# Influence of hydrothermal asteroidal conditions on the molecular structure and isotopic compositions of polycyclic aromatic hydrocarbons

Marceau Lecasble, Sylvain Bernard, Jean-Christophe Viennet, Isis Criouet, Laurent Remusat

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## To cite this version:

Marceau Lecasble, Sylvain Bernard, Jean-Christophe Viennet, Isis Criouet, Laurent Remusat. Influence of hydrothermal asteroidal conditions on the molecular structure and isotopic compositions of polycyclic aromatic hydrocarbons. Icarus, 2023, 401, pp.115603. 10.1016/j.icarus.2023.115603. hal-04104875

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Submitted on 24 May 2023

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# Influence of hydrothermal asteroidal conditions on the molecular structure and isotopic compositions of polycyclic aromatic hydrocarbons

Marceau Lecasble*, Sylvain Bernard, Jean-Christophe Viennet, Isis Criouet, Laurent Remusat

Muséum National d'Histoire Naturelle, Sorbonne Université, CNRS UMR 7590, IMPMC, Paris, France

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## ARTICLE INFO

Keywords:

Polycyclic aromatic hydrocarbons
Carbonaceous chondrites
Aqueous alteration
Laboratory experiments

## ABSTRACT

A variety of polycyclic aromatic hydrocarbons (PAHs) are reported in carbonaceous chondrites (CCs) and in the interstellar medium (ISM). Although PAHs in CCs are not as large as those detected in the ISM, their carbon isotope composition is interpreted as pinpointing an interstellar origin. In contrast, their hydrogen isotope composition can be related to the extent of secondary processes, as is the proportion of alkylated PAHs within CCs. Here, we experimentally investigate the molecular and isotopic evolution of PAHs under simulated asteroidal hydrothermal conditions at 150 °C. Results show that PAHs are chemically stable under these conditions whatever their size, i.e. no destruction, conjugation nor alkylation occurs, even in the presence of other reactive organic molecules. Plus, PAHs retain their carbon isotope compositions even in the presence of another carbon-rich reservoir, either organic or inorganic. On the other hand, their hydrogen isotope composition is modified through exchange with water. Of note, as shown by additional experiments, the presence of smectites, abundant in CCs, impacts the relative abundances of extractable PAHs, saponite trapping more efficiently the larger PAHs. Altogether, results of the present experiments show that PAHs of CCs can be used as tracers of both pre-accretion and secondary processes.

## 1. Introduction

Organic matter in chondrites is usually divided into an insoluble fraction (IOM - 50 to 90 wt%) and a soluble fraction (SOM - 10 to 50 wt %). While the IOM consists in a reticulated macromolecule made of aromatic units interconnected by short and branched aliphatic chains (Derenne and Robert, 2010; Vinogradoff et al., 2017), the SOM is a mixture of diverse soluble compounds such as carboxylic acids, amino acids, nucleobases (Pizzarello, 2006; Remusat, 2015; Martins et al., 2015) and polycyclic aromatic hydrocarbons (PAHs - Naraoka et al., 2000; Lecasble et al., 2022). PAHs are organic molecules consisting of two or more fused benzene rings (Richter and Howard, 2000; Abdel-Shafy and Mansour, 2016) and their size in CCs range from 2 rings (naphthalene – 10C atoms) to 7 rings (coronene – 24C atoms) (Slavi-cinska et al., 2022; Sabbah et al., 2017, 2022). The PAHs detected in CCs may originate from the interstellar medium (ISM), as previously sug-gested (Plows et al., 2003). In fact, PAHs are abundant and ubiquitous in the ISM, representing up to 20% of the total carbon (Leger and Puget, 1984; Allamandola et al., 1985, 1989; Tielens, 2008). These PAHs could have formed either via the irradiation of simple gas-phase molecules and

interstellar dust mantles by ultraviolet (UV) light or via reactions in circumstellar outflows of asymptotic giant branch (AGB) stars (Sagan and Khare, 1979; Cherchneff et al., 1992; Tielens and Charnley, 1997; Greenberg et al., 2000).

### 1.1. Degradation/polymerization of PAHs

Yet the presence, in CCs, of PAHs inherited from the ISM remains a subject of debate, in particular because sizes do not match. Chondritic PAHs have a maximum size of ~24C atoms (Sabbah et al., 2017, 2022) while interstellar PAH sizes range from 50 carbon atoms (Tielens, 2008, 2011) to thousands of carbon atoms (Allamandola et al., 1989; Pend-leton and Allamandola, 2002). This discrepancy could result from sec-ondary processes having modified all the constituents of CCs (Brearley, 2006; Cody et al., 2011; Le Guillou and Brearley, 2014; Vinogradoff et al., 2018; Viennet et al., 2022; Suttle et al., 2021). In fact, almost all the CCs have experienced aqueous alteration episodes, mostly triggered by the melting of ice due to the radioactive decay of short-lived radio-nucleides such as $^{26}$Al (McSween, 1979; Brearley, 2006; Krot et al., 2006; Verdier-Paoletti et al., 2017; Fujiya, 2018), but also possibly by

<footnote>* Corresponding author.
E-mail address: marceau.lecasble@mnhn.fr (M. Lecasble).</footnote>
impact heating, solar heating, or atmospheric ablation (Turner et al., 2021). Although it has been proposed that PAHs are inherited from the ISM (Yang and Epstein, 1983, 1984; Kerridge, 1983; Allamandola et al., 1987), Shock and Schulte (1990) predicted that, if exposed to hydrothermal conditions, PAHs would break down, leading to the production of carboxylic and amino acids. Experimental data on the stability of PAHs under hydrothermal conditions are thus required to provide new constraints on the origin of PAHs in CCs.

## 1.2. Alkylation of PAHs

The abundance of alkylated PAHs in CCs, i.e. PAHs with side chains containing up to 4 additional carbon atoms (Pering and Ponnamperuma, 1971; Hahn et al., 1988) constitute an interesting point to consider. It has been suggested that a chromatographic separation of alkylated and non-alkylated PAHs occurs during aqueous alteration on the parent body. As alkylated PAHs are less soluble than non-alkylated equivalents, this may explain the larger relative amount of alkylated PAHs with respect to non-alkylated equivalent in more altered CCs (Wing and Bada, 1991a, 1991b; Shiu and Ma, 2000; Elsila et al., 2005; Lecasble et al., 2022). However, no alkylated PAHs were detected in the Paris meteorate, a weakly altered CM (Martins et al., 2015), suggesting that alkylated PAHs could rather be produced during aqueous alteration events. Experimental data on the alkylation of PAHs under hydrothermal conditions are thus required to provide new constraints on the origin of alkylated PAHs and their proportion in CCs.

