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Paper: The Ongoing Decline in Activity of Comet 103P/Hartley 2
Authors: Ariel Graykowski, Guillaume Langin, David Chiron, Bruno Guillet, Franck Marchis, Nicolas Biver, Gérard Arlic, Bernard Baudouin, Etienne Bertrand, Randall Blake, Cyrille Bosquet, John K. Bradley, Isabelle Brocard, Christophe Cac, Alain Cagna, Nicolas Castel, Eric Chariot, Olivier Clerget, Tom Coarrase, Lucas Cogniaux, Julien Collot, Christophe Coté, Michel Deconinck, Jean-Paul Desgrees, Josselin Desmars, Giuseppe Di Tommaso, José Donas, William Drapeaud, Todd Forrester, Florent Fremont, Keiichi Fukui, Paul Garde, Jérôme Gaudilliere, Pascal Gaudin, Alexis Giacomoni, David Gineste, Patrice Girard, Jean Claude Gomez, Chuck Goodman, Gerard-Philippe Grandjean, Philippe Guiglion, David Havell, Patrick Huth, Kachi Iwai, Marc-Etienne Julien, Rachel Knight, Ryuichi Kukita, Petri Kuossari, Jean-Michel Ladruze, Anis Ben Lassoued, Cédric Latgé, Jean-Marie Laugier, Matthieu Lauvernier, Patrice Le Guen, Jean-Charles Le Tarnec, Didier Lefoulon, Liouba Leroux, Niniane Leroux, Arnaud Leroy, Chelsey Logan, Yohann Lorand, Elisabeth Maris, Jean-Pierre Masini, Nicola Meneghelli, Laurent Millart, Eric Miny, Mike Mitchell, Baptiste Montoya, Fabrice Mortecrette, Anouchka Nardi, Antoine Ngo, Denis Nicolas, Raphael Nicollerat, Takaya Okada, Wataru Ono, George Patatoukas, Jacqueline Payet-Ayrault, Patrick Picard, Claude Porchel, Kanai Potts, Michel Quienen, Martial Relier, Fabien Richardot, Darren Rivett, Matthew Ryno, Fadi Saibi, Sophie Saibi, Christian Sartini, Hiromichi Sasaki, Philippe Seibert, Masao Shimizu, Lucas Sifoni, Georges Simard, Petri Tikkanen, Ian Transom, Bernard Tregon, Frank Tyrlik, Laurent Vadrot, Michel Veuillet, Christian Voirol, Stefan Will, Corine Yahia, Phil Yehle, Neil Yoblonsky, Wai-Chun Yue
Figure caption: The observed decline in minimum reduced magnitude of Comet 103P/Hartley 2 across multiple apparitions. Previous apparitions include only COBS data; the 2023 apparition includes data from this work as well. The decreasing trend in brightness is indicative of progressive volatile depletion rather than changes in orbital geometry. If this trend continues, at the earliest, Hartley 2 will reach nuclear magnitude in year ∼2112, after ∼13 more active apparitions.
