layers. The weak detection of the 3.53-µm band thus suggests stratification: methanol is destroyed by irradiation at the surface³⁹, but it is preserved in the subsurface. In turn, irradiated CH₃OH provides building blocks for redder and more complex organics at the surface³⁹,⁴⁰ and some additional CO₂ (ref. 24).

Methane and ammonia are also abundant in disks¹⁴, but we did not detect them in the DiSCo sample because they were not easily retained on medium-sized TNOs³. In addition, they can be destroyed by irradiation³⁶,⁴¹ supplying C, N and H for more complex molecules to form, such as those detected in cliff TNOs. Other ices (C₂H₆, HCN and so on), when irradiated, may provide additional atoms for red complex organics. Interestingly, if the presence of sulfur-bearing species in the cliff TNOs is confirmed in the future, it would make this group the one closer to the composition of PPDs¹⁴ and comets⁴². Under irradiation, S-rich molecules can provide additional colouration¹³. In contrast, complex organic chemistry driven by energetic processes such as ion irradiation is not favoured on bowl surfaces because of their low C/O ratio. Previous studies have invoked ice lines as the origin of the visible and NIR colour diversity of TNOs¹¹,⁴⁴. Our results finally unlocked the interpretation of colour bimodality, providing compositional information.

The young Sun was a much more active star than today, producing higher ion and photon fluxes (for example, refs. 45,46). Thus, the complex organics observed on many TNOs may be the result of this early irradiation of C- and N-rich surfaces. However, if escape timescales on the early planetesimals were shorter than irradiation timescales, then the retention lines were the main driver in sculpting the early surfaces¹²; hence, subsequent irradiation would only produce additional surface evolution within the three groups. In this respect, other molecular differences between or within groups can be attributed to a combination of specific retention lines with heterogeneities in the disk or post-accretion and post-migration processes (long-term irradiation and collisions) and shall be investigated in more detail in future studies.

Through DiSCo, JWST gives us a new view of the diversity of medium-sized TNOs, with the discovery of three distinct compositional groups. Overall, the C/O and (CH + NH)/(C + O) ratios at the surface of TNOs in their early times, before planetary migrations, emerged as major actors in establishing the surface compositional differences among the TNO groups that we observed today. We propose that spectral groups are fossil remnants of groups of medium-sized icy planetesimals in the disk. If this is the case, they provide a picture of the retention lines in the Solar System just before a major planetary migration.

In view of the existence of the three main categories of TNOs, we can now observe other minor Solar System bodies in perspective, such as Centaurs, Trojans of the giant planets and comets. Combining the DiCo results with the JWST observations of all these populations will provide a new window for the early epochs of our planetary system.

# Methods

## Data acquisition and reduction

The NIR spectral observations presented in this study were obtained using the JWST NIRSpec as part of Cycle 1 programme 2418 (Principal Investigator: N. Pinilla-Alonso). We used the NIRSpec IFU with the PRISM disperser and CLEAR filter combination, covering 0.6–5.3 µm at resolving power R ≈ 100, to obtain our spectra. The IFU also provides spatial information, allowing us to identify the target within the 3"-square field of view. The dates, total photon-collecting durations and other observation circumstances for all 59 targets are presented in Extended Data Table 2. Some observations were skipped entirely because of guide star acquisition failures at the beginning of the observation (Obs. 4, 24 and 53), whereas others suffered guide star issues in the middle of the observation (Obs. 14 and 16), resulting in less than four dither positions. In the latter case, the truncated observations were combined with the repeat observations (Obs. 114 and 116, respectively), under the assumption that rotational variations would be insignificant. A handful of other observations suffered from micro-shutter assembly (MSA) electrical shorts that produced bright bars across the IFU field of view (Obs. 23, 33 and 49). To correct for these stationary artefacts, the median of the four dithers was taken and subtracted from each individual dither; this resulted in the removal of the MSA short signature but at the cost of added noise in the extracted spectrum. In one case (Obs. 17), the TNO passed too close to a background star over the course of the observation, resulting in notable stellar contamination of the TNO spectrum. This particular spectrum is not presented in this paper.

The general strategy was to observe each target for approximately 1 h using the NRSIRS2RAPID readout pattern spread across four separate dithers. Each dither comprised a single integration to maximize the number of groups and, by extension, the signal-to-noise ratio (SNR). Target acquisition was not specified for any target, given their relatively small positional uncertainties and the size of the IFU field of view (3" × 3"). Instead, we relied on blind pointing with the telescope, which has a pointing precision of 0.1" (1-σ), equivalent to the size of a single NIRSpec IFU pixel. The 4-point dither was selected for minimum throw distances when the target was placed near the edge of the IFU field of view due to, for example, minor pointing anomalies.

Observations of the G3V-type star, referred to as SNAP-2 (ref. 47), and alternatively known as 2MASS J16194609+5534178 and Gaia DR3 1429541695100150656, were obtained as part of the commissioning programme 1128 (Principal Investigator: N. Lutzgendorf) and used to perform solar correction for all TNO data. The NIRSpec/IFU data of this star were obtained with the PRISM/CLEAR combination and the NRSIRS2RAPID readout pattern, with 20 total dither positions.

To ensure the most up-to-date calibration, the 'uncal' data for each observation were downloaded from the Barbara A. Mikulski Archive for Space Telescopes using the 'jwst_mast_query' tool and run locally through the latest version of the JWST data calibration pipeline. All data presented in this paper were processed using pipeline v.1.11.4 and the context file 'jwst_1119.pmap'. The pipeline was run with all default parameters but with an added 'de-striping' step to remove the 1/f pattern noise. First, the Detector1 and Spec2 steps of the pipeline were run, with the 'cal' file output from Spec2 used to construct a mask with all not-a-number (NaN) values set to 1 and all non-NaN values set to NaN. The 'rate' file output by the Detector1 step was then multiplied by the mask to mask out the illuminated portions of the detector. Additionally, the central -200 rows of the 'rate' file were masked out due to leakage through the NIRSpec fixed slits, which are always open. For each pixel in each column, a ±200-pixel moving median was calculated, and the result was subtracted from that pixel in the original, unmasked 'rate' file. The Spec2 step was then re-run on the de-striped 'rate' file to produce a calibrated spectral data cube (an 's3d' file) for each dither. The spectral data cubes were produced in the 'skyalign' reference frame, with north up and east to the left.
The spectral extraction step made use of a 'template PSF-fitting' routine. We first constructed the wavelength array using the CRVAL3 and CDELT3 header keywords and trimmed wavelengths <0.7 and >5.1 µm. The DQ (data quality) extension in the fits files was then used to identify pixels flagged by the pipeline; any pixel with a value >0 was set to NaN for the remainder of the extraction. The rough centroid position of the target PSF was determined by eye, and the remaining outlier pixels (due to artefacts or background objects) more than 5 pixels from the centroid position were set to NaN. Background subtraction was performed on a slice-by-slice basis by calculating the median of all >5 pixels from the centroid position and subtracting that value from all pixels in the slice. Stepping through the spectral data cube one slice at a time, a template PSF was calculated as the median of the ten background-subtracted slices ahead of and behind the slice under consideration (inclusive, for a total of 21 slices included in the median). The template PSF was trimmed to a 9 × 9 postage stamp centred on the centroid position, with all pixels outside this region set to NaN; the purpose here was to eliminate the leverage of more distant pixels in the fit. The trimmed template PSF was then normalized to unity within the vignette. The template PSF was fitted to the slice under consideration, using the ratio of template PSF to data and the median background computed from the region >5 pixels from the PSF centroid as initial guesses for the fitting routine. The 'scipy.optimize.minimize' function was used with the Nelder-Mead (amoeba) method to determine the best-fit values for the flux scaling factor and background. This process was performed iteratively with additional masking of bad pixels after each of the three iterations. The model (the template PSF multiplied by the flux scaling factor plus the background) was subtracted from the data, and any pixel with a value >5-σ from the mean was treated as an outlier and set to NaN. The final PSF model was calculated by multiplying each slice of the template PSF by the flux scaling factor and subtracting the residual background. Finally, the flux was extracted from the template PSF model within a 3.5-pixel-radius circular aperture centred on the PSF centroid. The same extraction method was used for the TNOs in programme 2418 and for the standard star in programme 1128.

Spectra extracted from individual dithers were then combined, and solar-flux correction was performed. All dithers for the standard star were resampled onto the same wavelength grid, and the median was computed within each wavelength bin. Three iterations of outlier rejection were then performed: a 21-point moving median and standard deviation were calculated, and any points >3-σ were replaced with the median value. For the TNO spectra, all dithers were resampled onto the same wavelength grid as the standard star, and a median was performed, followed by the division of the median by the standard star. Outlier rejection was then performed on the corrected TNO spectrum. Uncertainties in each median spectrum were computed as the median absolute deviation over the four dithers within each wavelength bin, and uncertainties were propagated for the solar-corrected TNO spectrum taking into account the uncertainties in the standard star median spectrum.

Of the observed 59 objects, 2005 QU<sub>182</sub>, 2007 OC<sub>10</sub> and 2001 QY<sub>297</sub>, which were impacted by an electrical short of the NIRSpec MSA, have low SNRs, especially at the longest wavelengths where the flux of the targets is lower. We cut the noisy part of the flux in the representation. The flux of 2010 KR<sub>50</sub> also has a higher uncertainty than the rest of the sample due to a nearby bright background star. Other noisy fluxes, especially longer than 3.5 µm, correspond to the faintest targets in our sample, Kågåra, 2003 GH<sub>55</sub>, Borasisi and 2001 QD<sub>298</sub>, all of which have a relative magnitude in the visible above 22, at the limit of NIRSpec detection at the longest wavelengths.

## Description of the sample

The DiSCo sample contained 59 total targets spanning the full range of trans-Neptunian dynamical classes, including five Centaurs, with visible geometric albedos from 0.04 to 0.33 and estimated diameters from

35 to 792 km (Extended Data Table 2 and Supplementary Fig. 2). Twelve targets correspond to binary or multiple systems, with Mors–Somnus being the first binary TNO resolved using spectroscopic observations<sup>48</sup>; hence, we show their spectra independently. All the DiSCo objects have V magnitudes brighter than 22.36, and they have well-determined orbits with ephemeris uncertainties ≤2". Additionally, we retained in our sample only those TNOs that were out of the galactic plane by >15° to avoid contamination by field stars. To optimize the value of our library of spectra, we planned to overlap with the key programme of the Herschel Space Observatory, 'TNOs Are Cool'<sup>49</sup>. The survey resulted in diameters and geometric albedos in the visible for about 170 TNOs and Centaurs. For those DiSCo objects not included in the 'TNOs Are Cool' survey, we used the average albedo corresponding to their dynamical class in a previous study<sup>49</sup> and their $H_v$ from JPL Horizons (https://ssd.jpl.nasa.gov/) to estimate the diameter and its 1-σ error.

We provide the dynamical classification for each target in Extended Data Table 2, established using a supervised machine learning classifier<sup>50</sup>. This classifier uses the SSBN07 dynamical scheme<sup>51</sup>, defining five classes: classical, scattering, resonant, detached objects and Centaurs. Cold classical TNOs are defined as the lowest-i and low-e TNOs in the classical belt, whereas hot classical TNOs are the dynamically excited classical objects. Two objects in our sample have uncertain origins, potentially from the Oort cloud<sup>33</sup>. One is 2012 DR30 (ref. 34), which belongs to a small group of poorly understood TNOs (HiHq) characterized by high inclinations ($i > 60°$) and high perihelia ($q \ge 15$ au). The other object, 2013 LU28, moves in a near-polar orbit and is a candidate transient co-orbital to Uranus<sup>52</sup>, although it has also been classified as a retrograde Centaur and, in a previous study<sup>50</sup>, as scattering. Borasisi ($a = 44.1200$ au, $e = 0.0890$ and $i = 0.6000°$) is classified as a cold classical after private communication with K. Volk. Although Borasisi was classified as a resonant object in a previous study<sup>50</sup>, this classification is uncertain, and it could still be a cold classical slowly diffusing into a 7:4 resonance.

Our sample also covers the full range of sizes and geometric albedo diversity found in the trans-Neptunian population except for the dwarf planets Pluto, Eris, Makemake and Haumea, and a handful of large TNO dwarf planet candidates such as Sedna, Quaoar, Gonggong and Orcus. All of the aforementioned objects are targets of Guaranteed Time Observations programmes 1191, 1231, 1254, 1272 and 1273 of the first cycle of JWST; hence, all programmes are complementary. One small group not fully covered by DiSCo is the Haumea family; these objects have peculiar visible and NIR spectra as a result of surfaces dominated by water ice<sup>43–57</sup>. Four members of this high-albedo family are included in the aforementioned Guaranteed Time Observations programmes, with a fifth member, 2003 UZ<sub>117</sub>, included in the DiSCo sample. Within the DiSCo sample, the faintest TNOs were under-sampled due to the inability to obtain meaningful fluxes beyond 3.5 µm for V magnitude ≥ 22.5. This excludes objects smaller than about 170 km in diameter, except for the Centaur objects, which are closer. This will likely result in bias when trying to establish correlations between size and surface composition. In terms of visible colours, DiSCo covers from neutral objects, such as 2004 NT<sub>33</sub> ($S' = 2.54 \pm 0.9\%/0.1$ µm), to ultra-red objects, such as 2007 JF<sub>43</sub> ($S' = 40.89 \pm 0.9\%/0.1$ µm; Fig. 1 and Extended Data Table 2). The Haumea family member 2003 UZ<sub>117</sub> is the only DiSCo object with a negative slope in the visible wavelength region.