## 1.3. Carbon isotope evolution

The carbon isotope signature of PAHs has also been investigated. The PAHs in CCs exhibit carbon isotope compositions defining two negative trends (i.e. the pyrene and the fluoranthene series) with increasing PAH size (larger PAH have lower $\delta^{13}\text{C}$ values - Sephton et al., 1998; Gilmour and Pillinger, 1994; Naraoka et al., 2000; Huang et al., 2015; Lecasble et al., 2022). This has been interpreted as resulting from the production of these PAHs via cycle addition having occurred at very low temperature, i.e. before their accretion onto parent bodies (Gilmour and Pillinger, 1994; Naraoka et al., 2000). Since almost all the CCs have experienced aqueous alteration episodes, the preservation of these signatures implies that the carbon isotope composition of PAHs can withstand hydrothermal conditions. However, this has not been demonstrated experimentally, yet. Experimental data on the evolution of the carbon isotope compositions of PAHs under hydrothermal conditions in the presence of other carbon reservoirs are thus required.

## 1.4. Hydrogen isotope evolution

In contrast to the carbon isotope composition, the deuterium isotope composition of PAHs in CCs does not pinpoint an interstellar origin. In fact, the PAHs in the ISM are expected to be D-rich (Millar et al., 2000; Peeters et al., 2004; Salama, 2008), with D enrichment resulting from unimolecular photodissociation (Allamandola et al., 1987, 1989), gas phase ion-molecule reactions (Dalgarno and Lepp, 1984) or gas-grain reactions (Tielens and Charnley, 1997; Sandford, 2002). In contrast, the PAHs in CCs are D-poor compared to other organic compounds such as amino acids (Oba and Naraoka, 2003; Elsila et al., 2012; Huang et al., 2015; Lecasble et al., 2022; Graham et al., 2022). While these low contents in D have been interpreted by some authors as inherited from interstellar conditions (Huang et al., 2015; Graham et al., 2022), Lecasble et al. (2022) interpreted these values as the consequence of hydrogen isotope exchange with D-poor water during aqueous alteration episodes. Consistently, Alexander et al. (1982) showed that PAHs are sensitive to D-exchange in dry conditions, and Oba and Naraoka (2003) showed that such process can occur in acidic aqueous conditions. However, the parent bodies of CCs have experienced aqueous alteration under rather basic conditions (Zolotov, 2012; Takir et al., 2013; Suttle

et al., 2021, 2022). It thus remains to demonstrate that PAHs may experience D-exchange under such conditions.

A last point worth to investigate is the possible influence of clay minerals. CCs are rich in clay minerals (Pearson et al., 2006; Garvie and Buseck, 2007; Le Guillou and Brearley, 2014; Yesiltas and Kebukawa, 2016; Changela et al., 2018) and it has been shown that clay minerals may influence organic reactions (cyclization, dehydration, Michael-addition and IOM formation – Vinogradoff et al., 2020a, 2020b; Vien-net et al., 2022). Besides some rare studies having shown that the presence of montmorillonite could enhance PAH substitution and polymerization (Hagiwara et al., 2000; Watson and Sephton, 2015) and that serpentine does not produce new PAHs (Giese et al., 2019), no laboratory experiments have been conducted to investigate the effect of saponite (the most abundant clay mineral in CCs with serpentine - Brearley, 2006) on PAHs under hydrothermal conditions typical of asteroids.

Here, we report series of laboratory experiments specifically designed to investigate the molecular and isotopic evolution of PAHs under hydrothermal conditions simulating aqueous alteration events having occurred within/onto carbonaceous asteroids. Experiments were conducted under hydrothermal conditions at 150 °C with phenanthrene (3 rings – 178 amu), pyrene (4 rings – 202 amu), coronene (7 rings – 300 amu) and graphene, in the presence of other organic carbon reservoirs (hexane, glycine, acetic acid), in the presence of $^{13}\text{C}$-enriched compounds, either organic or inorganic (glycine, graphitic carbon and carbonates), in the presence of $\text{D}_2\text{O}$ and in the presence of pure saponite.

# 2. Materials and methods

## 2.1. Starting materials

Most of the starting materials were provided by Sigma Aldrich: Phenanthrene (>99.5%), pyrene (98%), coronene (97%), graphene nanoplatelet (powder), $\text{D}_2\text{O}$ (99.9 atom % D), carbon-$^{13}\text{C}$ (99 atom % $^{13}\text{C}$), calcium carbonate-$^{13}\text{C}$ (99 atom % $^{13}\text{C}$), glycine (> 99%), acetic acid (> 99.7%), and glycine-$^{13}\text{C}_2$ (99 atom % $^{13}\text{C}$). Hexane (>99%) was provided by Roth. The pure saponite used for the present experiments ($\text{Na}_{0.4}(\text{Si}_{3.6}\text{Al}_{0.4})\text{Mg}_3\text{O}_{10}(\text{OH})_2$) was synthesized from a gel produced by mixing an $\text{AlCl}_3$ solution, a $\text{Na}_2\text{SiO}_3$ solution and a $\text{MgCl}_2$ solution at 0.2 M, and exposed to 230 °C for 10 days. Saponite purity has been checked with XRD, FTIR and CHNS analysis. The mineral is pure and contains no carbon.

## 2.2. Experiments in reactors

Organic compounds (powdered) and minerals were loaded into 20 mL Parr© Ti-reactors under argon atmosphere (>99.999%; Air Liquide, ALPHAGAZ 1) with 10 mL degassed bi-distilled water (Table 1). Water was degassed using Ar with the same purity. Reactors were maintained for 28 days at 150 °C (4.7 bars saturation vapor pressure). Gas present at 150 °C in reactors at the end of the experiment were identified and quantified by gas chromatography coupled with thermal conductivity detection (GC-TCD). Then, reactors were cooled down at room temperature and opened. Reactors were rinsed with dichloromethane (DCM). Extracts were dried and weighed for quantification. In the case of the experiment with saponite, samples were filtrated (vacuum driven glass filtration unit, 47 mm GSWP filters with 0.22 µm pores – Merck Millipore), without sonication before drying. Non-polar organics like hydrocarbons were extracted and analysed by GC-FID for evaluation of PAH molecular evolution. Yields corresponds to ratio between starting and dried recovered organics.