Paper: The Ongoing Decline in Activity of Comet 103P/Hartley 2
Authors: Ariel Graykowski, Guillaume Langin, David Chiron, Bruno Guillet, Franck Marchis, Nicolas Biver, Gérard Arlic, Bernard Baudouin, Etienne Bertrand, Randall Blake, Cyrille Bosquet, John K. Bradley, Isabelle Brocard, Christophe Cac, Alain Cagna, Nicolas Castel, Eric Chariot, Olivier Clerget, Tom Coarrase, Lucas Cogniaux, Julien Collot, Christophe Coté, Michel Deconinck, Jean-Paul Desgrees, Josselin Desmars, Giuseppe Di Tommaso, José Donas, William Drapeaud, Todd Forrester, Florent Fremont, Keiichi Fukui, Paul Garde, Jérôme Gaudilliere, Pascal Gaudin, Alexis Giacomoni, David Gineste, Patrice Girard, Jean Claude Gomez, Chuck Goodman, Gerard-Philippe Grandjean, Philippe Guiglion, David Havell, Patrick Huth, Kachi Iwai, Marc-Etienne Julien, Rachel Knight, Ryuichi Kukita, Petri Kuossari, Jean-Michel Ladruze, Anis Ben Lassoued, Cédric Latgé, Jean-Marie Laugier, Matthieu Lauvernier, Patrice Le Guen, Jean-Charles Le Tarnec, Didier Lefoulon, Liouba Leroux, Niniane Leroux, Arnaud Leroy, Chelsey Logan, Yohann Lorand, Elisabeth Maris, Jean-Pierre Masini, Nicola Meneghelli, Laurent Millart, Eric Miny, Mike Mitchell, Baptiste Montoya, Fabrice Mortecrette, Anouchka Nardi, Antoine Ngo, Denis Nicolas, Raphael Nicollerat, Takaya Okada, Wataru Ono, George Patatoukas, Jacqueline Payet-Ayrault, Patrick Picard, Claude Porchel, Kanai Potts, Michel Quienen, Martial Relier, Fabien Richardot, Darren Rivett, Matthew Ryno, Fadi Saibi, Sophie Saibi, Christian Sartini, Hiromichi Sasaki, Philippe Seibert, Masao Shimizu, Lucas Sifoni, Georges Simard, Petri Tikkanen, Ian Transom, Bernard Tregon, Frank Tyrlik, Laurent Vadrot, Michel Veuillet, Christian Voirol, Stefan Will, Corine Yahia, Phil Yehle, Neil Yoblonsky, Wai-Chun Yue
Figure caption: Panel (A) shows a 20 minute stack showing the diffuse coma of Hartley 2 in a crowded star field during its 2023 apparition. Observation taken with a Unistellar eVscope. Panel (B) shows the surface-brightness profile of the comet in blue, and the point at which the profile blends into the background of the image is represented by the dashed purple line.
Paper: The Ongoing Decline in Activity of Comet 103P/Hartley 2
Authors: Ariel Graykowski, Guillaume Langin, David Chiron, Bruno Guillet, Franck Marchis, Nicolas Biver, Gérard Arlic, Bernard Baudouin, Etienne Bertrand, Randall Blake, Cyrille Bosquet, John K. Bradley, Isabelle Brocard, Christophe Cac, Alain Cagna, Nicolas Castel, Eric Chariot, Olivier Clerget, Tom Coarrase, Lucas Cogniaux, Julien Collot, Christophe Coté, Michel Deconinck, Jean-Paul Desgrees, Josselin Desmars, Giuseppe Di Tommaso, José Donas, William Drapeaud, Todd Forrester, Florent Fremont, Keiichi Fukui, Paul Garde, Jérôme Gaudilliere, Pascal Gaudin, Alexis Giacomoni, David Gineste, Patrice Girard, Jean Claude Gomez, Chuck Goodman, Gerard-Philippe Grandjean, Philippe Guiglion, David Havell, Patrick Huth, Kachi Iwai, Marc-Etienne Julien, Rachel Knight, Ryuichi Kukita, Petri Kuossari, Jean-Michel Ladruze, Anis Ben Lassoued, Cédric Latgé, Jean-Marie Laugier, Matthieu Lauvernier, Patrice Le Guen, Jean-Charles Le Tarnec, Didier Lefoulon, Liouba Leroux, Niniane Leroux, Arnaud Leroy, Chelsey Logan, Yohann Lorand, Elisabeth Maris, Jean-Pierre Masini, Nicola Meneghelli, Laurent Millart, Eric Miny, Mike Mitchell, Baptiste Montoya, Fabrice Mortecrette, Anouchka Nardi, Antoine Ngo, Denis Nicolas, Raphael Nicollerat, Takaya Okada, Wataru Ono, George Patatoukas, Jacqueline Payet-Ayrault, Patrick Picard, Claude Porchel, Kanai Potts, Michel Quienen, Martial Relier, Fabien Richardot, Darren Rivett, Matthew Ryno, Fadi Saibi, Sophie Saibi, Christian Sartini, Hiromichi Sasaki, Philippe Seibert, Masao Shimizu, Lucas Sifoni, Georges Simard, Petri Tikkanen, Ian Transom, Bernard Tregon, Frank Tyrlik, Laurent Vadrot, Michel Veuillet, Christian Voirol, Stefan Will, Corine Yahia, Phil Yehle, Neil Yoblonsky, Wai-Chun Yue