When studying the colour in the IR below 2.7 µm, where the continuum can be easily fit by a straight line, we observed a clear change in the slope for all the targets in the double-dip and cliff types at 1.2 µm. To compare the three groups of TNOs, we defined $SIR_1$ and $SIR_2$ as the slope of the continuum between 0.7 and 1.2, and between 1.15 and 2.42, respectively, normalized at 1.175 µm (where both intervals overlap). We used the expression $S[\lambda_1, \lambda_1/R_{1.175}]$ expressed in (%/0.1 µm), where S is the slope calculated between the extremes of each interval, and $R_{1.175}$ is the reflectance at the normalization wavelength (1.175 µm). From the literature, we collected the slope in the visible (see Extended Data Table 2 for reference). All three slopes are expressed in units of %/0.1 µm.
## Compositional group distribution in relation with physical parameters

As a result of our study, it is interesting to inspect the distribution of different compositional groups in terms of their physical parameters. The bowl-type TNOs were slightly darker red than neutral objects in the visible, with 80% of them below the average geometric albedo of the sample (11.7% ± 6.1), with all of them below the average visible slope of $S' = 20.7 \pm 9.9\%/0.1 \mu m$. In IR, there was no change in the slope at 1.2 µm, and these objects continued being reddish up to 2.5 µm.

The double-dip and cliff types, however, were red to extremely red in the visible up to 1.2 µm (S' and $SIR_1 = 19.9 \pm 1.9$ and $31.4 \pm 2.4\%/0.1 \mu m$, respectively), but they became neutral to bluish from 1.2 to 2.5 µm with the double-dip type showing the smallest dispersion of colour in the visible and IR (Fig. 1). This change in slope was observed previously through spectroscopy and spectrophotometry, but we can now associate it with the surface composition. The bowl type is dark, neutral to reddish (in the visible and IR wavelengths), with surfaces dominated by water ice and dust. Some dust materials, such as amorphous silicates, do not have clear absorption features in the Webb spectral wavelength range, other than a reddish colour. Amorphous silicate dust, when mixed with H₂O, could be responsible for the slope of the bowl spectra up to 2.3 µm and also their low albedos. Meanwhile, the double dips and cliffs are bright, visible-red and NIR-blue (beyond 1.2 µm) small bodies, possibly as a result of a stronger surface contribution, with respect to bowls, of organics, CH₃OH and CO₂, which could be responsible for the higher visible albedo of these surfaces. The hinted relations between dynamical class and compositional groups (described in the discussion) and the lack of a clear relation with size have to be explored further and shall provide a totally new window in the study of different epochs of our Solar System.

## Clustering

Spectral clustering was performed in Quasar (https://quasar codes) using the Orange toolbox⁵⁸. In preparation for the spectral clustering, after testing different normalization wavelengths (see below), we scaled all spectra to unity at 2.6 µm and considered the spectral range between 0.75 and 5.1 µm. We excluded Centaurs (Extended Data Fig. 4) from the spectral clustering because they may be affected by processes such as ice sublimation and activity²⁰. We also excluded 2003 UZ 117, the spectrum of which indicates that it belongs to the Haumea family. It is also a spectral outlier, as determined by the different clustering methods (see below).

To remove some noisy spectra from the dataset before applying the final clustering, we first divided each spectrum by its corresponding smoothed spectrum using a Savitzky-Golay filter with a window of 11 points and a second-order polynomial function for the convolution⁵⁹. The ratioed spectra (four examples are given in the top panel of Supplementary Fig. 3) were analysed by hierarchical clustering with a Euclidean distance that separated, in order of decreasing distance, Somnus, 2001 QY297, and 2007 OC10 (Obs. ID 45-S, 49 and 23, respectively) from the rest of the dataset. We then derived an index of spectral quality (proportional to the SNR) for each object by calculating the inverse of the r.m.s. deviation in the spectra ratioed to their smoothed spectra (see the bottom panel of Supplementary Fig. 3). Again, the top noisy spectra were found to be (in order of increasing SNR) Somnus, 2001 QY297 and 2007 OC10. Thus, we excluded these three spectra from the calculation of the band areas (see below), but we retained Somnus for the final clustering, which allowed us to verify that the spectral similarity of the Mors–Somnus binary components⁴⁸ is valid when they are considered in the largest DiSco dataset (they are both cliffs). We attributed a tentative spectral group to these bodies based on a visual comparison of their spectral features with the most distinctive features in the representative spectrum of each cluster. In this way, we have a total of 51 objects for spectral clustering, of different sizes from about 100–800 km, belonging to all dynamical classes of TNOs.

We applied a k-means clustering method to the original reflectance spectra, with a free number of clusters from two to ten, and a k-means++ algorithm for initialization. The average silhouette score⁶⁰ obtained showed a local maximum when using the three clusters (Supplementary Fig. 1a). The k-means centroids of the three clusters are shown in Fig. 3, and they correspond to the median spectra of the three spectral groups found in this study: bowl, double dip and cliff. The range of variation in each group around the centroid is shown in Fig. 3.

We also tried different normalizations at other wavelengths and calculated the corresponding silhouette scores of the k-means clustering. Four examples are shown in Supplementary Fig. 1a. The silhouette score had a local maximum when the spectra were normalized at 2.6 µm. The region of 2.6 µm was relatively free from absorption bands. In addition, being close to the centre of the NIRSpec range, a normalization at 2.6 µm has the advantage of better visualization of the differences in slope below the normalization point and the different band shapes around 3 µm and above.

The discovery of the three main spectral groups was confirmed by an independent hierarchical clustering. We calculated a matrix of spectral distances for the 51 objects. We tested both Euclidean (a straight line distance between two spectra) and cosine (1-similarity, calculated using the cosine of the angle between two vectors of an inner product space) distances⁶¹. We did not use any reference spectrum here; for each TNO spectrum, the distances were calculated with respect to each of the other TNOs. We then performed hierarchical clustering from the obtained matrix of distances using an 'average linkage' to compute the average distance between the elements of different clusters. The corresponding dendrograms for Euclidean and cosine distances are shown in Extended Data Fig. 5. The three main spectral groups identified by k-means were also identified using hierarchical clustering, with double-dip objects found in between bowl and cliff objects. All the individual objects belonged to the same group in both clusterings.

Finally, we performed PCA using three components, obtaining an explained variance of about 92%. The results are reported in Fig. 2 for PC1 and PC2, where bowl types are extremely well separated from double-dip and cliff types. Double dip and cliff show a more continuous distribution. This can also be observed in some of the band areas (Fig. 4) and k-means clustering. In Table 1 and Supplementary Fig. 1b, we report the silhouette coefficients⁶⁰ of each DiSco TNO, showing how close each point in one cluster is to points in the neighbouring k-means clusters for the three groups (bowl, double dip and cliff). Supplementary Fig. 1b shows that the bowls had no objects with relatively low silhouette coefficients, again implying that their cluster was somewhat more separated than the other two. Two double dips (Obs. ID 42 and 46) had relatively lower coefficients, indicating that they were close to the cliff group, as can also be seen in the PCA plot (Fig. 2). However, in the PCA plot (Fig. 2), no cliff was found in the double-dip area, and vice versa, indicating once again that there was a clear separation and no overlap between the two groups. Changing the normalization modifies the PCA values, but the detection of the three clusters remains valid for all normalizations.

Two clear exceptions exist: TNOs Huya (Obs. ID 3) and 2004 PG115 (Obs. ID 20) are classified as double dip and cliff, respectively, by the two different clustering methods (k-means and hierarchical). However, in terms of the CO₂ band profile and area, they behave as cliff and double dip, respectively, as can be seen in Fig. 4a,c,e. These two possible 'CO₂-transition objects' will be interesting cases to study in more detail in future studies for a better understanding of the molecular differences between the spectral groups.

## Spectral attribution

A summary of spectral attribution is given in Extended Data Table 3.

**Water ice.** The 1.5-µm band region is associated with the first overtone of the O–H stretching mode of H₂O ice⁶². The narrow 1.65-µm feature is characteristic of crystalline water ice but is very poorly resolved in
the PRISM spectra because of the low resolving power (R ≈ 30) at that wavelength. The broad 2.0-µm feature is attributed to combination modes⁶³. The most intense feature is the broad 3-µm absorption of the fundamental O-H stretching mode. The 3.1-µm peak in the midst of the 3-µm band is the Fresnel peak, which is also characteristic of crystalline water ice and arises when a transition between volume and surface scattering occurs. This peak was observed on Enceladus⁶⁴ and on Callisto, Europa and Ganymede, where it was used, alongside the 1.65-µm band, to estimate the ratio between amorphous and crystalline ice at different depths⁶⁵. Both the 1.65- and 2.0-µm bands are sensitive to temperature⁶⁶,⁶⁷. Finally, water ice has a very broad 4.5-µm band attributed to a combination of bending and libration modes⁶⁸. Until now, water ice is the only widespread ice detected on the surface of TNOs⁶⁹.

**Carbon dioxide.** Similar to water ice, CO$_{2}$ has multiple features across the wavelength range. The 4.26-µm band is the $v_{3}$ fundamental antisymmetric stretching mode. The 2.70-µm band is the $v_{1} + v_{3}$ combination mode and is observed on both cliffs and double dips, but most intense on the latter, where the weaker $2v_{2} + v_{3}$ was also seen at 2.77 µm (ref. 70). $^{13}$CO$_{2}$ was firmly detected on double dips by its $v_{3}$ mode at 4.38 µm. As shown in Extended Data Fig. 2, the fundamental band of CO$_{2}$ has a very peculiar shape. This is described in detail and modelled in a previous study²⁷.

**Carbon monoxide.** CO is detected on objects where CO$_{2}$ bands are strong²⁷, owing to the 4.68-µm feature, which corresponds to its fundamental C=O stretching mode⁷¹. Although CO is one of the most abundant molecules detected in comets and interstellar ice mantles, it is also among the most volatile. Hence, it was previously thought to be depleted in TNOs⁷². To be preserved on the surface of TNOs, CO must be retained in a less volatile ice/material such as CO$_{2}$.

**Methanol.** CH$_{3}$OH has two combinations involving the asymmetric stretching modes and symmetric stretching modes of the -CH$_{3}$ group at 2.27 and 2.34 µm (ref. 73), respectively. The first, being the most intense and least affected by space weathering⁷⁴, allowed the detection of methanol on the Centaur Pholus⁷³, the plutino 2002 VE$_{6}$ (ref. 75) and the cold classical Arroloth⁷⁹. CH$_{3}$OH shares the 3-µm -OH stretching and 3.3-µm -CH stretching of all alcohols, which makes it difficult to separate it from other -OH-bearing organics. However, the 3.53-µm symmetric stretching of the -CH$_{3}$ group lies at longer wavelengths than most C-H bands and can help detect methanol. Only a weak peak in this region can be identified in the double-dip and cliff spectra, probably because of the high destruction rate of CH$_{3}$OH under irradiation²⁴ at the surface. H$_{2}$CO could also account for a fraction of the 3.53-µm band⁷⁶. Finally, CH$_{3}$OH has a weak band, the $2v_{2}$ overtone at 4.9 µm, but its contribution is expected to be very small, as in the case of the interstellar 4.9-µm absorption⁷⁶.

**Complex organics.** By complex organics, we refer to a broad range of materials, from organic molecules to macromolecular structures (including tholins and refractory residues), in which a variety of functional groups are expected under irradiation of materials with a starting elemental composition of C, H, O and N: alcohols (-OH), amines (-NH$_{2}$, -NHR and -NR$_{2}$), carbonyles (-CO), nitriles (-CN) and others.

The 1.5-µm broad feature in double dip and cliff can be a blend of the first overtone of C-H, N-H and O-H bonds. Absorptions of around 2 µm in these groups can be attributed to a broad range of organic features: C=O second overtone, O-H and C-H combinations, N-H overtone and combinations⁶². Tholins⁷⁷,⁷⁸ show a particularly strong 1.95-µm absorption, which can be attributed to a combination involving C=N⁷⁹. The 2.3- and 2.5-µm bands can be associated with combinations of C-H stretching and bending modes⁸⁰, which are seen in coals⁸¹. Combinations involving N-H in primary and secondary amines can also contribute to the 2.3-µm band⁴¹. In tholins⁷⁷, the 2.3-µm band is assigned to C=N overtone based on a previous study investigating poly-HCN as the source of a 2.25-µm feature on lapetus and comets⁸².

Organics can also contribute to the absorptions at about 2.9-3.3 µm that can be assigned to O-H and possibly N-H stretching modes. The 3.3- to 3.5-µm absorptions are C-H stretching modes found in aliphatic, conjugated and aromatic molecules, common to a broad range of complex organics.

Tholins, anhydrous poly-HCN and refractory residues display a strong band⁸² attributed to a fundamental stretching mode in nitrile or cyanates (-OCN) and isocyanates (-NCO), with a position varying from 4.5 to 4.6 µm. In ISM ices, the carrier of the 4.62-µm band has been extensively discussed⁸³ and attributed to the OCN⁻ molecule, where $NH_{4}^{+}$ acts as the counterion. Here OCN⁻ is also a strong candidate for the 4.6-µm feature, as it is a major product of the irradiation of ices with these three elements. A 4.5-µm feature has recently been observed on Enceladus using JWST⁶⁴ and attributed to nitrile and/or (iso)cyanate compounds, such as those found in refractory residues⁸¹. Previously, a 4.57-µm feature was detected on Callisto and Ganymede and attributed to C=N-bearing organics⁸⁵.

Further indication that this series of bands can be attributed to complex organics is that they are the strongest for the reddest objects in our sample. In summary, NIR features on the double dip and cliff can be considered as markers of organics.