## 2.3. Experiment in capsules

Some experiments were conducted in gold capsules due to the limited quantity of materials available (coronene, graphene, $^{13}\text{C}$ glycine,
<table><caption>**Table 1**
List of the experiments conducted in the present study.</caption><thead><tr><th>Experiments</th><th>Temperature</th><th>Duration</th><th>Container</th><th>Organics</th><th>Minerals</th><th>Water</th><th>Analysis</th><th>Yield</th></tr></thead><tbody><tr><td>Phenanthrene + Pyrene (P/P)</td><td>150 °C</td><td>28 days</td><td>reactors</td><td>100 mg</td><td></td><td>10 mL</td><td>GC-TCD, GC-FID</td><td>98.2%</td></tr><tr><td>Coronene</td><td>150 °C</td><td>3 months</td><td>capsules</td><td>2.5 mg</td><td></td><td>100 µL</td><td>GC-FID</td><td>-</td></tr><tr><td>Graphene</td><td>150 °C</td><td>3 months</td><td>capsules</td><td>2.5 mg</td><td></td><td>100 µL</td><td>GC-FID</td><td>-</td></tr><tr><td>P/P + hexane</td><td>150 °C</td><td>28 days</td><td>reactors</td><td>50 mg + 50 mg</td><td></td><td>10 mL</td><td>GC-FID</td><td>97.4%</td></tr><tr><td>P/P + glycine</td><td>150 °C</td><td>28 days</td><td>reactors</td><td>50 mg + 50 mg</td><td></td><td>10 mL</td><td>GC-FID</td><td>98.2%</td></tr><tr><td>P/P + acetic acid</td><td>150 °C</td><td>28 days</td><td>reactors</td><td>50 mg + 50 mg</td><td></td><td>10 mL</td><td>GC-FID</td><td>97.2%</td></tr><tr><td>P/P + glycine <sup>13</sup>C</td><td>150 °C</td><td>7 days</td><td>capsules</td><td>5 mg + 45 mg</td><td></td><td>100 µL</td><td>GC-FID, GC-irMS</td><td>96.3%</td></tr><tr><td>P/P + graphitic carbon <sup>13</sup>C</td><td>150 °C</td><td>7 days</td><td>capsules</td><td>5 mg</td><td>45 mg</td><td>100 µL</td><td>GC-FID, GC-irMS</td><td>94.2%</td></tr><tr><td>P/P + calcium carbonate <sup>13</sup>C</td><td>150 °C</td><td>7 days</td><td>capsules</td><td>5 mg</td><td>45 mg</td><td>100 µL</td><td>GC-FID, GC-irMS</td><td>93.9%</td></tr><tr><td>P/P + D<sub>2</sub>O</td><td>150 °C</td><td>7 days</td><td>capsules</td><td>5 mg</td><td></td><td>100 µL</td><td>GC-FID, GC-irMS</td><td>97.9%</td></tr><tr><td>P/P + saponite</td><td>150 °C</td><td>28 days</td><td>reactors</td><td>100 mg</td><td>900 mg</td><td>10 mL</td><td>GC-TCD, GC-FID</td><td>84.6%</td></tr></tbody></table>

<sup>13</sup>C graphitic carbon, <sup>13</sup>C calcium carbonate and D<sub>2</sub>O). Three cm-long gold capsules were prepared from a 5.4 mm-large x 0.2 mm-thickness tube (Heraeus Deutschland GmbH & Co. KG). After introduction of the samples, water was added with a glass syringe in a glove box under argon atmosphere (> 99.999% - Air Liquide ALPHAGAZ 1). Then, capsules were welded and put into 20 mL Parr© reactors in Ti filled with 5 mL of bi-distilled water and placed in an oven for 7 days or 3 months at 150 °C. Water was added to the reactors to prevent explosion of the capsules by maintaining a saturation vapor pressure of ~4.7 bar. At the end of the experiments, capsules were cleaned, opened and immersed in 5 mL of DCM. In the presence of minerals, samples were centrifuged. Organics were then analysed by GC-FID (Gas Chromatography-Flame Ionization Detector) to quantify phenanthrene and pyrene content and to check for potential molecular evolution. For isotope exchange, experiments were also performed following this setup.

## 2.4. Gas Chromatograph – thermal conductivity detector (GC-TCD)

We used a Shimadzu GC-2014 equipped with a thermal conductivity detector (TCD-2014) operated at IMPMC, MNHN (Paris, France) for gas identification and quantification. After connection of the reactor, a < 0.01 bar vacuum was set in the sampling line using a DIVAC 1.4HV3C primary vacuum oil-free pump. Then, samples were injected in the GC through this sampling line. Ultra-high-quality argon (> 99.999% - Air Liquide ALPHAGAZ 1) was used as carrier gas. Two columns, HayeSep Q (80/100 mesh, 1.8 m × 1/8 in., 2 mm) followed by a Molecular Sieve 13× (60/80 mesh, 1.8 m × 1/8 in., 2 mm), were combined for optimal gas separation. The reactor and the injection line were kept at 150 °C. After connection of the reactors but before their openings, blanks chromatograms were collected to rule out leaks on the line (named control run hereafter). During analysis, the GC oven temperature was kept at 60 °C during 3 min and then increased at 20 °C/min until 110 °C was reached then held 6 min. Gas mixtures provided by Air Products were used for calibration of partial pressures in the gas volume sent into the GC.

## 2.5. Gas Chromatography-flame ionization detector analysis (GC-FID)

Phenanthrene and pyrene were analysed and quantified using an Agilent Technologies 7890B GC equipped with a flame ionization detector (FID) operated at IMPMC, MNHN (Paris, France). The GC was equipped with a HP-5 (30 m × 0.32 mm, 0.25 µm film) capillary column coated with (5%-Phenyl)-methylpolysiloxane. Ultra-high-purity helium was used as carrier gas. The samples were injected in split mode with a ratio of 2 and the injector temperature was set at 280 °C. The oven temperature was kept at 75 °C during 0.5 min and then increased at 20 °C/min until 250 °C was reached and held for 1 min. For coronene and graphene experiments, temperature was kept at 150 °C during 0.5 min and then increased at 30 °C/min until 300 °C was reached and held 5 min.