Figure caption: Lightcurve of Comet 103P/Hartley 2. The lightcurve is fitted to the upper envelope of Unistellar (blue) and AFA (red) data points. COBS submitted data are displayed in gray. The upper envelopes of both sets of data points are in good agreement.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Radially variable dimensionless background state properties used in the dynamo simulation. Top left: temperature ﹩\widetilde{T}﹩ (red) and density ﹩\tilde{\rho }﹩ (blue); top middle: gravity ﹩\tilde{g}﹩ (black), entropic expansivity ﹩{\tilde{\alpha }}_{s}﹩ (red), and Grüneisen parameter ﹩\tilde{\gamma }﹩ (blue); top right: composition ﹩10\times \tilde{\xi }﹩ (black) and composition gradient ﹩d\tilde{\xi }/dr﹩, with inset showing details near the outer boundary; bottom left: effective entropy gradient ﹩{\left(d\tilde{s}/dr\right)}_{{\rm{eff}}}﹩ (black), where ﹩{\left(d\tilde{s}/dr\right)}_{{\rm{eff}}}=0﹩ is shown with a red dashed line, and the inset shows details of convective driving (see text); bottom middle: ﹩\Pr (\nu /\tilde{\kappa })﹩, which is a radially variable Prandtl number, or a dimensionless thermal conductivity, where the viscosity is ν is constant; bottom right: ﹩\mathrm{Pm}(\nu /\tilde{\lambda })﹩, which is a radially variable magnetic Prandtl number, or a dimensionless electrical conductivity.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Thermocompositional properties. Lines show properties for the preferred background model. Dagger symbols: calculated from the M. French et al. (2012) EOS. Blue lines and triangles: thermal stability density ratio (Equation (33)). Red lines and circles: compositional stability density ratio (Equation (34)). Green lines and squares: Γ (Equation (37)). Shading indicates the radial extent of thermocompositional layers. Blue shading: subadiabatic (radiative) thermally stratified stable layer. Red shading: superadiabatic compositionally stratified stable layer. Yellow shading: adiabatic (convective) layers. Thick black dashed lines: density ratio (Equation (26)), which is undefined in adiabatic (ds/dr = dξ/dr = 0) layers.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Properties of the nonadiabatic thermocompositional Jupiter interior model fitted to the EOS model of B. Militzer et al. (2022; double dagger), and comparisons with M. French et al. (2012; dagger) and B. Militzer et al. (2022). Top left: temperature T, density ρ, and gravity g (right vertical axis); top right: Grüneisen parameter γ and αscp,; bottom left: density profiles expanded to outer half, inset, near outer boundary (r = ro = 1, P = 1 bar); bottom right: composition ξ compared, specific entropy s, and density ratio Rρ = Γ.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Even gravitational harmonics Jn for the preferred interior model (black circles), compared to the harmonics computed for a linear density gradient model (red crosses), the Juno harmonics (D. Durante et al. 2020; blue circles and error bars), and the results of B. Militzer et al. (2022; green stars and dashed line in lower right corner). Top left: whereas ∣Jn∣ decreases strongly with n, ﹩| {J}_{n}| /{m}_{{\rm{rot}}}^{n/2}﹩ is relatively constant, allowing a visual comparison of all the even Jn on one plot (V. N. Zharkov & V. P. Trubitsyn 1978; B. Militzer & W. B. Hubbard 2023), where mrot is the small rotational parameter. Top right: on the outside plot the circle, green star, and blue error bars nearly overlap; inset axes show smaller scale.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Even zonal gravitational harmonics Jn for the preferred interior model (black squares), compared to the harmonics computed for a linear density gradient model (red crosses; see Appendix A), the Juno harmonics (D. Durante et al. 2020; two daggers, blue circles and error bars), and the results of B. Militzer et al. (2022; double dagger, green stars; green dashed line in the lower right corner shows the J10 value). Top left: whereas ∣Jn∣ decreases strongly with n, ﹩| {J}_{n}| /{m}_{{\rm{rot}}}^{n/2}﹩, where mrot is the small rotational parameter (V. N. Zharkov & V. P. Trubitsyn 1978), is relatively constant, allowing a visual comparison of all the harmonics on one plot (V. N. Zharkov & V. P. Trubitsyn 1978; B. Militzer & W. B. Hubbard 2023).