**Sulfur compounds.** A refractory residue containing sulfur⁸⁶ and tholin prepared with H$_{2}$S⁸² displayed an intense 4.9-µm band. The simple molecule OCS also has a strong 4.9-µm band associated with the $v_{3}$ C=O stretching mode⁸⁷. OCS was observed in dense molecular clouds⁸⁸ and detected in comets⁸⁹,⁹⁰, and is thus a plausible candidate to be present on TNO surfaces. We note that CO$_{3}$, formed by the irradiation of CO$_{2}$, also absorbs at 4.9 µm (ref. 91) and could thus be an important contributor to the 4.9 µm in double dips. A weak 3.9-µm feature observed in the cliff-type TNOs could be associated with the S-H stretching modes either in H$_{2}$S or as a thiol function (-SH) in CH$_{3}$SH and more complex molecules⁹². H$_{2}$S was detected in at least ten comets⁸⁹, and CH$_{3}$SH was detected in 67/P⁹³. Although SO$_{2}$ was detected in comet Hale-Bopp⁸⁹, its main features below 5 µm were the weak $v_{1} + v_{3}$ combination mode at 4.07 µm and the first overtone $2v_{1}$ at 4.37 µm (ref. 94), making it difficult to detect because of its proximity to the very strong CO$_{2}$ bands. We did not detect a 1.8-µm absorption that was attributed to sulfur-bearing complex organics at the surface of Arroloth⁹⁵.

**Silicates.** Olivine has combination- overtone bands in the 4.9- to 5.2-µm region⁹⁶, with peak position varying with the Mg/Fe ratio. In particular, the weak band of 4.93 µm observed in bowl TNOs can be tentatively attributed to olivine. Olivine is abundant in cometary dust and in meteorites, and together with pyroxene and amorphous silicates, it is often mixed at sub-wavelength scale with iron sulfides, iron oxides, carbons and other molecular ingredients in primitive dust, which can suppress the silicate features in the visible and near IR⁸¹. The result is often variable reddish slopes extending well into the NIR, consistent with the characteristic slope of bowl-type spectra.

## Band areas and parameters

We calculated band areas for the 2.3- and 2.5-µm bands attributed to methanol and CH- and NH-bearing species (including tholins and complex organics), the 2.7-µm overtone band of CO$_{2}$ and the aliphatic CH stretching bands (including CH$_{2}$ and CH$_{3}$ modes). For these bands, we calculated the areas in a logarithmic space of reflectance because they were observed in a volume scattering regime (in which absorption bands are observed towards the bottom). We also calculated the area of the Fresnel peak of water ice at about 3.1 µm, directly in a reflectance space, because it was observed in a surface scattering regime (the absorption peak was observed towards the top). Examples are reported in Extended Data Fig. 7. The integration limits were 2.22-2.58 µm for CH$_{3}$OH, 2.67-2.72 µm for CO$_{2}$, 3.36-3.56 µm for C-H and 3.05-3.16 µm
for H₂O. We chose these four bands because they sample very different ices and compounds, and they were observed in the regions of the spectra with relatively high SNR. The main goal was to illustrate the relative variations among the groups. Absolute quantification will require dedicated spectral modelling in future studies.

Band areas may strongly depend on the choice of the local continuum. Therefore, we calculated three baselines (a linear function and second-order and third-order polynomial functions) for each spectrum, and we averaged the areas obtained using the three methods. Generally, the second-order polynomial provides a good description of the continuum, but there are cases where the linear baseline or third-order polynomial functions work better. Averaging the three values and taking the standard error make the calculation of the band area less dependent on systematic errors. For some objects, the baselines can produce slightly negative areas for some bands, particularly in those objects where the band is not present and the continuum is very curved (for instance, the band area for aliphatic C–H in bowls, where the band is absent). In any case, we verified that the main result that the detected molecules are good discriminators of the three main spectral groups is still valid even when using a single baseline function.

The error bars for the band areas are given in Fig. 4. The error in the band areas coming from the choice of the continuum is generally higher than the Gaussian error associated with the median absolute deviation over the four dithers. Thus, we used the standard error from the three baseline calculations (see above).

## Data availability

The JWST data used in this analysis are publicly available from the STScl MAST Archive (https://doi.org/10.17909/r2zp-r280).

## References

1. Gil-Hutton, R. Color diversity among Kuiper belt objects: the collisional resurfacing model revisited. *Planet. Space Sci.* **50**, 57–62 (2002).

2. Métayer, R. et al. JWST/NIRSpec prospects on transneptunian objects. *Front. Astron. Space Sci.* **6** https://doi.org/10.3389/fspas.2019.00008 (2019).

3. Schaller, E. L. & Brown, M. E. Volatile loss and retention on Kuiper Belt objects. *Astrophys. J. Lett.* **659**, L61–L64 (2007).

4. Levi, A. & Podolak, M. Corona-like atmospheric escape from KBOs. II. The behavior of aerosols. *Icarus* **203**, 610–625 (2009).

5. Young, L. A., Braga-Ribas, F. & Johnson, R. E. in *The Trans-Neptunian Solar System* (eds Prialnik, D. et al.) 127–151 (Elsevier, 2020).

6. Nesvorný, D. et al. OSSOS XX: the meaning of Kuiper Belt colors. *Astron. J.* **160**, 46 (2020).

7. Luu, J. & Jewitt, D. Color diversity among the Centaurs and Kuiper Belt objects. *Astron. J.* **112**, 2310–2318 (1996).

8. Tegler, S. C. & Romanishin, W. Two distinct populations of Kuiper-Belt objects. *Nature* **392**, 49–51 (1998).

9. Lacerda, P. et al. The albedo-color diversity of transneptunian objects. *Astrophys. J. Lett.* **793**, L2 (2014).

10. Peixinho, N., Delsanti, A. & Doressoundiram, A. Reanalyzing the visible colors of Centaurs and KBOs: what is there and what we might be missing. *Astron. Astrophys.* **577**, A35 (2015).

11. Marssset, M. et al. Col-OSSOS: evidence for a compositional gradient inherited from the protoplanetary disk? *Planet. Sci. J.* **4**, 160 (2023).

12. Brown, M. E. The compositions of Kuiper Belt objects. *Annu. Rev. Earth Planet. Sci.* **40**, 467–494 (2012).

13. Pinilla-Alonso, N., Stansberry, J. A. & Holler, B. J. in *The Trans-Neptunian Solar System* (eds Prialnik, D. et al.) 395–412 (Elsevier, 2020).

14. McClure, M. K. et al. An Ice Age JWST inventory of dense molecular cloud ices. *Nat. Astron.* **7**, 431–443 (2023).

15. Altwegg, K., Balsiger, H. & Fuselier, S. A. Cometary chemistry and the origin of icy Solar System bodies: the view after Rosetta. *Annu. Rev. Astron. Astrophys.* **57**, 113–155 (2019).

16. Biver, N., Dello Russo, N., Opitom, C. & Rubin, M. Chemistry of comet atmospheres. Preprint at https://arxiv.org/abs/2207.04800 (2022).

17. Pinto, O. H. et al. First detection of CO₂ emission in a Centaur: JWST NIRSpec observations of 39P/Oterma. *Planet. Sci. J.* **4**, 208 (2023).

18. Pinilla-Alonso, N. et al. Unveiling the ice and gas nature of active Centaur (2060) Chiron using the James Webb Space Telescope. Preprint at https://arxiv.org/abs/2407.07761 (2024).

19. Pinilla-Alonso et al. DiSco-TNOs: discovering the surface composition of the trans-Neptunian objwects, icy embryos for planet formation. JWST Proposal Cycle 1, ID #2418 (2021); https://ui.adsabs.harvard.edu/abs/2021jwst.prop.2418P/abstract

20. Licandro, J. et al. Thermal evolution of trans-Neptunian objects through observations of Centaurs with JWST. *Nat. Astron.* https://doi.org/10.1038/s41550-024-02417-2 (2024).

21. Böker, T. et al. The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope. III. Integral-field spectroscopy. *Astron. Astrophys.* **661**, A82 (2022).

22. Topiak, M. et al. Quasars/orange-spectroscopy: Release 0.5.8. (2021); https://doi.org/10.5281/zenodo.1188775

23. Pendleton, Y. J. & Allamandola, L. J. The organic refractory material in the diffuse interstellar medium: mid-infrared spectroscopic constraints. *Astrophys. J. Suppl. Ser.* **138**, 75–98 (2002).

24. Palumbo, M. E., Castorina, A. C. & Strazzulla, G. Ion irradiation effects on frozen methanol (CH₃OH). *Astron. Astrophys.* **342**, 551–562 (1999).

25. Vernazza, P. et al. Interplanetary dust particles as samples of icy asteroids. *Astrophys. J.* **806**, 204 (2015).

26. Ciarniello, M. et al. VIS-IR spectroscopy of mixtures of water ice, organic matter, and opaque mineral in support of small body remote sensing observations. *Minerals* **11**, 1222 (2021).

27. De Prá, M. N. et al. Widespread CO₂ and CO ices in the trans-Neptunian population revealed by JWST/DiSco-TNOs. *Nat. Astron.* https://doi.org/10.1038/s41550-024-02276-x (2024).

28. Bergin, E. A., Blake, G. A., Ciesla, F., Hirschmann, M. M. & Li, J. Tracing the ingredients for a habitable Earth from interstellar space through planet formation. *Proc. Natl Acad. Sci. USA* **112**, 8965–8970 (2015).

29. Grundy, W. M. et al. Color, composition, and thermal environment of Kuiper Belt object (486958) Arrokoth. *Science* **367**, aay3705 (2020).

30. Gomes, R., Levison, H. F., Tsiganis, K. & Morbidelli, A. Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets. *Nature* **435**, 466–469 (2005).

31. Morbidelli, A., Levison, H. F., Tsiganis, K. & Gomes, R. Chaotic capture of Jupiter's Trojan asteroids in the early Solar System. *Nature* **435**, 462–465 (2005).

32. Tsiganis, K., Gomes, R., Morbidelli, A. & Levison, H. F. Origin of the orbital architecture of the giant planets of the Solar System. *Nature* **435**, 459–461 (2005).

33. Brasser, R., Schwamb, M. E., Lykawka, P. S. & Gomes, R. S. An Oort cloud origin for the high-inclination, high-perihelion Centaurs. *Mon. Not. R. Astron. Soc.* **420**, 3396–3402 (2012).

34. Szabó, G. M. et al. Surface ice and tholins on the extreme Centaur 2012 DR₃₀. *Astron. J.* **155**, 170 (2018).

35. Morbidelli, A., Batygin, K., Brasser, R. & Raymond, S. N. No evidence for interstellar planetesimals trapped in the Solar System. *Mon. Not. R. Astron. Soc.* **497**, L46–L49 (2020).

36. Rothard, H. et al. Modification of ices by cosmic rays and solar wind. *J. Phys. B* **50**, 062001 (2017).
37. Loeffler, M. J., Baratta, G. A., Palumbo, M. E., Strazzulla, G. & Baragiola, R. A. CO₂ synthesis in solid CO by Lyman-α photons and 200 keV protons. *Astron. Astrophys.* **435**, 587–594 (2005).

38. Gomis, O., Satorre, M. A., Strazzulla, G. & Leto, G. Hydrogen peroxide formation by ion implantation in water ice and its relevance to the Galilean satellites. *Planet. Space Sci.* **52**, 371–378 (2004).

39. Quirico, E. et al. On a radiolytic origin of red organics at the surface of the Arrokoth trans-Neptunian object. *Icarus* **394**, 115396 (2023).

40. Brunetto, R., Barucci, M. A., Dotto, E. & Strazzulla, G. Ion irradiation of frozen methanol, methane, and benzene: linking to the colors of Centaurs and trans-Neptunian objects. *Astrophys. J.* **644**, 646–650 (2006).

41. Moore, M. H., Ferrante, R., Hudson, R. & Stone, J. Ammonia-water ice laboratory studies relevant to outer Solar System surfaces. *Icarus* **190**, 260–273 (2007).

42. Bockelée-Morvan, D. et al. Comet 67P outbursts and quiescent coma at 1.3 au from the Sun: dust properties from Rosetta/VIRTIS-H observations. *Mon. Not. R. Astron. Soc.* **469**, S443–S458 (2017).

43. Poston, M. J. et al. Visible near-infrared spectral evolution of irradiated mixed ices and application to Kuiper Belt objects and Jupiter Trojans. *Astrophys. J.* **856**, 124 (2018).

44. Buchanan, L. E. et al. Col-OSSOS: probing ice line/color transitions within the Kuiper Belt's progenitor populations. *Planet. Sci. J.* **3**, 9 (2022).

45. Wood, B. E., Redfield, S., Linsky, J. L. & Sahu, M. S. Elemental abundances and ionization states within the local interstellar cloud derived from Hubble Space Telescope and far ultraviolet spectroscopic explorer observations of the Capella line of sight. *Astrophys. J.* **581**, 1168–1179 (2002).

46. Montmerle, T. et al. From Suns to life: a chronological approach to the history of life on Earth. 3. Solar System formation and early evolution: the first 100 million years. *Earth Moon Planets* **98**, 39–95 (2006).

47. Gordon, K. D. et al. The James Webb Space Telescope absolute flux calibration. I. Program design and calibrator stars. *Astron. J.* **163**, 267 (2022).

48. Souza-Feliciano, A. C. et al. Spectroscopy of the binary TNO Mors-Somnus with the JWST and its relationship to the cold classical and plutino subpopulations observed in the DiSCo-TNO project. *Astron. Astrophys.* **681**, L17 (2024).

49. Müller, T., Lellouch, E. & Fornasier, S. Trans-Neptunian objects and Centaurs at thermal wavelengths. In *The Trans-Neptunian Solar System* (eds Prialnik, D. et al.) 153–181 (Elsevier, 2020).

50. Volk, K. & Van Laerhoven, C. Dynamical classifications of multi-opposition TNOs as of 2023 December. *Res. Notes AAS* **8**, 36 (2024).

51. Gladman, B., Marsden, B. G. & Vanlaerhoven, C. in *The Solar System Beyond Neptune* (eds Barucci, M. A. et al.) 43–57 (Univ. Arizona Press, 2008).