## 2.6. Gas Chromatography-isotope ratio mass spectrometry analysis (GC-irMS)

Compound-specific carbon and hydrogen isotope analyses were performed on an Elementar VisION isotopic mass spectrometer interfaced with an Agilent Technologies 7890 B GC through a GC5 Furnace system, installed at IMPMC, MNHN (Paris, France). Ultra-high purity helium was used as carrier gas. The oven was fitted with a HP-5 fused silica column (30 m × 0.32 mm, 0.25 µm film). For carbon analysis, 0.2 µL of each extract were injected at 280 °C in split mode with a ratio of 2. For hydrogen analysis, the injection volume was 5 µL. In both cases, the oven temperature was kept at 170 °C during 1 min and then increased at 20 °C/min until 280 °C was reached and held for 4 min. After the 4 min solvent delay, the products were directed through a 350 °C transfer line to the Elementar GC5 Furnace. For carbon-isotope analysis, organic molecules were oxidized in CO<sub>2</sub> thanks to a quartz tube packed with CuO/Pt wire set at 850 °C in. For hydrogen-isotope analysis, the GC5 was equipped with a ceramic tube operated at a temperature of 1250 °C, converting compounds into H<sub>2</sub>. Detector was operated at room temperature. The maximum uncertainties (on session standards or on samples) and the number of analysis are given. Results were corrected using international reference material: naphthalene (δ<sup>13</sup>C<sub>PDB</sub> = −26.12 ± 0.02 ‰, δD<sub>VSMOW</sub> = −58.6 ± 1.0 ‰) and phenanthrene (δ<sup>13</sup>C<sub>PDB</sub> = −25.39 ± 0.03 ‰, δD<sub>VSMOW</sub> = −84.1 ± 1.3 ‰) (Indiana University in Bloomington, USA – Schimmelmann et al., 1999). A session drift correction has been applied using in-house phenanthrene and pyrene standards and for hydrogen measurement, a H<sub>2</sub> correction was calculated and applied (Sessions et al., 2001). In the following, hydrogen isotopic ratios are expressed as isotope abundance (D/(D + H)), while carbon isotopic ratios are expressed in the δ notation relative to the international Pee Dee Belemnite standard following the equation:

$$ \delta^{13}\text{C}_{\text{PDB}}^{\text{‰}} = \left[ \left( \frac{^{13}\text{C}/^{12}\text{C}}{\text{sample}} \right) \div \left( \frac{^{13}\text{C}/^{12}\text{C}}{\text{PDB}} \right) - 1 \right]^{\text{a}} \times 10^{3}. $$

# 3. Results

## 3.1. Experiments with phenanthrene and pyrene

We conducted experiments with phenanthrene and pyrene at 150 °C for 28 days (Table 1). At the end of the experiments, no C-containing permanent gas was detected in the gas phase as revealed by GC-TCD (Fig. 1). The solvent extract of the residues of the experiments contain both pyrene and phenanthrene as revealed by GC-FID (Fig. 2), in relative amounts similar to those of the starting materials (98.2% of the initial pyrene and phenanthrene compounds were recovered at the end of the experiments). The missing PAHs were likely lost during the extraction procedure and sample handling.

## 3.2. Experiments with coronene and graphene

Similar experiments in simulated asteroidal conditions have been
<figure><img src="image_4.png" /><figcaption>**Fig. 1.** GC-TCD chromatograms of the gas phase of the experiments conducted in reactors (28 days). Also shown are the chromatograms of the air and control runs conducted before the openings of the reactors. V1 and V2 are peaks corresponding to valve rotations. Vertical scales are equal.</figcaption></figure>

conducted with coronene and graphene at 150 °C for 3 months (Table 1). The solvent soluble products of the experiments conducted with coronene only contain coronene and benzo[ghi]perylene, a minor contaminant already detected in the starting materials (Fig. 2). The quantification is complicated as coronene compounds do not elute properly. There is no solvent soluble compound detected in the experiments conducted with graphene, nor in the starting materials since graphene is not soluble at all and free of contaminant (Fig. 2).

### 3.3. Experiments with reactive and small molecules

Experiments with phenanthrene and pyrene have also been conducted at 150 °C for 28 days in the presence of reactive organic compounds, namely hexane, glycine and acetic acid (Table 1). The solvent soluble extracts of the experimental products contain both pyrene and phenanthrene as revealed by GC-FID (Fig. 2), in relative amounts similar to those of the starting materials (97.6% of the initial pyrene and phenanthrene compounds were recovered at the end of the experiments). The starting reactive organic compounds are not detected. Hexane may be diluted in the DCM peak and both glycine and acetic acid are either not extracted with DCM or not eluted with our non-polar HP-5 GC column. No new hydrocarbons are detected.

### 3.4. Experiments with ¹³C-enriched materials

Experiments with phenanthrene and pyrene have also been conducted at 150 °C for 7 days in the presence of ¹³C-enriched organic or inorganic compounds, namely glycine, graphitic carbon and calcium carbonate (Table 1). The solvent extract of the experimental residues contains both pyrene and phenanthrene as revealed by GC-FID (Fig. 2), in relative amounts similar to those of the starting materials (94.8% of the initial pyrene and phenanthrene compounds were recovered at the end of the experiments). Most important, the δ¹³C~PDB~ values of the recovered pyrene and phenanthrene compounds were identical (within error bars) to those of the starting materials (Table 2 – Fig. 3).

### 3.5. Experiment with perdeuterated water

Experiments with phenanthrene and pyrene have also been conducted at 150 °C for 7 days in the presence of pure D₂O (Table 1). The solvent extract of the residues of these experiments contain both pyrene and phenanthrene as revealed by GC-FID (Fig. 2), in relative amounts similar to those of the starting materials (97.9% of the initial pyrene and phenanthrene compounds were recovered at the end of the

experiments). Interestingly, the D abundance of the recovered pyrene and phenanthrene compounds are significantly higher than those of the starting materials (Table 3).

### 3.6. Experiments with saponite

We also conducted experiments with phenanthrene and pyrene at 150 °C for 28 days in the presence of saponite (Table 1). At the end of the experiment, 0.02 bar of CO₂ was detected in the gas phase as revealed by GC-TCD (Fig. 1). The solvent extract of the residues of the experiments contain both pyrene and phenanthrene as revealed by GC-FID (Fig. 2), in relative amounts different from those of the starting materials: only 91.4 and 77.8% of the initial phenanthrene and pyrene compounds, respectively, were recovered in solvents at the end of the experiments (Fig. 4). Of note, the solid residues of the experiments contain about 1.4 wt% of organic carbon, which correspond to about 80% of the missing carbon (12.28 mg vs 15.40 mg) in the soluble fraction. As a fraction of saponite (3.2%) has been lost (871.2 mg of residual saponite instead of 900 mg initially), either due to dissolution or during the extraction process and sampling process, this may explain in part the missing C (Fig. 4).

## 4. Discussion

### 4.1. Influence of hydrothermal conditions on the molecular structure of PAHs

The presence, in CCs, of PAHs inherited from the ISM remains a subject of debate, in particular because sizes do not match: the PAHs in CCs have a lower molecular weight than their interstellar counterparts. To explain this discrepancy, some authors have invoked the effect of aqueous alteration which may break down large PAHs leading to the production of smaller ones and other molecules such as carboxylic and amino acids (Shock and Schulte, 1990). However, neither the degradation of the PAHs nor the production of other hydrocarbons occurred in the present experiments, whatever the size of the PAHs used as starting materials (including graphene which can be seen as a model for ISM-like PAHs). Moreover, we show that phenanthrene, pyrene and coronene can withstand hydrothermal asteroidal conditions (i.e. 150 °C). As shown by the experiments conducted with graphene, high molecular weight PAHs like those detected in the ISM likely withstand asteroidal conditions as well, especially as they are more refractory than lower molecular weight PAHs (Pendleton and Allamandola, 2002). The diversity in low molecular weight PAHs in CCs is thus likely not a consequence of the alteration conditions experienced by asteroids. These PAHs have rather been
<figure><img src="image_5.png" /><figcaption>**Fig. 2.** GC-FID chromatograms of solvent extracts after a) experiment with phenanthrene and pyrene, coronene and graphene, b) experiments with other materials and c) experiments with saponite. No molecular evolution is observed in our experimental conditions.</figcaption></figure>
<caption>**Table 2**</caption>

Carbon isotope composition in δ¹³CₚD₃ ‰ for phenanthrene and pyrene after experiments at 150 °C during 7 days with glycine-¹³C₂, carbon-¹³C and calcium carbonate-¹³C. Uncertainties correspond to standard deviations on session standards. (x):number of replicates.