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Properties of the preferred Jupiter interior model, and comparisons with M. French et al. (2012; dagger) and B. Militzer et al. (2022; double dagger). (a) Temperature T, density ρ, and gravity g (right vertical axis). (b) Grüneisen parameter γ and αscp. (c) Density profiles expanded to outer half, inset, near outer boundary (r = ro = 1, P = 1 bar). (d) Composition ξ compared to Y + Z from B. Militzer et al. (2022), difference between specific entropy and its minimum value Δs = s − smin, buoyancy frequency N (see Section 2.3) is scaled on the right-hand-side vertical axis. This plot has an exponential (10r) horizontal axis to expand near r = 1.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Properties of the reference Jupiter interior model, and comparisons with M. French et al. (2012; dagger), B. Militzer et al. (2022; double dagger), and a polytrope with n = 1. Top left: temperature T, density ρ, and gravity g (right vertical axis); top right: Grüneisen parameter γ and αscp; bottom left: density profiles expanded to outer half, inset, near outer boundary (r = ro = 1, P = 1 bar); bottom right: composition ξ compared, specific entropy s, and density ratio Rρ = Γ.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Schematic of the preferred Jupiter interior model. Shading indicates the radial extent of thermocompositional layers. Blue shading: subadiabatic (radiative) thermally stratified stable layer. Red shading: superadiabatic compositionally stratified stable layer. Yellow shaded regions: adiabatic (convective) layers.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Results of dynamo simulation and comparison with observations. Images: magnetic field (purple-green) scaled by ﹩{\left({\rho }_{o}{\mu }_{0}{\lambda }_{i}{\rm{\Omega }}\right)}^{1/2}﹩, where ro = 0.994 is the outer-boundary radius and r = 1 corresponds to the mean radius of Jupiter (1-bar level). Fluid velocity (blue-red) in Reynolds number Re = v ro/ν units. Dashed lines on meridional images show transition radii between thermocompositional layers. (a) Magnetic energy spectra at r/ro = 1. Red triangles show spectrum at the time step corresponding to magnetic field images (panels (b)–(f)), gray lines, 76 spectra equally spaced over final ≃7% of the simulation, black line, time-average spectrum, blue circles, Lowes spectrum from Juno mission magnetic data (J. Connerney et al. 2022); (b, c, d) surfaces of the radial magnetic field Br and azimuthal field Bϕ in Mollweide projection; (e, f) azimuthal (ϕ) averages of Br and Bϕ, respectively; (g) zonal flow Rossby number ﹩\mathrm{Ro}={\langle {v}_{\phi }\rangle }_{\phi }/{\rm{\Omega }}{r}_{o}﹩ for cloud level of Jupiter (C. C. Porco et al. 2003), where Ro = ReEk, and the Ekman number Ek = 10−6, and for the simulation at three radii; (h–j) uϕ (in Re units) at three radii, in orthographic projection; (k, l) meridional slices of ur and uϕ.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: (a) Zonal flow vϕ(r, θ) and (b) density perturbation Δρ(r, θ) time-averaged over Δta = 307 rotations, ending with t = 5849 rotations; (c) zonal flow and (d) density perturbation time-averaged over Δtb = 347 rotations, ending with t = 7024 rotations. Dashed lines show the compositional transition radii at r = {0.8, 0.92, 0.975}.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Zonal gravity harmonic contributions resulting from the time-average Δta zonal flow. Filled symbols indicate positive values; open symbols indicate negative values. Contributions ΔJn for the full sphere, outer convective and thermally stable region, and dynamo region are compared to the wind model results of B. Militzer et al. (2022) and dynamo results of L. Kulowski et al. (2020). The observed harmonics Jn for Jupiter (D. Durante et al. 2020) and Saturn (L. Iess et al. 2019) have their odd n values (solid lines) displayed separately from their even n values (dashed lines).