52. de la Fuente Marcos, C. & de la Fuente Marcos, R. Large retrograde Centaurs: visitors from the Oort cloud? *Astrophys. Space Sci.* **352**, 409–419 (2014).

53. Licandro, J., di Fabrizio, L., Pinilla-Alonso, N., de León, J. & Oliva, E. Trans-Neptunian object (55636) 2002 TX₃₀₀, a fresh icy surface in the outer Solar System. *Astron. Astrophys.* **457**, 329–333 (2006).

54. Brown, M. E., Barkume, K. M., Ragozzine, D. & Schaller, E. L. A collisional family of icy objects in the Kuiper Belt. *Nature* **446**, 294–296 (2007).

55. Pinilla-Alonso, N., Licandro, J., Gil-Hutton, R. & Brunetto, R. The water ice rich surface of (145453) 2005 RR₄₃: a case for a carbon-depleted population of TNOs? *Astron. Astrophys.* **468**, L25–L28 (2007).

56. Pinilla-Alonso, N., Licandro, J. & Lorenzi, V. Visible spectroscopy in the neighborhood of 2003EL{61}. *Astron. Astrophys.* **489**, 455–458 (2008).

57. Pinilla-Alonso, N. et al. The surface of (136108) Haumea (2003 EL{61}), the largest carbon-depleted object in the trans-Neptunian belt. *Astron. Astrophys.* **496**, 547–556 (2009).

58. Toplak, M. et al. Infrared orange: connecting hyperspectral data with machine learning. *Synchrotron Radiat. News* **30**, 40–45 (2017).

59. Savitzky, A. & Golay, M. J. E. Smoothing and differentiation of data by simplified least squares procedures. *Anal. Chem.* **36**, 1627–1639 (1964).

60. Rousseeuw, P. J. Silhouettes: a graphical aid to the interpretation and validation of cluster analysis. *J. Comput. Appl. Math.* **20**, 53–65 (1987).

61. Tan, P., Steinbach, M. & Kumar, V. *Introduction to Data Mining: Pearson New International Edition* PDF eBook (Pearson Education, 2013).

62. Weyer, L. G. Near-infrared spectroscopy of organic substances. *Appl. Spectrosc. Rev.* **21**, 1–43 (1985).

63. Mastrapa, R. M., Grundy, W. M. & Gudipati, M. S. Amorphous and crystalline H₂O ice. In *The Science of Solar System Ices. Astrophysics and Space Science Library* Vol. 356 (eds Gudipati, M. S. & Castillo-Rogez, J.) 371 (Springer, 2013).

64. Villanueva, G. L. et al. JWST molecular mapping and characterization of Enceladus’ water plume feeding its torus. *Nat. Astron.* **7**, 1056–1062 (2023).

65. Hansen, G. B. & McCord, T. B. Amorphous and crystalline ice on the Galilean satellites: a balance between thermal and radiolytic processes. *J. Geophys. Res. E: Planets* **109**, E01012 (2004).

66. Grundy, W. & Schmitt, B. The temperature-dependent near-infrared absorption spectrum of hexagonal H₂O ice. *J. Geophys. Res.* **103**, 25809–25822 (1998).

67. Mastrapa, R. M., Sandford, S. A., Roush, T. L., Cruikshank, D. P. & Dalle Ore, C. M. Optical constants of amorphous and crystalline H₂O-ice: 2.5–22 µm (4000–455 cm⁻¹) optical constants of H₂O-ice. *Astrophys. J.* **701**, 1347–1356 (2009).

68. Leto, G. & Baratta, G. A. Ly-α photon induced amorphization of Ic water ice at 16 Kelvin. Effects and quantitative comparison with ion irradiation. *Astron. Astrophys.* **397**, 7–13 (2003).

69. Barucci, M. A. et al. New insights on ices in Centaur and Transneptunian populations. *Icarus* **214**, 297–307 (2011).

70. Sandford, S. A. & Allamandola, L. J. The physical and infrared spectral properties of CO₂ in astrophysical ice analogs. *Astrophys. J.* **355**, 357–372 (1990).

71. Sandford, S., Allamandola, L., Tielens, A. & Valero, G. Laboratory studies of the infrared spectral properties of CO in astrophysical ices. *Astrophys. J.* **329**, 498–510 (1988).

72. Lisse, C. et al. On the origin & thermal stability of Arrokoth's and Pluto's ices. *Icarus* **356**, 114072 (2021).

73. Cruikshank, D. P. et al. The composition of Centaur 5145 Pholus. *Icarus* **135**, 389–407 (1998).

74. Urso, R. G., Baklouti, D., Djouadi, Z., Pinilla-Alonso, N. & Brunetto, R. Near-infrared methanol bands probe energetic processing of icy outer Solar System objects. *Astrophys. J. Lett.* **894**, L3 (2020).

75. Barucci, M. A., Merlin, F., Dotto, E., Doressoundiram, A. & de Bergh, C. TNO surface ices. Observations of the TNO 55638 (2002 VE₉₅) and analysis of the population's spectral properties. *Astron. Astrophys.* **455**, 725–730 (2006).

76. Grim, R., Baas, F., Geballe, T., Greenberg, J. & Schutte, W. Detection of solid methanol toward W33A. *Astron. Astrophys.* **243**, 473–477 (1991).

77. Fayolle, M. et al. Testing tholins as analogues of the dark reddish material covering Pluto's Cthulhu region. *Icarus* **367**, 114574 (2021).
78. Nna-Mvondo, D., Khare, B. N., Ruiz-Bermejo, M. & McKay, C. P. Reactivity of tholins on Titan's surface under impact shock processes: a laboratory approach. In *European Planetary Science Congress 2012* EPSC2012-237 (2012).

79. Beć, K. B., Grabska, J., Badzoka, J. & Huck, C. W. Spectra-structure correlations in NIR region of polymers from quantum chemical calculations. The cases of aromatic ring, C=O, C≡N and C-Cl functionalities. *Spectrochim. Acta A* **262**, 120085 (2021).

80. Moroz, L., Arnold, G., Korochantsev, A. & Wäsch, R. Natural solid bitumens as possible analogs for cometary and asteroid organics: 1. Reflectance spectroscopy of pure bitumens. *Icarus* **134**, 253–268 (1998).

81. Quirico, E. et al. Refractory and semi-volatile organics at the surface of comet 67p/Churyumov-Gerasimenko: insights from the VIRTIS/Rosetta imaging spectrometer. *Icarus* **272**, 32–47 (2016).

82. Cruikshank, D. P. et al. Solid CN bearing material on outer Solar System bodies. *Icarus* **94**, 345–353 (1991).

83. Pendleton, Y., Tielens, A., Tokunaga, A. & Bernstein, M. The interstellar 4.62 micron band. *Astrophys. J.* **513**, 294–304(1999).

84. Baratta, G. et al. Organic samples produced by ion bombardment of ices for the EXPOSE-R2 mission on the International Space Station. *Planet. Space Sci.* **118**, 211–220 (2015).

85. McCord, T. A. et al. Organics and other molecules in the surfaces of Callisto and Ganymede. *Science* **278**, 271–275 (1997).

86. Mahjoub, A. et al. Complex organosulfur molecules on comet 67P: evidence from the ROSINA measurements and insights from laboratory simulations. *Sci. Adv.* **9**, eadh0394 (2023).

87. Ferrante, R. F., Moore, M. H., Spiliotis, M. M. & Hudson, R. L. Formation of interstellar OCS: radiation chemistry and IR spectra of precursor ices. *Astrophys. J.* **684**, 1210 (2008).

88. Palumbo, M., Geballe, T. & Tielens, A. G. Solid carbonyl sulfide (OCS) in dense molecular clouds. *Astrophys. J.* **479**, 839–844 (1997).

89. Cochran, A. L. et al. The composition of comets. *Space Sci. Rev.* **197**, 9–46 (2015).

90. Bockelée-Morvan, D. et al. Evolution of CO₂, CH₄, and OCS abundances relative to H₂O in the coma of comet 67P around perihelion from Rosetta/VIRTIS-H observations. *Mon. Not. R. Astron. Soc.* **462**, S170–S183 (2016).

91. Bennett, C. J., Jamieson, C. S. & Kaiser, R. I. Mechanical studies on the formation and destruction of carbon monoxide (CO), carbon dioxide (CO₂), and carbon trioxide (CO₃) in interstellar ice analog samples. *Phys. Chem. Chem. Phys.* **12**, 4032–4050 (2010).

92. Hudson, R. L. & Gerakines, P. A. Infrared spectra and interstellar sulfur: new laboratory results for H₂S and four malodorous thiol ices. *Astrophys. J.* **867**, 138 (2018).

93. Calmonte, U. et al. Sulphur-bearing species in the coma of comet 67P/Churyumov-Gerasimenko. *Mon. Not. R. Astron. Soc.* **462**, S253–S273 (2016).

94. Nash, D. B. & Betts, B. H. Laboratory infrared spectra (2.3-23 µm) of SO₂ phases: applications to lo surface analysis. *Icarus* **117**, 402–419 (1995).

95. Mahjoub, A. et al. Effect of H₂S on the near-infrared spectrum of irradiation residue and applications to the Kuiper Belt object (486958) Arrokoth. *Astrophys. J. Lett.* **914**, L31 (2021).

96. Kremer, C., Mustard, J. & Pieters, C. Cross-over infrared spectroscopy: a new tool for the remote determination of olivine composition. *Geophys. Res. Lett.* **47**, e2020GL089151 (2020).

97. Mastrapa, R. M. E. Optical constants and lab spectra of water ice V1.0. NASA *Planetary Data System* https://ui.adsabs.harvard.edu/abs/2010PDSS.126....M (2010)

98. Nna-Mvondo, D. NIR and MIR reflectance spectra of AMES tholins (from 90%:10% gas). *SSHADE/SOSYPOL* (OSUG Data Center) https://doi.org/10.26302/SSHADE/EXPERIMENT_[DM_20121002_004 (2018).

99. Yarnall, Y. Y. & Hudson, R. L. A new method for measuring infrared band strengths in H₂O ices: first results for OCS, H₂S, and SO₂. *Astrophys. J. Lett.* **931**, L4 (2022).

100. Ehrenfreund, P., Boogert, A. C. A., Gerakines, P. A., Tielens, A. G. G. M. & van Dishoeck, E. F. Infrared spectroscopy of interstellar apolar ice analogs. *Astron. Astrophys.* **328**, 649–669 (1997).

101. van Broekhuizen, F. A., Keane, J. V. & Schutte, W. A. A quantitative analysis of OCN⁻ formation in interstellar ice analogs. *Astron. Astrophys.* **415**, 425–436 (2004).

102. Fray, N. & Bouilloud, M. MIR absorbance spectra of CO ice at 25K for different deposition rates and different thicknesses. *SSHADE/SOSYPOL (OSUG Data Center) https://doi.org/10.26302/SSHADE/EXPERIMENT_NF_20180503_2100 (2012).*

103. Hainaut, O. R., Boehnhardt, H. & Protopapa, S. Colours of minor bodies in the outer Solar System. II. A statistical analysis revisited. *Astron. Astrophys.* **546**, A115 (2012).

104. Sheppard, S. S., Ragozzine, D. & Trujillo, C. 2007 TY430: a cold classical Kuiper Belt type binary in the Plutino population. *Astron. J.* **143**, 58 (2012).

105. Bauer, J. M. et al. Centaurs and scattered disk objects in the thermal infrared: analysis of WISE/NEOWISE observations. *Astrophys. J.* **773**, 22 (2013).

106. Tegler, S. C., Romanishin, W. & Consolmagno, G. J. Two color populations of Kuiper Belt and Centaur objects and the smaller orbital inclinations of red Centaur objects. *Astron. J.* **152**, 210 (2016).

107. Lorenzi, V. et al. Visible and NIR spectroscopy of (468861) 2013 LU28 with TNG. In *Proc. Asteroids, Comets, Meteors Conference 2023* (LPI, 2023); https://www.hou.usra.edu/meetings/acm2023/pdf/2379.pdf

## Acknowledgements

The DiSco-TNOs team would like to thank W. Eck and A. Henry of the Space Telescope Science Institute (STScI) for their help in preparing the observations for execution. This study was based on observations made with the National Aeronautics and Space Administration/ European Space Agency/Canadian Space Agency JWST under the GO-1 programme 2418. Support for this programme was provided by NASA through a grant from STScI. The data were obtained from the Barbara A. Mikulski Archive for Space Telescopes at the STScI, which is operated by the Association of Universities for Research in Astronomy, under the NASA contract NAS 5-03127 for JWST. N.P.-A. acknowledges the Ministry of Science, Innovation, and Universities (MCIU) in Spain and the State Agency for Research (AEI) for funding through the ATRAE programme, project ATR2023-145683. R.B. and E.H. acknowledge the support from the CNES-France (JWST mission). N.P. acknowledges funding by Fundação para a Ciência e a Tecnologia through the research grants UIDB/04434/2020 and UIDP/04434/2020. J.A.S. acknowledges the Lowell Observatory and Northern Arizona University, both in Flagstaff, AZ, for their support during his sabbatical tenure. J.L. acknowledges support from the ACIISI, Consejería de Economía, Conocimiento y Empleo del Gobierno de Canarias and the European Regional Development Fund under grant ProID2021010134, and support from the Agencia Estatal de Investigación del Ministerio de Ciencia e Innovación under grant 'Hydrated Minerals and Organic Compounds in Primitive Asteroids' with reference PID2020-120464GB-100.