<table><thead><tr><th></th><th>Starting P/P<br>δ¹³CₚD₃ ‰</th><th>P/P + glycine-¹³C₂<br>δ¹³CₚD₃ ‰</th><th>P/P + carbon-¹³C<br>δ¹³CₚD₃ ‰</th><th>P/P + calcium carbonate-¹³C<br>δ¹³CₚD₃ ‰</th></tr></thead><tbody><tr><td>Phenanthrene</td><td>-25.35 ±<br>0.17 (24)</td><td>-25.55 ±<br>0.25 (4)</td><td>-25.46 ±<br>0.17 (6)</td><td>-25.49 ± 0.17<br>(6)</td></tr><tr><td>Pyrene</td><td>-25.03 ±<br>0.09 (24)</td><td>-24.89 ±<br>0.08 (4)</td><td>-24.96 ±<br>0.09 (6)</td><td>-24.98 ± 0.09<br>(6)</td></tr></tbody></table>

accreted as is, implying that they are likely present in the ISM or in the protosolar nebula.

No PAHs larger than coronene have been found in CCs with laser desorption mass spectrometry, a more suitable method for large PAHs compared to soluble extraction and gas chromatography (Sabbah et al., 2017, 2022), even though they are detected in the ISM. Thus, either large PAHs have somehow been destroyed or have simply not been accreted onto asteroids. Oxidative photochemistry in the protosolar disk could have been responsible for the destruction of PAHs (Lee et al., 2010; Anderson et al., 2017), the fast accretion of low molecular weight PAHs having preserved them from destruction. In fact, it has been suggested that their accretion could have been faster than their destruction, compared to what have occurred for larger PAHs (Derenne et al., 2005). In contrast to large PAHs, small PAHs could have thus been condensed on ice or silicate grains and then accreted to form parent bodies and stored in solids (Derenne et al., 2005; Michoulier et al., 2018).

The relative abundance of alkylated versus non alkylated PAHs has been shown to be correlated to the extent of aqueous alteration (Elsila et al., 2005; Lecasble et al., 2022). Rather than a production of alkylated PAHs from non-alkylated PAHs during aqueous alteration, it has been suggested that non-alkylated PAHs are preferentially lost during fluid circulation as a result of a selective chromatographic separation, non-alkylated PAHs being more water soluble than their alkylated counterparts (Hahn et al., 1988; Wing and Bada, 1991a, 1991b; Elsila et al., 2005). Strengthening this hypothesis, the laboratory experiments conducted in the present study showed that alkylation of PAHs does not occur under asteroidal conditions (i.e. 150 °C), even in the presence of reactive and small organic molecules. However, if both alkylated and non-alkylated PAHs were accreted onto asteroids, alkylated PAHs should be detected in all the CCs. But this is apparently not the case in the Paris meteorite (Martins et al., 2015), even though it has experienced weaker alteration compared to other CMs. Plus, if non-alkylated

PAHs are lost via chromatographic separation, the total abundance of PAHs should be correlated with the degree of alteration for series of CCs originating from the same parent body. But this is apparently not the case neither (Pering and Ponnamperuma, 1971; Martins et al., 2015; Lecasble et al., 2022). An explanation for this paradox may reside in the brecciated nature of most CCs (Lentfort et al., 2021), each fragment having potentially experienced an individual history.

## 4.2. Influence of hydrothermal conditions on the isotope composition of PAHs

The production of PAHs in the ISM involves carbon addition and cyclization processes (Tielens and Charnley, 1997), leading to C-isotope

<caption>**Table 3**</caption>

Deuterium abundance as D/(D + H) for phenanthrene and pyrene after experiments at 150 °C during 7 days with D₂O. Uncertainties correspond to standard deviations on session standards and on samples. (x): number of replicates.

<table><thead><tr><th></th><th>Starting P/P<br>D/(D + H)</th><th>D₂O<br>D/(D + H)</th></tr></thead><tbody><tr><td>Phenanthrene</td><td>1.38 ± 0.78 × 10⁻⁴ (6)</td><td>5.89 ± 0.57 × 10⁻³ (4)</td></tr><tr><td>Pyrene</td><td>1.39 ± 0.78 × 10⁻⁴ (6)</td><td>1.02 ± 0.23 × 10⁻² (4)</td></tr></tbody></table>

<figure><img src="image_6.png" /><figcaption>Fig. 4. Comparison of the yield of the experiment with and without saponite. PAHs are recovered in the soluble fraction (white) or in the solid phase (black).</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>**Fig. 3.** Carbon isotope values of phenanthrene and pyrene before and after 150 °C alteration experiments in the presence of pure ¹³C materials. No carbon isotope exchange is observed. Error bars represent standard deviations.</figcaption></figure>
compositions defining a negative trend with increasing PAH size (Gil-
mour and Pillinger, 1994; Naraoka et al., 2000). The similar trend
observed for PAHs in CCs have led authors to suggest that PAHs found in
CCs were produced in the ISM (Sephton et al., 1998; Gilmour and Pil-
linger, 1994; Naraoka et al., 2000; Huang et al., 2015; Lecasble et al.,
2022). Strengthening this hypothesis, the laboratory experiments con-
ducted in the present study showed that the carbon isotope composition
of PAHs does not change under asteroidal conditions (i.e. 150 °C), even
in the presence of other carbon reservoirs, either organic or inorganic.
This is consistent with individual PAHs having quite the same carbon
isotope signature in different CCs (Sephton et al., 1998; Gilmour and
Pillinger, 1994; Naraoka et al., 2000; Huang et al., 2015; Lecasble et al.,
2022). However, small variations remain: the same PAHs do not exhibit
the exact same carbon isotope compositions in different CCs. This sug-
gests either that the carbon isotopic composition of PAHs may slightly
change after their production under conditions not simulated here, or
that some of the PAHs have been produced via other pathways, possibly
including the destruction of larger PAHs.