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Fit of electrical conductivity (Equation (C1)) to the M. French et al. (2012) results (FEA12 in the legend). Electrical conductivity is scaled by the value σcore = 3.39 × 106 S m–1 at the core radius 0.0923RJ, where RJ = 6.9894 × 107 m is Jupiter’s mean radius.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: ΔJn for the two zonal flow time-average periods Δta (black) and Δtb (gray), compared to the models for Jupiter (Y. Kaspi et al. 2023) and Saturn (E. Galanti et al. 2025). The inset shows higher harmonics. See also Tables 1 and 2.
Paper: Thermocompositional Layers and Jupiter’s Gravity, Magnetic Field, and Supersolar Heavy Elements
Authors: Moritz Heimpel
Figure caption: Effect of hyperdiffusion used in the simulation (α = β = 3) on the Ekman number Ek = ν/ΩD2. The dashed vertical line shows lmax = 480.
Paper: Enceladus’s Tidal Heating: A Simple Approach
Authors: Yoram Lithwick
Figure caption: Orientation of the tidal bulge. Panel (a) displays the bulge of the ice shell under the action of the static tide, and the other panels display the bulge under the action of the total tide, depending on whether the shell is hard (panel (b)) or soft (panel (c)). For given values of γS and γice (angles of Saturn in its epicycle and of the shell, respectively), the resulting orientation of the bulge (γbul) depends on the shell’s hardness. When it is hard, the shell hardly changes its shape relative to γice. When it is soft, the bulge nearly points at Saturn, whatever the value of γice. The hardness parameter ﹩{ \mathcal R }﹩ is defined in Equation (27).
Paper: Enceladus’s Tidal Heating: A Simple Approach
Authors: Yoram Lithwick
Figure caption: Libration frequencies and amplitude of forced libration. Solid curves include libration of the core, and dotted curves neglect it. The dotted vertical line is at the resonant thickness of the shell.
Paper: Enceladus’s Tidal Heating: A Simple Approach
Authors: Yoram Lithwick
Figure caption: Three-layer model. The dotted circles represent the unperturbed (i.e., spherical) Enceladus.
Paper: Brownian Motion of Main-belt Asteroids on Human Timescales
Authors: Gary M. Bernstein
Figure caption: Each curve shows the forecast of the standard deviation of the azimuthal position of a middle MBA caused by discrete encounters over 10 yr with other MBAs that are smaller/fainter than the ﹩{H}_{{\rm{\min }}}﹩ value on the (lower) x-axis. The upper axis gives the ﹩{M}_{{\rm{\max }}}=M({H}_{{\rm{\min }}}).﹩ The left axis gives rms values in meters, the right the apparent shift in milliarcseconds for a heliocentric observer. The left and right panels differ in their assumptions about the scaling between the H value and mass for MBAs, as noted within each frame. Each line is for a different assumption about the rms uncertainty σM in the masses of individual asteroids gained from high-S/N observations of mutual encounters. Each star marks the dividing point between the N MBAs with M > σM and the smaller bodies with no useful measure of their mass (M < σM). The light dotted lines mark the level of azimuthal noise from deflections only by the bodies with M < σM. The black dashed curve is a conservative estimate of what can be achieved using LSST data to constrain MBA masses. Radial and vertical rms positions are factors of ≈7 and 45 lower than the azimuthal noise, respectively. This figure has been split into two panels for two different assumptions about mean MBA mass.