## Author contributions

N.P.-A., V.L., M.N.D.P., B.J.H. and J.A.S. designed the observational programme. N.P.-A., R.B., M.N.D.P., J.L., Y.J.P., D.P.C., T.G.M., J.A.S. and J.P.E. conceived the scientific goals of DiSco. B.H., N.P.-A., I.W., A.C.d.S.F., M.N.D.P. and C.A.S. reduced and validated the data. N.P.-A., E.H., R.B., M.N.D.P., A.C.d.S.F., J.A.S. and T.G.M. performed the band identification and spectral characterization. R.B., M.N.D.P. and N.P.-A.
performed clustering and studied the band areas. R.B., N.P.-A. and B.J.H. elaborated and proposed the scenario for interpreting the results. N.P.-A., R.B. and E.H. drafted the manuscript. All authors were involved in the discussion of the results and the finalization of the manuscript.

**Competing interests**

The authors declare no competing interests.

**Additional information**

**Extended data** is available for this paper at
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https://doi.org/10.1038/s41550-024-02433-2.

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Noemí Pinilla-Alonso.

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2024

Noemí Pinilla-Alonso<sup>1,2✉</sup>, Rosario Brunetto<sup>3</sup>, Mário N. De Prá<sup>1</sup>, Bryan J. Holler<sup>3</sup>,<sup>4</sup> Elsa Hénault<sup>3</sup>, Ana Carolina de Souza Feliciano<sup>1</sup>, Vania Lorenzi<sup>5,6</sup>, Yvonne J. Pendleton<sup>7</sup>, Dale P. Cruikshank<sup>6</sup>,<sup>7</sup> Thomas G. Müller<sup>8</sup>, John A. Stansberry<sup>4,9,10</sup>, Joshua P. Emery<sup>6</sup>,<sup>9</sup> Charles A. Schambeau<sup>1</sup>, Javier Licandro<sup>6,11</sup>, Brittany Harvison<sup>1</sup>, Lucas McClure<sup>9</sup>, Aurélie Guilbert-Lepoutre<sup>12</sup>, Nuno Peixinho<sup>13</sup>, Michele T. Bannister<sup>14</sup> & Ian Wong<sup>6</sup>

<footnote n="1">¹Florida Space Institute, University of Central Florida, Orlando, FL, USA. ²Institute of Space Science and Technology of Asturias (ICTEA), Universidad de Oviedo, Oviedo, Spain. ³Université Paris-Saclay, CNRS, Institut d'Astrophysique Spatiale, Orsay, France. ⁴Space Telescope Science Institute, Baltimore, MD, USA. ⁵Fundación Galileo Galilei-INAF, La Palma, Spain. ⁶Instituto de Astrofísica de Canarias, La Laguna, Spain. ⁷Department of Physics, University of Central Florida Orlando, FL, USA. ⁸Max-Planck-Institut für Extraterrestrische Physik, Garching, Germany. ⁹Northern Arizona University, Flagstaff, AZ, USA. ¹⁰Lowell Observatory, Flagstaff, AZ, USA. ¹¹Departamento de Astrofísica, Universidad de La Laguna, La Laguna, Spain. ¹²Laboratoire de Géologie de Lyon: Terre, Planètes, Environnement, CNRS UCBL, ENSL, Villeurbanne, France. ¹³Instituto de Astrofísica e Ciências do Espaço, Departamento de Física, Universidade de Coimbra, Coimbra, Portugal. ¹⁴Te Kura Matū School of Physical and Chemical Sciences, University of Canterbury Christchurch, New Zealand. ✉e-mail: npinilla@ucf.edu</footnote>
<figure><img src="image_9.png" /><figcaption>**Extended Data Fig. 1 | Bowl-type DISCO spectra.** All the spectra in the Bowl-type group normalized at 2.6 µm and shifted vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>**Extended Data Fig. 2** | Double Dip-type DiSCo spectra. All the spectra in the Double-Dip-type group normalized at 2.6 µm and shift vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.</figcaption></figure>
<figure><img src="image_11.png" /></figure>

**Extended Data Fig. 3** | **Cliff-type DISCO spectra.** All the spectra in the Cliff-type group normalized at 2.6 µm and shift vertically for clarity. The error bar at each wavelength, corresponding to the standard deviation, is represented in grey.
<figure><img src="image_12.png" /></figure>

**Extended Data Fig. 4 | Unclassified DiSCo Spectra.** Spectra of objects in the DiSCo sample not included in the clustering corresponding, from top to bottom, to two low signal-to-noise observations, five Centaurs, and one object in the Haumea family. The Centaurs are studied in detail in$^{20}$. The spectrum of 2013 UZ$_{117}$ does not resemble any other object in the DiSCo sample but it is in agreement

with the spectra of other objects in the Haumea family observed in program GTO-1191. Its peculiar shape resembles that of pure water ice making these objects the only water-ice-rich surfaces in the trans-Neptunian belt. Spectra have been normalized at 2.6 µm and shifted vertically for clarity. The light grey bars at each wavelength correspond to the standard deviation.
<figure><img src="image_13.png" /><figcaption>Euclidean distance metric</figcaption></figure>

<table><thead><tr><th>Object</th><th>Obs. ID</th></tr></thead><tbody><tr><td>1995TL8</td><td>39</td></tr><tr><td>2010VZ98</td><td>15</td></tr><tr><td>2004PF115</td><td>19</td></tr><tr><td>2004PG115</td><td>20</td></tr><tr><td>2002TC302</td><td>13</td></tr><tr><td>2007JF43</td><td>29</td></tr><tr><td>2005PU21</td><td>40</td></tr><tr><td>Mors</td><td>45</td></tr><tr><td>2001QD298</td><td>59</td></tr><tr><td>Sila-Nunam</td><td>43</td></tr><tr><td>Lempo</td><td>6</td></tr><tr><td>Somnus</td><td>45</td></tr><tr><td>Kagara</td><td>57</td></tr><tr><td>Borasisi</td><td>56</td></tr><tr><td>1999OX3</td><td>104</td></tr><tr><td>2003GH55</td><td>58</td></tr><tr><td>Huya</td><td>3</td></tr><tr><td>2000OK67</td><td>51</td></tr><tr><td>2014LV28</td><td>42</td></tr><tr><td>2010ER65</td><td>46</td></tr><tr><td>2014YF50</td><td>30</td></tr><tr><td>2008NW4</td><td>36</td></tr><tr><td>2005TB190</td><td>25</td></tr><tr><td>2010ET65</td><td>44</td></tr><tr><td>2003UY413</td><td>153</td></tr><tr><td>1999DE9</td><td>21</td></tr><tr><td>2002UX25</td><td>7</td></tr><tr><td>2004TY364</td><td>12</td></tr><tr><td>2005RN43</td><td>11</td></tr><tr><td>2004XA192</td><td>9</td></tr><tr><td>2005QU182</td><td>133</td></tr><tr><td>2003FY128</td><td>116</td></tr><tr><td>G!kún||'hòmdímà</td><td>2</td></tr><tr><td>Dziewanna</td><td>5</td></tr><tr><td>2004UX10</td><td>114</td></tr><tr><td>2010VW11</td><td>31</td></tr><tr><td>Varda</td><td>10</td></tr><tr><td>2001FZ173</td><td>47</td></tr><tr><td>1996TL66</td><td>34</td></tr><tr><td>2003UZ413</td><td>27</td></tr><tr><td>2002XV93</td><td>22</td></tr><tr><td>2004NT33</td><td>24</td></tr><tr><td>2013LU28</td><td>1</td></tr><tr><td>2007RW10</td><td>50</td></tr><tr><td>2004EW95</td><td>18</td></tr><tr><td>1998SN165</td><td>32</td></tr><tr><td>Typhon</td><td>41</td></tr><tr><td>2005CC79</td><td>48</td></tr><tr><td>2012DR30</td><td>54</td></tr><tr><td>2015SO20</td><td>52</td></tr><tr><td>2001FP185</td><td>55</td></tr></tbody></table>

<figure><img src="image_14.png" /><figcaption>Cosine distance metric</figcaption></figure>

<table><thead><tr><th>Object</th><th>Obs. ID</th></tr></thead><tbody><tr><td>2004PG115</td><td>20</td></tr><tr><td>2002TC302</td><td>13</td></tr><tr><td>2007JF43</td><td>29</td></tr><tr><td>2010VZ98</td><td>15</td></tr><tr><td>2004PF115</td><td>19</td></tr><tr><td>1995TL8</td><td>39</td></tr><tr><td>2001QD298</td><td>59</td></tr><tr><td>Mors</td><td>45</td></tr><tr><td>Sila-Nunam</td><td>43</td></tr><tr><td>Lempo</td><td>6</td></tr><tr><td>2005PU21</td><td>40</td></tr><tr><td>Somnus</td><td>45</td></tr><tr><td>Kagara</td><td>57</td></tr><tr><td>Borasisi</td><td>56</td></tr><tr><td>1999OX3</td><td>104</td></tr><tr><td>2003GH55</td><td>58</td></tr><tr><td>Huya</td><td>3</td></tr><tr><td>2000OK67</td><td>51</td></tr><tr><td>2005TB190</td><td>25</td></tr><tr><td>2010ET65</td><td>44</td></tr><tr><td>2014YF50</td><td>30</td></tr><tr><td>2008NW4</td><td>36</td></tr><tr><td>2014LV28</td><td>42</td></tr><tr><td>2010ER65</td><td>46</td></tr><tr><td>2003UY413</td><td>153</td></tr><tr><td>1999DE9</td><td>21</td></tr><tr><td>2002UX25</td><td>7</td></tr><tr><td>2004TY364</td><td>12</td></tr><tr><td>2005RN43</td><td>11</td></tr><tr><td>2004XA192</td><td>9</td></tr><tr><td>2005QU182</td><td>133</td></tr><tr><td>2003FY128</td><td>116</td></tr><tr><td>2004UX10</td><td>114</td></tr><tr><td>G!kún||'hòmdímà</td><td>2</td></tr><tr><td>2010VW11</td><td>31</td></tr><tr><td>Dziewanna</td><td>5</td></tr><tr><td>Varda</td><td>10</td></tr><tr><td>2001FZ173</td><td>47</td></tr><tr><td>2013LU28</td><td>1</td></tr><tr><td>2007RW10</td><td>50</td></tr><tr><td>2004EW95</td><td>18</td></tr><tr><td>1998SN165</td><td>32</td></tr><tr><td>1996TL66</td><td>34</td></tr><tr><td>2004NT33</td><td>24</td></tr><tr><td>2002XV93</td><td>22</td></tr><tr><td>2003UZ413</td><td>27</td></tr><tr><td>Typhon</td><td>41</td></tr><tr><td>2005CC79</td><td>48</td></tr><tr><td>2012DR30</td><td>54</td></tr><tr><td>2015SO20</td><td>52</td></tr><tr><td>2001FP185</td><td>55</td></tr></tbody></table>

**Extended Data Fig. 5 | Hierarchical clustering on the DiSCo dataset.** The detection of three main spectral groups is evident using either a Euclidean (left) or cosine (right) distance metric.
<figure><img src="image_15.png" /><figcaption>(C)</figcaption></figure>

<figure><img src="image_16.png" /><figcaption>(E)</figcaption></figure>

<figure><img src="image_17.png" /></figure>

**Extended Data Fig. 6** | Detail of absorption bands identified in DiSCo-TNOs spectra. Panel A: median of each compositional group ± the median absolute deviation compared to the reflectance of pure crystalline water ice⁹⁷ and a Tholin rich in C–H and N–H molecules⁹⁸. In green the spectrum of Enceladus obtained with JWST⁶⁴. Panel B: median of the Bowl-type spectra ± the median absolute deviation, Enceladus⁶⁴, and pure crystalline water ice, all three showing the Fresnel Peak at 3.1 µm. Panel C: Spectra of Arrokoth²⁹, from New Horizons, and

<figure><img src="image_18.png" /><figcaption>(D)</figcaption></figure>

<figure><img src="image_19.png" /><figcaption>(F)</figcaption></figure>

<figure><img src="image_20.png" /></figure>

two DiSCo-TNOs targets compared with the spectrum of methanol and a tholin rich in N–H and C–H molecules⁹⁸. Panel D: Median spectra of the Double-Dip and Cliff-type TNOs ± the median absolute deviation compared to the reflectance of methanol and tholins⁹⁸. Panel E: Spectra of two DiSCo-TNOs targets compared to the spectrum of methanol and H₂S⁹⁹. Panel F: Spectra of two DiSCo-TNO targets compared to the spectrum of Jupiter's moon Callisto⁸⁵ showing an absorption of C≡N and the spectra of ¹³CO₂¹⁰⁰, OCN−¹⁰¹, and CO¹⁰².
<figure><img src="image_21.png" /></figure>

**Extended Data Fig. 7** | Examples of calculations of band areas for four different objects. Band A: CH₃OH and organics; B: CO₂; C: H₂O; D: aliphatic C--H. Error bars are provided for each spectrum (median absolute deviation over the 4-dithers within each wavelength bin), confirming these are significant

<figure><img src="image_22.png" /></figure>

detections. The three baseline calculations and corresponding areas are reported in dark gray for the linear baseline, gray for the second order polynomial function, and light gray for the third order polynomial function. See text for more details.
Extended Data Table 1 | Observation circumstances