Results are different for the hydrogen isotope compositions. The
PAHs produced in the ISM are expected to be deuterium-rich (Alla-
mandola et al., 1989; Tielens and Charnley, 1997; Millar et al., 2000;
Peeters et al., 2004; Salama, 2008) while the PAHs found in CCs contain
less deuterium than most of the organic components investigated to far,
like amino acids and IOM (Oba and Naraoka, 2003; Elsila et al., 2012;
Huang et al., 2015; Lecasble et al., 2022; Graham et al., 2022). A cause
of this discrepancy could be the effect of aqueous alteration on the
parent body. Strengthening this hypothesis, Oba and Naraoka (2003)
showed that hydrogen isotope composition of PAHs could evolve under
acidic conditions (pH = 2). The present study demonstrates that D-ex-
change with water can occur in less acidic conditions (starting water pH
between 4 and 5) at temperatures typical of asteroidal alteration (i.e.
150 °C). A recent study has reported that the water which circulated
onto the CM parent body was D-poor (Piani et al., 2021), which would
explain why the PAHs found in CMs are poor in D despite a possible
interstellar origin (Lecasble et al., 2022). However, a large range of δD
values has been reported in the literature for PAHs in CCs, from very
negative values (Oba and Naraoka, 2003; Graham et al., 2022; Lecasble
et al., 2022) to very positive values (Huang et al., 2015; Graham et al.,
2022). For instance, the δD value of pyrene extracted from Murchison
varies by >750 ‰ among different studies (Oba and Naraoka, 2003;
Huang et al., 2015; Graham et al., 2022), highlighting the need for more
data to accurately interpret the hydrogen isotope compositions of PAHs
in CCs. In addition, the present experiments showed that the extent of
isotope exchange varies with the size of the PAH, pyrene getting more D-
rich than phenanthrene after 7 days in D₂O at 150 °C. Although this
would need confirmation, such a result sheds new light on the negative
correlation between the sizes and the δD values of PAHs in CCs recently
reported by Graham et al. (2022). These authors interpreted this anti-
correlation as resulting from preferential enrichment of low molecular
weight gas-phase PAHs by unimolecular photodissociation before ac-
cretion. Alternatively, as shown here, this anti-correlation may result
from hydrogen isotope exchange between PAHs and water during
aqueous alteration onto asteroids.

4.3. Influence of the presence of clay minerals

Phyllosilicates are major constituents of carbonaceous chondrites (Pearson et al., 2006; Garvie and Buseck, 2007) and may significantly influence organic reactions (Vinogradoff et al., 2020a, 2020b; Viennet et al., 2022). However, their possible role on the molecular evolution of PAHs under hydrothermal conditions has only been understudied. Watson and Sephton (2015) showed that Fe-rich montmorillonite could enhance PAH polymerization in a dry environment at temperatures typical of that experienced by CCs. But Fe-rich montmorillonites have only been detected in CAIs of some CV chondrites (Tomeoka and Buseck, 1982), the phyllosilicates in CIs and CMs mostly being Fe—Mg

serpentines and Mg-smectites (i.e. saponites) (Brearley, 2006 and
reference therein). The laboratory experiments conducted here show
that the presence of saponite does not lead to the production of new
PAHs, confirming the experimental results of Giese et al. (2019) using
serpentine produced via the alteration of olivine.

However, a significant fraction of PAHs is not recovered at the end of
the experiments reported here. Most of the missing organic C seems to be
trapped within the solid residues which contain about 1.4 wt% of
organic carbon. These organics, whatever their nature, may either be
adsorbed onto saponites or trapped within their interlayer spaces as
previously reported by other experimental studies (Viennet et al., 2019,
2022). Ca-saturated smectites have the greatest adsorption capacities
(Hundal et al., 2001) and many sorption mechanisms between PAHs and
smectite have been proposed. These are hydrogen bonding between PAH
and the water film which surrounds smectite (Schwarzenbach et al.,
2003), hydrogen bonding between PAHs and intermediate polarity
mineral surface domains like silanols or aluminols (Hundal et al., 2001;
Lambert, 2018), noncovalent interaction between the positively charged
smectite and the π electrons of the PAH (Ma and Dougherty, 1997;
Mader et al., 1997) and capillary condensation of PAHs into nano and
micropores of a smectite platelet quasicrystal network (Hundal et al.,
2001; Müller et al., 2007). According to Hundal et al. (2001) and Müller
et al. (2007) the latter mechanism is the more efficient to sorb PAHs on
smectites.

In this study, we did not used saponification methods as they are
generally not used to extract PAHs from chondrites. However, whether
these trapped organics are PAHs or products of their degradation, as it
would be the case with reactive organics (Viennet et al., 2019, 2022;
Vinogradoff et al., 2020a, 2020b), such trapping of organic C by phyl-
losilicates may have biased the reported abundances of PAHs in CCs
(Pering and Ponnamperuma, 1971; Martins et al., 2015; Lecasble et al.,
2022), even if more efficient extraction methods were used. Here, more
pyrene than phenanthrene is missing in the soluble fraction at the end of
the experiment (only 77.8% of the initial pyrene was recovered versus
91.4% of the initial phenanthrene), suggesting that smectites may trap
large PAHS more efficiently. Extrapolating this result to large PAHs
similar to those detected in the ISM, trapping by phyllosilicates may be
invoked to explain their apparent absence in CCs.

More generally, the capabilities of smectites to trap organics, thereby
hampering their extraction (Viennet et al., 2022), may account for the
missing organic C paradox of CCs. Indeed, there is a difference between
TOC values and the sum of the IOM and SOM contents of most CIs and
CMs (Pearson et al., 2006; Alexander et al., 2015). This missing organic
C could consist in large PAHs similar to those detected in the ISM,
impossible to extract using solvents, but lost during acid leaching hence
not recovered within the IOM. In any case, the present experimental
results show that PAHs of CCs can be used as tracers of both pre-
accretion and secondary processes. This work also pleads for addi-
tional experiments in the presence of phyllosilicates to further explore
their influence on the signals carried by organic compounds in CCs.

Declaration of Competing Interest

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

Data availability

Data will be made available on request.

Acknowledgments

This study was funded by the European Research Council through
the ERC consolidator grant HYDROMA (grant agreement No. 819587).
References

Abdel-Shafy, H.I., Mansour, M.S., 2016. A review on polycyclic aromatic hydrocarbons: source, environmental impact, effect on human health and remediation. Egypt. J. Pet. 25, 107-123.

Alexander, R., Kagi, R.I., Larcher, A.V., 1982. Clay catalysis of aromatic hydrogen-exchange reactions. Geochim. Cosmochim. Acta 46, 219-222.

Alexander, C.M.O.'D., Bowden, R., Fogel, M.L., Howard, K.T., 2015. Carbonate abundances and isotopic compositions in chondrites. Meteorit. Planet. Sci. 50, 810-833.