Paper: Brownian Motion of Main-belt Asteroids on Human Timescales
Authors: Gary M. Bernstein
Figure caption: Each panel shows statistics of the encounters between tracer MBAs from one region and deflector MBAs from another. As a function of the relative velocity at impact, the three curves show the mean squared value of the radial, azimuthal, and vertical components of the impulse direction ﹩\hat{{\boldsymbol{b}}}.﹩ The horizontal dashed line at value 1/3 would be the result for isotropic encounters, but we see that the azimuthal component of the impulse tends to be larger, with a variety of behaviors. The gray regions trace the distribution dN/dv of the rate of interactions per tracer per orbit per interval in v. These curves have a common (arbitrary) normalization, so the relative heights properly reflect the relative frequency of encounters among pairs of deflector and tracer regions.
Paper: Brownian Motion of Main-belt Asteroids on Human Timescales
Authors: Gary M. Bernstein
Figure caption: Differential counts of MBAs cataloged by the MPC are plotted vs. absolute magnitude H for the inner, middle, outer, and “other” regions of the main belt and for their total. We assume that they are complete for H ≤ 17 and extrapolate to fainter sources using the functional form from Equation (16), shown as the dotted curve. The inner and outer regions are slightly rescaled to help visual comparison of the curves’ shapes in the three MBA regions.
Paper: Exploring the Interior Structure and Mode of Tidal Heating in Enceladus
Authors: Amirhossein Bagheri, Mark Simons, Ryan S. Park, Alexander Berne, Douglas Hemingway, Mohit Melwani Daswani, Steven D. Vance
Figure caption:                         (a) Exploration of the correlation between the model parameters associated with Figure 7. The ranges of the plausible interior parameters are shown in Table 5. Black and yellow colors indicate the lowest and highest likelihoods. Units and plotting conventions are similar to Figure 18. (b) Model parameters for the case where at least 90% of the tidal heating is focused in the ice shell associated with Figures 7 and 21(a). The tidal heating in the shell is calculated using the formulation by M. Beuthe (2019) (Equation (B8)). Darkest and brightest colors indicate lowest and highest likelihoods. Units and plotting conventions are similar to Figure 18. (c) Model parameters for the case where at least 90% of the tidal heating is focused in the rocky core associated with Figures 7 and 21(a). The tidal heating in the core is calculated by subtracting the heat in the shell from the total tidal heating computed based on Equation (5). Units and plotting conventions are similar to Figure 18.
Paper: Exploring the Interior Structure and Mode of Tidal Heating in Enceladus
Authors: Amirhossein Bagheri, Mark Simons, Ryan S. Park, Alexander Berne, Douglas Hemingway, Mohit Melwani Daswani, Steven D. Vance
Figure caption: Top: k20 (left column) and k22 (right column) against mean ice shell thickness for models that assume an ice shell of constant thickness (dotted line), an ice shell with lateral variations in thickness (solid line), or a dissipative core (dotted and solid red lines). Bottom: similar to the top row except showing displacement Love numbers h20 and h22 plotted against mean ice shell thickness. x-axes are plotted on a log scale.
Paper: Detection of an NH3 Absorption Band at 2.2 μm on Europa
Authors: A. Emran
Figure caption: Upper panel: average reflectance spectrum with corresponding standard error bars across all wavelengths for the pixels within the detected clusters from NIMS observation 11ENCYCLOD01A (see Figure 4). The broad absorption features near ∼1.5 and ∼2.0 μm are characteristic of H2O ice (W. Grundy & B. Schmitt 1998; R. Mastrapa et al. 2008). A distinct absorption feature centered at ∼2.20 μm is indicative of NH3-bearing species (marked by the dashed blue vertical line). Note that the average reflectance of each cluster (four in total; see Figure 4) is given in Appendix Figure 10. Bottom panel: Gaussian band fit to the continuum-subtracted average spectrum shows a 2.20 ± 0.02 μm absorption feature with a band depth of 1.59% ± 0.16%.