<table><thead><tr><th>Number</th><th>Prov. desig.</th><th>Name</th><th>Obs ID</th><th>V<sub>mag</sub></th><th>UT start time</th><th>r (au)</th><th>Δ (au)</th><th>α (°)</th><th>T<sub>exp</sub> (sec)</th><th>Comments</th></tr></thead><tbody><tr><td>48639</td><td>1995 TL<sub>8</sub></td><td></td><td>39</td><td>21.69</td><td>2023-01-05 02:27:42</td><td>46.44</td><td>45.75</td><td>0.89</td><td>1517</td><td>Binary</td></tr><tr><td>15874</td><td>1996 TL<sub>66</sub></td><td></td><td>34</td><td>21.47</td><td>2022-11-02 05:39:52</td><td>38.95</td><td>38.26</td><td>1.08</td><td>1401</td><td>Binary</td></tr><tr><td>79360</td><td>1997 CS<sub>29</sub></td><td>Sila-Nunam</td><td>43</td><td>21.84</td><td>2022-11-22 17:48:26</td><td>43.43</td><td>43.37</td><td>1.32</td><td>2334</td><td></td></tr><tr><td>52872</td><td>1998 SG<sub>35</sub></td><td>Okyrhoe</td><td>28</td><td>21.40</td><td>2022-11-03 11:32:30</td><td>10.54</td><td>9.88</td><td>4.24</td><td>1401</td><td></td></tr><tr><td>35671</td><td>1998 SN<sub>165</sub></td><td></td><td>32</td><td>21.50</td><td>2022-12-12 15:42:26</td><td>37.21</td><td>36.59</td><td>1.21</td><td>1401</td><td></td></tr><tr><td>26375</td><td>1999 DE<sub>9</sub></td><td></td><td>21</td><td>21.19</td><td>2023-06-07 17:43:06</td><td>40.90</td><td>40.41</td><td>1.27</td><td>1167</td><td></td></tr><tr><td>44594</td><td>1999 OX<sub>3</sub></td><td></td><td>4</td><td></td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td><td>Skipped</td></tr><tr><td>44594</td><td>1999 OX<sub>3</sub></td><td></td><td>104</td><td>19.77</td><td>2023-08-28 22:31:50</td><td>17.61</td><td>17.22</td><td>3.11</td><td>700</td><td>Repeat</td></tr><tr><td>66652</td><td>1999 RZ<sub>253</sub></td><td>Borasisi</td><td>56</td><td>22.27</td><td>2022-11-05 05:06:02</td><td>42.49</td><td>41.79</td><td>0.97</td><td>2568</td><td>Binary</td></tr><tr><td>47171</td><td>1999 TC<sub>36</sub></td><td>Lempo</td><td>6</td><td>20.03</td><td>2023-01-22 11:02:08</td><td>30.84</td><td>30.54</td><td>1.77</td><td>817</td><td>Hierarchical triple</td></tr><tr><td>38628</td><td>2000 EB<sub>173</sub></td><td>Huya</td><td>3</td><td>19.66</td><td>2023-03-13 12:43:05</td><td>28.96</td><td>28.92</td><td>1.98</td><td>700</td><td>Binary</td></tr><tr><td>138537</td><td>2000 OK<sub>67</sub></td><td></td><td>51</td><td>22.36</td><td>2022-11-23 14:01:00</td><td>40.04</td><td>39.52</td><td>1.22</td><td>2568</td><td></td></tr><tr><td>82158</td><td>2001 FP<sub>185</sub></td><td></td><td>55</td><td>22.31</td><td>2023-08-10 17:27:42</td><td>39.20</td><td>39.24</td><td>1.49</td><td>2568</td><td></td></tr><tr><td>82155</td><td>2001 FZ<sub>173</sub></td><td></td><td>47</td><td>21.66</td><td>2023-03-13 20:20:16</td><td>34.09</td><td>33.57</td><td>1.46</td><td>2334</td><td></td></tr><tr><td>32532</td><td>2001 PT<sub>13</sub></td><td>Thereus</td><td>8</td><td>20.14</td><td>2023-01-17 01:30:31</td><td>11.73</td><td>11.09</td><td>3.84</td><td>817</td><td></td></tr><tr><td>523591</td><td>2001 QD<sub>298</sub></td><td></td><td>59</td><td>22.65</td><td>2023-06-12 15:48:43</td><td>42.15</td><td>42.13</td><td>1.40</td><td>2568</td><td></td></tr><tr><td>275809</td><td>2001 QY<sub>297</sub></td><td></td><td>49</td><td>22.30</td><td>2022-10-26 16:54:57</td><td>44.19</td><td>43.68</td><td>1.12</td><td>2568</td><td>Binary, MSA short</td></tr><tr><td>42355</td><td>2002 CR<sub>46</sub></td><td>Typhon</td><td>41</td><td>21.80</td><td>2023-02-14 07:04:13</td><td>24.56</td><td>24.51</td><td>2.33</td><td>2334</td><td>Binary</td></tr><tr><td>250112</td><td>2002 KY<sub>14</sub></td><td></td><td>38</td><td>21.78</td><td>2022-10-30 14:18:35</td><td>14.75</td><td>14.68</td><td>3.89</td><td>1401</td><td></td></tr><tr><td>84522</td><td>2002 TC<sub>302</sub></td><td></td><td>13</td><td>20.43</td><td>2023-01-02 05:39:03</td><td>43.47</td><td>42.88</td><td>1.07</td><td>934</td><td></td></tr><tr><td>55637</td><td>2002 UX<sub>25</sub></td><td></td><td>7</td><td>20.03</td><td>2023-01-22 06:25:41</td><td>39.93</td><td>39.62</td><td>1.36</td><td>817</td><td></td></tr><tr><td>612533</td><td>2002 XV<sub>93</sub></td><td></td><td>22</td><td>20.85</td><td>2022-11-03 13:26:18</td><td>38.13</td><td>37.64</td><td>1.32</td><td>1167</td><td></td></tr><tr><td>120132</td><td>2003 FY<sub>128</sub></td><td></td><td>16</td><td>21.07</td><td>2023-01-30 15:04:05</td><td>40.94</td><td>40.85</td><td>1.39</td><td>292</td><td>1 dither</td></tr><tr><td>120132</td><td>2003 FY<sub>128</sub></td><td></td><td>116</td><td>21.02</td><td>2023-03-02 06:58:02</td><td>40.95</td><td>40.37</td><td>1.15</td><td>1167</td><td>Repeat</td></tr><tr><td>385437</td><td>2003 GH<sub>55</sub></td><td></td><td>58</td><td>22.35</td><td>2023-07-22 14:45:03</td><td>41.28</td><td>40.75</td><td>1.23</td><td>2568</td><td></td></tr><tr><td>174567</td><td>2003 MW<sub>12</sub></td><td>Varda</td><td>10</td><td>20.27</td><td>2023-03-19 20:51:09</td><td>46.08</td><td>46.04</td><td>1.25</td><td>934</td><td>Binary</td></tr><tr><td>120181</td><td>2003 UR<sub>292</sub></td><td></td><td>35</td><td>21.89</td><td>2023-01-17 23:37:08</td><td>27.28</td><td>26.70</td><td>1.71</td><td>1401</td><td>Nearby star</td></tr><tr><td>523601</td><td>2003 UY<sub>413</sub></td><td></td><td>53</td><td></td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td><td>Skipped</td></tr><tr><td>523601</td><td>2003 UY<sub>413</sub></td><td></td><td>153</td><td>21.90</td><td>2023-08-19 15:00:52</td><td>42.62</td><td>42.33</td><td>1.32</td><td>2568</td><td>Repeat</td></tr><tr><td>416400</td><td>2003 UZ<sub>117</sub></td><td></td><td>26</td><td>21.27</td><td>2023-01-18 06:48:29</td><td>38.55</td><td>37.91</td><td>1.14</td><td>1051</td><td>3 dithers</td></tr><tr><td>455502</td><td>2003 UZ<sub>413</sub></td><td></td><td>27</td><td>21.01</td><td>2023-02-14 05:13:06</td><td>44.70</td><td>44.62</td><td>1.27</td><td>1401</td><td></td></tr><tr><td>136204</td><td>2003 WL<sub>7</sub></td><td></td><td>37</td><td>21.45</td><td>2022-11-23 12:04:32</td><td>17.45</td><td>17.43</td><td>3.28</td><td>1401</td><td></td></tr><tr><td>120216</td><td>2004 EW<sub>95</sub></td><td></td><td>18</td><td>21.17</td><td>2023-02-22 01:16:30</td><td>27.17</td><td>27.16</td><td>2.11</td><td>1167</td><td></td></tr><tr><td>444030</td><td>2004 NT<sub>33</sub></td><td></td><td>24</td><td>20.72</td><td>2022-12-06 14:03:59</td><td>39.69</td><td>39.72</td><td>1.44</td><td>—</td><td></td></tr><tr><td>175113</td><td>2004 PF<sub>115</sub></td><td></td><td>19</td><td>20.85</td><td>2022-11-03 15:16:41</td><td>41.59</td><td>41.06</td><td>1.18</td><td>1167</td><td></td></tr><tr><td>307982</td><td>2004 PG<sub>115</sub></td><td></td><td>20</td><td>21.12</td><td>2022-11-03 18:39:58</td><td>39.57</td><td>39.04</td><td>1.23</td><td>1167</td><td></td></tr><tr><td>120348</td><td>2004 TY<sub>364</sub></td><td></td><td>12</td><td>20.38</td><td>2023-01-01 17:17:27</td><td>38.68</td><td>38.14</td><td>1.24</td><td>934</td><td></td></tr><tr><td>144897</td><td>2004 UX<sub>10</sub></td><td></td><td>14</td><td>20.54</td><td>2023-01-22 11:48:05</td><td>39.47</td><td>39.18</td><td>1.39</td><td>467</td><td>2 dithers</td></tr><tr><td>144897</td><td>2004 UX<sub>10</sub></td><td></td><td>114</td><td>20.55</td><td>2023-08-28 23:32:52</td><td>39.49</td><td>39.25</td><td>1.44</td><td>934</td><td>Repeat</td></tr><tr><td>230965</td><td>2004 XA<sub>192</sub></td><td></td><td>9</td><td>19.95</td><td>2022-11-03 17:01:44</td><td>35.52</td><td>35.28</td><td>1.57</td><td>934</td><td></td></tr><tr><td>545293</td><td>2005 CC<sub>79</sub></td><td></td><td>48</td><td>21.70</td><td>2023-03-19 22:06:02</td><td>27.17</td><td>26.64</td><td>1.82</td><td>2334</td><td></td></tr><tr><td>469705</td><td>2005 EF<sub>298</sub></td><td>‡Kágára</td><td>57</td><td>22.36</td><td>2023-05-08 19:59:38</td><td>40.22</td><td>39.60</td><td>1.16</td><td>2568</td><td>Binary</td></tr><tr><td>469750</td><td>2005 PU<sub>21</sub></td><td></td><td>40</td><td>21.99</td><td>2022-11-23 15:25:37</td><td>34.59</td><td>33.95</td><td>1.28</td><td>2334</td><td></td></tr><tr><td>303775</td><td>2005 QU<sub>182</sub></td><td></td><td>33</td><td>21.34</td><td>2023-01-12 12:52:48</td><td>55.07</td><td>55.06</td><td>1.03</td><td>1401</td><td>MSA short</td></tr><tr><td>303775</td><td>2005 QU<sub>182</sub></td><td></td><td>133</td><td>21.35</td><td>2023-07-28 12:22:03</td><td>55.36</td><td>55.17</td><td>1.05</td><td>1401</td><td>Repeat</td></tr><tr><td>145452</td><td>2005 RN<sub>43</sub></td><td></td><td>11</td><td>19.91</td><td>2022-11-03 08:47:10</td><td>40.60</td><td>39.98</td><td>1.12</td><td>934</td><td></td></tr><tr><td>145480</td><td>2005 TB<sub>190</sub></td><td></td><td>25</td><td>21.35</td><td>2022-11-28 17:51:49</td><td>46.34</td><td>45.95</td><td>1.14</td><td>1401</td><td></td></tr><tr><td>444745</td><td>2007 JF<sub>43</sub></td><td></td><td>29</td><td>21.24</td><td>2023-03-05 23:08:38</td><td>36.50</td><td>36.48</td><td>1.57</td><td>1401</td><td></td></tr><tr><td>470316</td><td>2007 OC<sub>10</sub></td><td></td><td>23</td><td>21.02</td><td>2022-10-25 20:35:39</td><td>36.48</td><td>35.93</td><td>1.33</td><td>1167</td><td>MSA short</td></tr><tr><td>309239</td><td>2007 RW<sub>10</sub></td><td></td><td>50</td><td>21.89</td><td>2022-12-12 04:29:47</td><td>31.59</td><td>30.95</td><td>1.39</td><td>2568</td><td></td></tr><tr><td>341520</td><td>2007 TY<sub>430</sub></td><td>Mors-Somnus</td><td>45</td><td>21.66</td><td>2023-01-22 12:44:30</td><td>29.05</td><td>28.66</td><td>1.81</td><td>2334</td><td>Binary</td></tr><tr><td>229762</td><td>2007 UK<sub>126</sub></td><td>G'l'kún||'hòmdímà</td><td>2</td><td>19.80</td><td>2023-02-22 22:20:11</td><td>40.95</td><td>40.72</td><td>1.36</td><td>700</td><td>Binary</td></tr><tr><td>470596</td><td>2008 NW<sub>4</sub></td><td></td><td>36</td><td>21.57</td><td>2022-10-29 06:42:04</td><td>36.59</td><td>36.05</td><td>1.34</td><td>1401</td><td></td></tr><tr><td>471143</td><td>2010 EK<sub>139</sub></td><td>Dziewanna</td><td>5</td><td>19.72</td><td>2023-02-14 03:40:13</td><td>34.83</td><td>34.80</td><td>1.64</td><td>700</td><td></td></tr><tr><td>552555</td><td>2010 ER<sub>65</sub></td><td></td><td>46</td><td>21.57</td><td>2023-02-21 22:54:16</td><td>41.95</td><td>41.36</td><td>1.11</td><td>2334</td><td></td></tr><tr><td>471137</td><td>2010 ET<sub>65</sub></td><td></td><td>44</td><td>21.44</td><td>2023-01-13 18:05:14</td><td>40.01</td><td>39.93</td><td>1.42</td><td>2334</td><td></td></tr><tr><td>310071</td><td>2010 KR<sub>59</sub></td><td></td><td>17</td><td>21.18</td><td>2023-03-02 05:45:34</td><td>20.26</td><td>20.16</td><td>2.82</td><td>1167</td><td>Nearby star</td></tr><tr><td>471210</td><td>2010 VW<sub>11</sub></td><td></td><td>31</td><td>21.26</td><td>2023-01-18 07:45:38</td><td>36.80</td><td>36.19</td><td>1.23</td><td>1401</td><td></td></tr><tr><td>445473</td><td>2010 VZ<sub>98</sub></td><td></td><td>15</td><td>20.58</td><td>2023-01-05 03:34:19</td><td>34.66</td><td>33.96</td><td>1.18</td><td>1167</td><td></td></tr><tr><td>2012 DR<sub>30</sub></td><td></td><td></td><td>54</td><td>21.12</td><td>2023-03-03 01:09:31</td><td>23.57</td><td>23.63</td><td>2.42</td><td>2568</td><td></td></tr><tr><td>468861</td><td>2013 LU<sub>28</sub></td><td></td><td>1</td><td>18.18</td><td>2023-02-14 09:02:23</td><td>9.17</td><td>8.46</td><td>4.50</td><td>350</td><td></td></tr><tr><td>523722</td><td>2014 LV<sub>28</sub></td><td></td><td>42</td><td>21.43</td><td>2022-11-03 09:58:39</td><td>35.62</td><td>35.54</td><td>1.60</td><td>2334</td><td></td></tr><tr><td>523777</td><td>2014 YF<sub>50</sub></td><td></td><td>30</td><td>21.06</td><td>2023-01-13 19:37:38</td><td>35.72</td><td>35.12</td><td>1.28</td><td>1401</td><td></td></tr><tr><td>508338</td><td>2015 SO<sub>20</sub></td><td></td><td>52</td><td>22.10</td><td>2023-01-17 21:56:28</td><td>33.59</td><td>33.36</td><td>1.66</td><td>2568</td><td></td></tr></tbody></table>