Allamandola, L.J., Tielens, A.G.G.M., Barker, J.R., 1985. Polycyclic aromatic hydrocarbons and the unidentified infrared emission bands - auto exhaust along the milky way. Astrophys. J. 290, L25-L28.

Allamandola, L.J., Sandford, S.A., Wopenka, B., 1987. Interstellar polycyclic aromatic hydrocarbons and carbon in interplanetary dust particles and meteorites. Science 237, 56-59.

Allamandola, L.J., Tielens, A.G.G.M., Barker, J.R., 1989. Interstellar polycyclic aromatic hydrocarbons - the infrared emission bands, the excitation/emission mechanism, and the astrophysical implications. Astrophys. J. Suppl. Ser. 71, 733-775.

Anderson, D.E., Bergin, E.A., Blake, G.A., Ciesla, F.J., Visser, R., Lee, J.E., 2017. Destruction of refractory carbon in protoplanetary disks. Astrophys. J. 845, 13-27.

Brearley, A.J., 2006. The action of water. In: Lauretta, D.S., McSween Jr., H.Y. (Eds.), Meteorites and the Early Solar System II. University of Arizona Press, Tucson, pp. 587-624.

Changela, H.G., Le Guillou, C., Bernard, S., Brearley, A.J., 2018. Hydrothermal evolution of the morphology, molecular composition, and distribution of organic matter in CR (Renazzo-type) chondrites. Meteorit. Planet. Sci. 53, 1006-1029.

Cherchneff, I., Barker, J.R., Tielens, A.G., 1992. Polycyclic aromatic hydrocarbon formation in carbon-rich stellar envelopes. Astrophys. J. 401, 269-287.

Cody, G.D., Heying, E., Alexander, C.M.O.'D., Nittler, L.R., Kilcoyne, A.D., Sandford, S. A., Stroud, R.M., 2011. Establishing a molecular relationship between chondritic and cometary organic solids. Proc. Natl. Acad. Sci. 108, 19171-19176.

Dalgarno, A., Lepp, S., 1984. Deuterium fractionation mechanisms in interstellar clouds. Astrophys. J. 287, 47-50.

Derenne, S., Robert, F., 2010. Model of molecular structure of the insoluble organic matter isolated from Murchison meteorite. Meteorit. Planet. Sci. 45, 1461-1475.

Derenne, S., Rouzaud, J.N., Clinard, C., Robert, F., 2005. Size discontinuity between interstellar and chondritic aromatic structures: A high-resolution transmission electron microscopy study. Geochim. Cosmochim. Acta 69, 3911-3917.

Elsila, J.E., de Leon, N.P., Buseck, P.R., Zare, R.N., 2005. Alkylation of polycyclic aromatic hydrocarbons in carbonaceous chondrites. Geochim. Cosmochim. Acta 69, 1349-1357.

Elsila, J.E., Charnley, S.B., Burton, A.S., Glavin, D.P., Dworkin, J.P., 2012. Compound-specific carbon, nitrogen, and hydrogen isotopic ratios for amino acids in CM and CR chondrites and their use in evaluating potential formation pathways. Meteorit. Planet. Sci. 47, 1517-1536.

Fujiy a, W., 2018. Oxygen isotopic ratios of primordial water in carbonaceous chondrites. Earth Planet. Sci. Lett. 481, 264-272.

Garvie, L.A., Buseck, P.R., 2007. Prebiotic carbon in clays from Orqueil and Ivuna (CI), and Tagish Lake (C2 ungrouped) meteorites. Meteorit. Planet. Sci. 42, 2111-2117.

Giese, C.-C., Ten Kate, I.L., Plümper, O., King, H.E., Lenting, C., Liu, Y., Tielens, A.G.G. M., 2019. The evolution of polycyclic aromatic hydrocarbons under simulated inner asteroid conditions. Meteorit. Planet. Sci. 54, 1930-1950.

Gilmour, I., Pillinger, C.T., 1994. Isotopic compositions of individual polycyclic aromatic hydrocarbons from the Murchison meteorite. Mon. Not. R. Astron. Soc. 269, 235-240.

Graham, H.V., Elsila, J.E., Dworkin, J.P., Sandford, S.A., Aponte, J.C., 2022. Deuterium isotope fractionation of polycyclic aromatic hydrocarbons in meteorites as an Indicator of interstellar/Protosolar processing history. Life 12, 1368.

Greenberg, J.M., Gillette, J.S., Caro, G.M.M., Mahajan, T.B., Zare, R.N., Li, A., Schutte, W.A., de Groot, M., Mendoza-Gómez, C., 2000. Ultraviolet photoprocessing of interstellar dust mantles as a source of polycyclic aromatic hydrocarbons and other conjugated molecules. Astrophys. J. 531, L71.

Hagiwara, M., Nomoto, S., Shimoyama, A., 2000. Experimental simulation of thermal alteration of naphthalenes in sediments based on isomerization of methyl-and dimethylnaphthalenes. Res. Organic Geochem. 15, 43-50.

Hahn, J.H., Zenobi, R., Bada, J.L., Zare, R.N., 1988. Application of two-step laser mass spectrometry to cosmogeochemistry: direct analysis of meteorites. Science 239, 1523-1525.

Huang, Y., Aponte, J.C., Zhao, J., Tarozo, R., Hallmann, C., 2015. Hydrogen and carbon isotopic ratios of polycyclic aromatic compounds in two CM2 carbonaceous chondrites and implications for prebiotic organic synthesis. Earth Planet. Sci. Lett. 426, 101-108.

Hundal, L.S., Thompson, M.L., Laird, D.A., Carmo, A.M., 2001. Sorption of phenanthrene by reference smectites. Environ. Sci. Technol. 35, 3456-3461.

Kerridge, J.F., 1983. Isotopic composition of carbonaceous-chondrite kerogen: evidence for an interstellar origin of organic matter in meteorites. Earth Planet. Sci. Lett. 64, 186-200.

Krot, A.N., Hutcheon, I.D., Brearley, A.J., Pravdivtseva, O.V., Petaev, M.I., Hohenberg, C. M., 2006. Timescales and settings for alteration of chondritic meteorites. In: Lauretta, D.S., McSween Jr., H.Y. (Eds.), Meteorites and the Early Solar System II. University of Arizona Press, Tucson, pp. 525-553.

Lambert, J.F., 2018. Organic pollutant adsorption on clay minerals. In: Developments in Clay Science, vol. 9. Elsevier, pp. 195-253.

Le Guillou, C., Brearley, A., 2014. Relationships between organics, water and early stages of aqueous alteration in the pristine CR3. 0 chondrite MET 00426. Geochim. Cosmochim. Acta 131, 344-367.