Details of JWST observations, including exposure time and V-band magnitude.
Extended Data Table 2 | Physical properties of the TNOs in the DiSCo program

<table><thead><tr><th>Prov. desig.</th><th>Obs. ID</th><th>Hv</th><th>Diameter (km)</th><th>pv</th><th>S' [%/1000 Å]</th><th>Ref</th><th>SIR<sub>1</sub> [%/1000 Å]</th><th>SIR<sub>2</sub> [%/1000 Å]</th><th>Dyn. Class.</th><th>Group</th></tr></thead><tbody><tr><td>1995 TL<sub>8</sub></td><td>39</td><td>5.30 ± 0.06</td><td>244.0<sup>+82.0</sup><sub>-63.0</sub></td><td>0.231<sup>+0.189</sup><sub>-0.102</sub></td><td>23.17 ± 6.08</td><td>(1)</td><td>8.37 ± 0.22</td><td>1.11 ± 0.14</td><td>HC</td><td>Cliff</td></tr><tr><td>1996 TL<sub>66</sub></td><td>34</td><td>5.40 ± 0.12</td><td>339.0 ± 20.0</td><td>0.110<sup>+0.011</sup><sub>-0.015</sub></td><td>3.75 ± 3.46</td><td>(1)</td><td>0.68 ± 0.16</td><td>-0.29 ± 0.09</td><td>Scat</td><td>Bowl</td></tr><tr><td>1997 CS<sub>29</sub></td><td>43</td><td>5.60 ± 0.04</td><td>343.0 ± 42</td><td>0.090<sup>+0.027</sup><sub>-0.017</sub></td><td>28.39 ± 3.34</td><td>(1)</td><td>6.22 ± 0.16</td><td>-0.5 ± 0.09</td><td>CC</td><td>Cliff</td></tr><tr><td>1998 SG<sub>35</sub></td><td>28</td><td>11.07 ± 0.1</td><td>35.0 ± 3.0</td><td>0.056<sup>+0.012</sup><sub>-0.010</sub></td><td>11.27 ± 3.22</td><td>(1)</td><td>4.72 ± 0.15</td><td>1.45 ± 0.1</td><td>Centaur</td><td></td></tr><tr><td>1998 SN<sub>165</sub></td><td>32</td><td>5.70 ± 0.085</td><td>393.0<sup>+39.0</sup><sub>-38.0</sub></td><td>0.060<sup>+0.013</sup><sub>-0.014</sub></td><td>8.24 ± 4.91</td><td>(1)</td><td>3.11 ± 0.16</td><td>1.55 ± 0.09</td><td>HC</td><td>Bowl</td></tr><tr><td>1999 DE<sub>9</sub></td><td>21</td><td>5.20 ± 0.046</td><td>311.0<sup>+29.0</sup><sub>-32.0</sub></td><td>0.163<sup>+0.041</sup><sub>-0.026</sub></td><td>20.12 ± 2.25</td><td>(1)</td><td>4.55 ± 0.16</td><td>-0.21 ± 0.09</td><td>5:2 Res</td><td>Double-Dip</td></tr><tr><td>1999 OX<sub>3</sub></td><td>104</td><td>7.70 ± 0.092</td><td>135.0<sup>+13.0</sup><sub>-13.0</sub></td><td>0.081<sup>+0.018</sup><sub>-0.015</sub></td><td>32.26 ± 3.94</td><td>(1)</td><td>7.12 ± 0.17</td><td>-0.5 ± 0.1</td><td>Scat</td><td>Cliff</td></tr><tr><td>1999 RZ<sub>253</sub></td><td>56</td><td>6.10 ± 0.07</td><td>163.0<sup>+13.0</sup><sub>-13.0</sub></td><td>0.236<sup>+0.018</sup><sub>-0.077</sub></td><td>34.2 ± 3.9</td><td>(1)</td><td>5.31 ± 0.15</td><td>-0.7 ± 0.09</td><td>CC</td><td>Cliff</td></tr><tr><td>1999 TC<sub>36</sub></td><td>6</td><td>5.40 ± 0.1</td><td>393.1<sup>+25.2</sup><sub>-26.8</sub></td><td>0.079<sup>+0.013</sup><sub>-0.013</sub></td><td>32.06 ± 2.34</td><td>(1)</td><td>7.47 ± 0.14</td><td>0.07 ± 0.08</td><td>3:2 Res</td><td>Cliff</td></tr><tr><td>2000 EB<sub>173</sub></td><td>3</td><td>5.00 ± 0.03</td><td>458.0 ± 9.2</td><td>0.083 ± 0.004</td><td>21.89 ± 4.59</td><td>(1)</td><td>4.78 ± 0.17</td><td>-0.29 ± 0.09</td><td>3:2 Res</td><td>Double-Dip</td></tr><tr><td>2000 OK<sub>67</sub></td><td>51</td><td>6.50 ± 0.13</td><td>164.0<sup>+33.0</sup><sub>-45.0</sub></td><td>0.169<sup>+0.159</sup><sub>-0.052</sub></td><td>20.14 ± 4.59</td><td>(1)</td><td>5.11 ± 0.16</td><td>0.18 ± 0.11</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2001 FP<sub>185</sub></td><td>55</td><td>6.40 ± 0.07</td><td>332.0<sup>+31.0</sup><sub>-24.0</sub></td><td>0.046<sup>+0.007</sup><sub>-0.007</sub></td><td>18.28 ± 2.69</td><td>(1)</td><td>3.93 ± 0.18</td><td>2.41 ± 0.11</td><td>Scat</td><td>Bowl</td></tr><tr><td>2001 FZ<sub>173</sub></td><td>47</td><td>6.20</td><td>212</td><td>0.12</td><td>17.27 ± 1.84</td><td>(1)</td><td>3.74 ± 0.21</td><td>-0.22 ± 0.12</td><td>Scat</td><td>Double-Dip</td></tr><tr><td>2001 PT<sub>13</sub></td><td>8</td><td>9.40 ± 0.16</td><td>62.0 ± 3.0</td><td>0.083<sup>+0.016</sup><sub>-0.013</sub></td><td>9.48 ± 2.01</td><td>(1)</td><td>5.37 ± 0.2</td><td>2.32 ± 0.12</td><td>Centaur</td><td></td></tr><tr><td>2001 QD<sub>298</sub></td><td>59</td><td>6.70 ± 0.17</td><td>233.0<sup>+27.0</sup><sub>-30.0</sub></td><td>0.067<sup>+0.002</sup><sub>-0.014</sub></td><td>30.4 ± 8.33</td><td>(1)</td><td>5.63 ± 0.17</td><td>-0.61 ± 0.11</td><td>CC</td><td>Cliff</td></tr><tr><td>2001 QY<sub>297</sub></td><td>49</td><td>5.90 ± 0.31</td><td>229.0<sup>+22.0</sup><sub>-108.0</sub></td><td>0.152<sup>+0.439</sup><sub>-0.015</sub></td><td>24.41 ± 8.17</td><td>(1)</td><td>6.85 ± 0.4</td><td>-1.16 ± 0.23</td><td>CC</td><td>t-Cliff</td></tr><tr><td>2002 CR<sub>46</sub></td><td>41</td><td>7.70 ± 0.04</td><td>185.0 ± 7.0</td><td>0.044 ± 0.003</td><td>13.97 ± 3.01</td><td>(1)</td><td>5.88 ± 0.18</td><td>1.67 ± 0.1</td><td>Scat</td><td>Bowl</td></tr><tr><td>2002 KY<sub>14</sub></td><td>38</td><td>10.37 ± 0.07</td><td>47.0<sup>+3.0</sup><sub>-4.0</sub></td><td>0.057<sup>+0.011</sup><sub>-0.007</sub></td><td>33.42 ± 2.46</td><td>(1)</td><td>7.07 ± 0.16</td><td>-0.17 ± 0.1</td><td>Centaur</td><td></td></tr><tr><td>2002 TC<sub>302</sub></td><td>13</td><td>4.20 ± 0.1</td><td>584.1<sup>+105.6</sup><sub>-30.0</sub></td><td>0.115<sup>+0.047</sup><sub>-0.033</sub></td><td>29.33 ± 2.4</td><td>(1)</td><td>7.2 ± 0.18</td><td>0.65 ± 0.12</td><td>5:2 Res</td><td>Cliff</td></tr><tr><td>2002 UX<sub>25</sub></td><td>7</td><td>3.90 ± 0.02</td><td>697.2<sup>+23.0</sup><sub>-25.9</sub></td><td>0.107 ± 0.008</td><td>19.31 ± 2.44</td><td>(1)</td><td>4.38 ± 0.16</td><td>-0.11 ± 0.09</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2002 XV<sub>93</sub></td><td>22</td><td>5.40 ± 0.46</td><td>549.2<sup>+27.7</sup><sub>-23.0</sub></td><td>0.040<sup>+0.020</sup><sub>-0.015</sub></td><td>0.85 ± 2.06</td><td>(1)</td><td>1.91 ± 0.18</td><td>0.08 ± 0.09</td><td>3:2 Res</td><td>Bowl</td></tr><tr><td>2003 FY<sub>128</sub></td><td>116</td><td>5.10 ± 0.09</td><td>460.0 ± 21.0</td><td>0.079 ± 0.010</td><td>21.48 ± 3.46</td><td>(1)</td><td>3.89 ± 0.19</td><td>-0.26 ± 0.1</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2003 GH<sub>55</sub></td><td>58</td><td>6.40 ± 0.12</td><td>178.0<sup>+21.0</sup><sub>-26.0</sub></td><td>0.150<sup>+0.182</sup><sub>-0.031</sub></td><td>25.97 ± 5.6</td><td>(2)</td><td>7.33 ± 0.14</td><td>-0.34 ± 0.09</td><td>CC</td><td>Cliff</td></tr><tr><td>2003 MW<sub>12</sub></td><td>10</td><td>3.60 ± 0.05</td><td>792.0<sup>+91.0</sup><sub>-84.0</sub></td><td>0.102<sup>+0.024</sup><sub>-0.020</sub></td><td>17.11 ± 7.64</td><td>(1)</td><td>5.1 ± 0.15</td><td>0.41 ± 0.09</td><td>15:8 Res</td><td>Double-Dip</td></tr><tr><td>2003 UY<sub>413</sub></td><td>153</td><td>5.43</td><td>293</td><td>0.14</td><td>19.9 ± 0.9</td><td>(3)</td><td>4.11 ± 0.17</td><td>0.09 ± 0.1</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2003 UZ<sub>117</sub></td><td>26</td><td>5.20 ± 0.15</td><td>222.0<sup>+57.0</sup><sub>-52.0</sub></td><td>0.290<sup>+1.60</sup><sub>-0.015</sub></td><td>-2.1 ± 2</td><td>(4)</td><td>-3.01 ± 0.19</td><td>-4.88 ± 0.08</td><td>HC</td><td>Haumea Fam</td></tr><tr><td>2003 UZ<sub>413</sub></td><td>27</td><td>5.70 ± 0.3</td><td>670.0<sup>+84.0</sup><sub>-82.0</sub></td><td>0.070<sup>+0.012</sup><sub>-0.015</sub></td><td>6.64 ± 3.72</td><td>(1)</td><td>2.27 ± 0.16</td><td>0.52 ± 0.09</td><td>3:2 Res</td><td>Bowl</td></tr><tr><td>2003 WL<sub>7</sub></td><td>37</td><td>8.75 ± 0.16</td><td>105.0<sup>+6.0</sup><sub>-7.0</sub></td><td>0.053 ± 0.010</td><td>11.7 ± 2.06</td><td>(1)</td><td>5.51 ± 0.16</td><td>2.53 ± 0.14</td><td>Centaur</td><td></td></tr><tr><td>2004 EW<sub>95</sub></td><td>18</td><td>6.70 ± 0.35</td><td>291.1<sup>+20.3</sup><sub>-25.9</sub></td><td>0.044<sup>+0.021</sup><sub>-0.015</sub></td><td>1.71 ± 2.06</td><td>(1)</td><td>2.89 ± 0.17</td><td>1.76 ± 0.09</td><td>3:2 Res</td><td>Bowl</td></tr><tr><td>2004 NT<sub>33</sub></td><td>24</td><td>4.70 ± 0.11</td><td>423.0<sup>+87.0</sup><sub>-80.0</sub></td><td>0.125<sup>+0.069</sup><sub>-0.039</sub></td><td>2.54 ± 0.9</td><td>(3)</td><td>2.05 ± 0.15</td><td>0.13 ± 0.09</td><td>HC</td><td>Bowl</td></tr><tr><td>2004 PF<sub>115</sub></td><td>19</td><td>4.50 ± 0.25</td><td>468.2<sup>+38.6</sup><sub>-49.1</sub></td><td>0.123<sup>+0.033</sup><sub>-0.033</sub></td><td></td><td></td><td>8.62 ± 0.15</td><td>1.01 ± 0.09</td><td>HC</td><td>Cliff</td></tr><tr><td>2004 PG<sub>115</sub></td><td>20</td><td>5.01</td><td>334</td><td>0.1</td><td>25.42 ± 0.9</td><td>(3)</td><td>7.5 ± 0.16</td><td>1.09 ± 0.09</td><td>Scat</td><td>Cliff</td></tr><tr><td>2004 TY<sub>364</sub></td><td>12</td><td>4.50 ± 0.07</td><td>512.0<sup>+37.0</sup><sub>-40.0</sub></td><td>0.107<sup>+0.020</sup><sub>-0.015</sub></td><td>20.78 ± 3.17</td><td>(1)</td><td>4.34 ± 0.18</td><td>0.13 ± 0.1</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2004 UX<sub>10</sub></td><td>114</td><td>4.80 ± 0.16</td><td>398.1<sup>+32.6</sup><sub>-39.3</sub></td><td>0.141<sup>+0.044</sup><sub>-0.031</sub></td><td>20.23 ± 4.4</td><td>(1)</td><td>2.89 ± 0.17</td><td>-0.37 ± 0.09</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2004 XA<sub>192</sub></td><td>9</td><td>4.40 ± 0.63</td><td>339.0<sup>+120.0</sup><sub>-95.0</sub></td><td>0.260<sup>+0.340</sup><sub>-0.150</sub></td><td></td><td></td><td>4.21 ± 0.14</td><td>0.02 ± 0.09</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2005 CC<sub>79</sub></td><td>48</td><td>7.19</td><td>203</td><td>0.06</td><td></td><td></td><td>5.87 ± 0.18</td><td>2.09 ± 0.11</td><td>Scat</td><td>Bowl</td></tr><tr><td>2005 EF<sub>298</sub></td><td>57</td><td>6.40 ± 0.5</td><td>174.0<sup>+27.0</sup><sub>-32.0</sub></td><td>0.160<sup>+0.130</sup><sub>-0.070</sub></td><td></td><td></td><td>6.07 ± 0.19</td><td>-0.84 ± 0.1</td><td>CC</td><td>Cliff</td></tr><tr><td>2005 PU<sub>21</sub></td><td>40</td><td>6.46</td><td>283</td><td>0.06</td><td>23.75 ± 0.9</td><td>(3)</td><td>5.24 ± 0.14</td><td>-1.35 ± 0.08</td><td>Scat</td><td>Cliff</td></tr><tr><td>2005 QU<sub>182</sub></td><td>133</td><td>3.80 ± 0.32</td><td>416 ± 73</td><td>0.328<sup>+0.160</sup><sub>-0.09</sub></td><td>18.65 ± 0.9</td><td>(3)</td><td>3.66 ± 0.18</td><td>0.12 ± 0.11</td><td>Scat</td><td>Double-Dip</td></tr><tr><td>2005 RN<sub>43</sub></td><td>11</td><td>3.90 ± 0.05</td><td>679.0<sup>+55.0</sup><sub>-73.0</sub></td><td>0.107<sup>+0.029</sup><sub>-0.018</sub></td><td>20.34 ± 0.9</td><td>(3)</td><td>3.85 ± 0.16</td><td>-0.04 ± 0.08</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2005 TB<sub>190</sub></td><td>25</td><td>4.40 ± 0.11</td><td>464.0 ± 62.0</td><td>0.148<sup>+0.051</sup><sub>-0.036</sub></td><td>18.63 ± 1.89</td><td>(1)</td><td>4.42 ± 0.21</td><td>-0.29 ± 0.1</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2007 JF<sub>43</sub></td><td>29</td><td>5.42</td><td>388</td><td>0.08</td><td>40.89 ± 0.9</td><td>(3)</td><td>8.82 ± 0.16</td><td>0.74 ± 0.09</td><td>3:2 Res</td><td>Cliff</td></tr><tr><td>2007 OC<sub>10</sub></td><td>23</td><td>5.40 ± 0.1</td><td>309.0 ± 37.0</td><td>0.127<sup>+0.040</sup><sub>-0.028</sub></td><td>16 ± 0.9</td><td>(3)</td><td>5.31 ± 0.23</td><td>-0.25 ± 0.12</td><td>Detached</td><td>t-Double-Dip</td></tr><tr><td>2007 RW<sub>10</sub></td><td>50</td><td>6.40 ± 0.61</td><td>247.0 ± 30.0</td><td>0.083<sup>+0.038</sup><sub>-0.039</sub></td><td></td><td></td><td>3.68 ± 0.17</td><td>2.29 ± 0.12</td><td>Scat</td><td>Bowl</td></tr><tr><td>2007 TY<sub>430-A</sub></td><td>45</td><td>6.83</td><td>102</td><td>0.23</td><td>40.23 ± 0.37</td><td>(5)</td><td>6.71 ± 0.22</td><td>-0.83 ± 0.11</td><td>3:2 Res</td><td>Cliff</td></tr><tr><td>2007 TY<sub>430-B</sub></td><td>45</td><td>6.83</td><td>97</td><td>0.23</td><td>40.23 ± 0.37</td><td>(5)</td><td>7.06 ± 0.22</td><td>-0.61 ± 0.13</td><td>3:2 Res</td><td>Cliff</td></tr><tr><td>2007 UK<sub>126</sub></td><td>2</td><td>3.70 ± 0.1</td><td>599.0 ± 77.0</td><td>0.167<sup>+0.058</sup><sub>-0.038</sub></td><td>20.85 ± 3.17</td><td>(1)</td><td>4.21 ± 0.16</td><td>-0.41 ± 0.09</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2008 NW<sub>4</sub></td><td>36</td><td>5.71</td><td>297</td><td>0.1</td><td>22.89 ± 0.9</td><td>(3)</td><td>5.14 ± 0.21</td><td>-0.49 ± 0.11</td><td>HC</td><td>Double-Dip</td></tr><tr><td>2010 EK<sub>139</sub></td><td>5</td><td>3.80 ± 0.1</td><td>433.0<sup>+63.0</sup><sub>-64.0</sub></td><td>0.297<sup>+0.113</sup><sub>-0.078</sub></td><td></td><td></td><td>4.34 ± 0.16</td><td>-0.19 ± 0.08</td><td>7:2 Res</td><td>Double-Dip</td></tr><tr><td>2010 ER<sub>65</sub></td><td>46</td><td>5.22</td><td>341</td><td>0.12</td><td></td><td></td><td>5.85 ± 0.24</td><td>0.4 ± 0.13</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2010 ET<sub>65</sub></td><td>44</td><td>5.24</td><td>338</td><td>0.12</td><td></td><td></td><td>4.07 ± 0.17</td><td>-0.59 ± 0.09</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2010 KR<sub>59</sub></td><td>17</td><td>7.70 ± 0.3</td><td>110.06 ± 30.82</td><td>0.121 ± 0.037</td><td>23.89 ± 4.47</td><td>(6)</td><td>6.43 ± 0.33</td><td>3.58 ± 0.27</td><td>Centaur</td><td></td></tr><tr><td>2010 VW<sub>11</sub></td><td>31</td><td>5.46</td><td>304</td><td>0.13</td><td></td><td></td><td>3.88 ± 0.19</td><td>-0.33 ± 0.12</td><td>Detached</td><td>Double-Dip</td></tr><tr><td>2010 VZ<sub>98</sub></td><td>15</td><td>5.06</td><td>367</td><td>0.12</td><td>30.59 ± 1.12</td><td>(7)</td><td>8.99 ± 0.14</td><td>1.57 ± 0.09</td><td>Scat</td><td>Cliff</td></tr><tr><td>2012 DR<sub>30</sub></td><td>54</td><td>7.00 ± 0.35</td><td>188.0 ± 9.4</td><td>0.076<sup>+0.061</sup><sub>-0.025</sub></td><td>14.5 ± 1.1</td><td>(8)</td><td>5.39 ± 0.15</td><td>2.13 ± 0.09</td><td>HiHq</td><td>Bowl</td></tr><tr><td>2013 LU<sub>28</sub></td><td>1</td><td>8.34</td><td>118</td><td>0.06</td><td>15.06 ± 1</td><td>(9)</td><td>5.04 ± 0.16</td><td>1.66 ± 0.09</td><td>Scat</td><td>Bowl</td></tr><tr><td>2014 LV<sub>28</sub></td><td>42</td><td>5.71</td><td>268</td><td>0.13</td><td>18.54 ± 0.9</td><td>(3)</td><td>4.94 ± 0.18</td><td>0.09 ± 0.11</td><td>Scat</td><td>Double-Dip</td></tr><tr><td>2014 YF<sub>50</sub></td><td>30</td><td>5.39</td><td>315</td><td>0.12</td><td></td><td></td><td>5.66 ± 0.17</td><td>-0.48 ± 0.17</td><td>13:3 Res</td><td>Double-Dip</td></tr><tr><td>2015 SO<sub>20</sub></td><td>52</td><td>6.64</td><td>177</td><td>0.12</td><td>15.95 ± 0.9</td><td>(3)</td><td>4.5 ± 0.17</td><td>1.55 ± 0.1</td><td>Scat</td><td>Bowl</td></tr></tbody></table>

The different columns include absolute magnitude (Hv) and geometric albedo (p,.) in the visible, colour of the surface in the visible (S') and in the IR (SIR, and SIR$_{J}$), and dynamical class (Dyn. Class). References for visible colors: (1) ref. 10; (2) ref. 103; (3) Pinilla-Alonso personal communication; (4) ref. 57; (5) ref. 104; (6) ref. 105; (7) ref. 106; (8) ref. 35; (9) ref. 107; Lorenzi et al. 2023 ACM Abstract. Abbreviations in column Dynamical Class correspond to: CC, cold classical TNO; HC, hot classical TNO; Scat, scattering object; Res, resonant object; HiHq, high-inclination and high-perihelion object.
Extended Data Table 3 | Summary of spectral attributions

<table><thead><tr><th rowspan="2">Band position (μm)</th><th colspan="3">Band detection in each group</th><th colspan="4">Most probable Attributions</th><th rowspan="2">Tentative Attributions</th></tr><tr><th>Bowl</th><th>Double-dip</th><th>Cliff</th><th>H<sub>2</sub>O</th><th>CO<sub>2</sub> & CO</th><th>CH<sub>3</sub>OH</th><th>Complex organics</th></tr></thead><tbody><tr><td>1.5 & 1.65</td><td>f</td><td></td><td></td><td>O-H stretch</td><td></td><td></td><td></td><td></td></tr><tr><td>1.55</td><td></td><td>t</td><td>f</td><td>1<sup>st</sup> overtone<sup>62</sup></td><td></td><td>C-H, O-H 1<sup>st</sup> overtone<sup>62</sup></td><td>C-H, O-H, N-H 1<sup>st</sup> overtone<sup>62</sup></td><td></td></tr><tr><td>2.03</td><td>f</td><td></td><td></td><td></td><td></td><td></td><td>C≡N 2<sup>nd</sup> overtone</td><td></td></tr><tr><td>1.99 & 2.09</td><td></td><td>t</td><td>f</td><td></td><td></td><td>2.1 μm: O-H comb<sup>73</sup></td><td>C-H, O-H, N-H comb<sup>62</sup></td><td></td></tr><tr><td>2.3</td><td></td><td>t</td><td>f</td><td></td><td></td><td></td><td>comb with C≡N<sup>79</sup>, C=O 2<sup>nd</sup> overtone<sup>62</sup></td><td></td></tr><tr><td>2.5</td><td></td><td>t</td><td>f</td><td></td><td></td><td>2.27 μm asym comb<sup>73</sup></td><td>C-H<sup>62</sup>, N-H<sup>41</sup> comb,</td><td></td></tr><tr><td>2.7</td><td></td><td>f</td><td></td><td></td><td></td><td>2.34 μm sym comb<sup>73</sup></td><td>C≡N 1<sup>st</sup> overtone<sup>77,82</sup></td><td></td></tr><tr><td>2.77</td><td></td><td>f</td><td></td><td></td><td></td><td>C-H comb<sup>62</sup></td><td>C-H comb<sup>80</sup></td><td></td></tr><tr><td>2.9 - 3.3</td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>2.9 - 3.3</td><td></td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>2.9</td><td></td><td>t</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3.1</td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3.3 - 3.7</td><td></td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>3.9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4.26</td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td><td>H<sub>2</sub>S: S-H stretch<sup>91</sup></td></tr><tr><td>4.38</td><td></td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4.5</td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4.5</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4.62</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td>OCN<sup>-</sup>: C≡N stretch<sup>22</sup></td></tr><tr><td>4.68</td><td></td><td>f</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>4.9</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>t</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>t</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td>t</td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

Each attribution is marked as 'f' or 't' mark, respectively, meaning firm or tentative detections of an absorption band across the 3 groups. 'stretch' stands for stretching mode. 'comb' stands for combination mode. ('a)sym' stand for (a)symmetric).