Lecasble, M., Remusat, L., Viennet, J.C., Laurent, B., Bernard, S., 2022. Polycyclic aromatic hydrocarbons in carbonaceous chondrites can be used as tracers of both pre-accretion and secondary processes. Geochim. Cosmochim. Acta 335, 243-255.

Lee, J.E., Bergin, E.A., Nomura, H., 2010. The solar nebula on fire: A solution to the carbon deficit in the inner solar system. Astrophys. J. Lett. 710, L21.

Leger, A., Puget, J.L., 1984. Identification of the "unidentified" IR emission features of interstellar dust? Astron. Astrophys. 137, L5-L8.

Lentfort, S., Bischoff, A., Ebert, S., Patzek, M., 2021. Classification of CM chondrite breccias-implications for the evaluation of samples from the OSIRIS-REx and Hayabusa 2 missions. Meteorit. Planet. Sci. 56, 127-147.

Ma, J.C., Dougherty, D.A., 1997. The cation – *π* interaction. Chem. Rev. 97, 1303-1324.

Mader, B.T., Uwe-Goss, K., Eisenreich, S.J., 1997. Sorption of nonionic, hydrophobic organic chemicals to mineral surfaces. Environ. Sci. Technol. 31, 1079-1086.

Martins, Z., Modica, P., Zanda, B., Le Sergeant, d'Hendecourt L., 2015. The amino acid and hydrocarbon contents of the Paris meteorite: insights into the most primitive CM chondrite. Meteorit. Planet. Sci. 50, 926-943.

McSween, H.Y., 1979. Alteration in CM carbonaceous chondrites inferred from modal and chemical variations in matrix. Geochim. Cosmochim. Acta 43, 1761-1770.

Michoulier, E., Noble, J.A., Simon, A., Mascetti, J., Toubin, C., 2018. Adsorption of PAHs on interstellar ice viewed by classical molecular dynamics. Phys. Chem. Chem. Phys. 20, 8753-8764.

Millar, T.J., Roberts, H., Markwick, A.J., Charnley, S.B., 2000. The role of H2D+ in the deuteration of interstellar molecules. In: Philosophical Transactions of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences, 358, pp. 2535-2547.

Müller, S., Totsche, K.U., Kögel-Knabner, I., 2007. Sorption of polycyclic aromatic hydrocarbons to mineral surfaces. Eur. J. Soil Sci. 58, 918-931.

Naraoka, H., Shimoyama, A., Harada, K., 2000. Isotopic evidence from an Antarctic carbonaceous chondrite for two reaction pathways of extraterrestrial PAH formation. Earth Planet. Sci. Lett. 184, 1-7.

Oba, Y., Naraoka, H., 2003. A different behavior of hydrogen isotope exchange in aqueous solutions between two PAH isomers (fluoranthene and pyrene). Researches in organic geochemistry 18, 29-35.

Pearson, V.K., Sephton, M.A., Franchi, I.A., Gibson, J.M., Gilmour, I., 2006. Carbon and nitrogen in carbonaceous chondrites: elemental abundances and stable isotopic compositions. Meteorit. Planet. Sci. 41, 1899-1918.

Peeters, E., Allamandola, L.J., Bauschlicher Jr., C.W., Hudgins, D.M., Sandford, S.A., Tielens, A.G.G.M., 2004. Deuterated interstellar polycyclic aromatic hydrocarbons. Astrophys. J. 604, 252.

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

Pering, K.L., Ponnamperuma, C., 1971. Aromatic hydrocarbons in the Murchison meteorite. Science 173, 237-239.

Piani, L., Marrocchi, Y., Vacher, L.G., Yurimoto, H., Bizzarro, M., 2021. Origin of hydrogen isotopic variations in chondritic water and organics. Earth Planet. Sci. Lett. 567, 117008.

Pizzarello, S., 2006. The chemistry of life's origin: A carbonaceous meteorite perspective. Acc. Chem. Res. 39, 231-237.

Plows, F.L., Elsila, J.E., Zare, R.N., Buseck, P.R., 2003. Evidence that polycyclic aromatic hydrocarbons in two carbonaceous chondrites predate parent-body formation. Geochim. Cosmochim. Acta 67, 1429-1436.

Remusat, L., 2015. Organics in primitive meteorites. In: Lee, M.R., Leroux, H. (Eds.), Planetary Mineralogy. The European Mineralogical Union, pp. 33-65.

Richter, H., Howard, J.B., 2000. Formation of polycyclic aromatic hydrocarbons and their growth to soot—a review of chemical reaction pathways. Prog. Energy Combust. Sci. 26, 565-608.

Sabbah, H., Bonnamy, A., Papanastasiou, D., Cernicharo, J., Martín-Gago, J.A., Joblin, C., 2017. Identification of PAH isomeric structure in cosmic dust analogs: the AROMA setup. Astrophys. J. 843, 34.

Sabbah, H., Carlos, M., Jenniskens, P., Shaddad, M.H., Duprat, J., Goodrich, C.A., Joblin, C., 2022. Detection of cosmic fullerenes in the Almahata Sitta meteorite: are they an interstellar heritage? Astrophys. J. 931, 91.

Sagan, C., Khare, B.N., 1979. Tholins: organic chemistry of interstellar grains and gas. Nature 277, 102-107.

Salama, F., 2008. PAHs in astronomy-a review. In: Proceedings of the International Astronomical Union, 4, pp. 357-366.

Sandford, S.A., 2002. Interstellar processes leading to molecular deuterium enrichment and their detection. Planet. Space Sci. 50, 1145-1154.

Schimmelmann, A., Lewan, M.D., Wintsch, R.P., 1999. D/H isotope ratios of kerogen, bitumen, oil, and water in hydrous pyrolysis of source rocks containing kerogen types I, II, IIS, and III. Geochim. Cosmochim. Acta 63, 3751-3766.

Schwarzenbach, R.P., Gschwend, P.M., Imboden, D.M., 2003. Environmental Organic Chemistry, 2nd edn. Wiley, New York.

Septon, M.A., Pillinger, C.T., Gilmour, I., 1998. $^{13}$C of free and macromolecular aromatic structures in the Murchison meteorite. Geochim. Cosmochim. Acta 62, 1821-1828.

Sessions, A.L., Burgoyne, T.W., Hayes, J.M., 2001. Determination of the H3 factor in hydrogen isotope ratio monitoring mass spectrometry. Anal. Chem. 73, 200-207.

Shiu, W.-Y., Ma, K.-C., 2000. Temperature dependence of physical-chemical properties of selected chemicals of environmental interest. I. Mononuclear and polynuclear aromatic hydrocarbons. J. Phys. Chem. Ref. Data 29, 41-130.
Shock, E.L., Schulte, M.D., 1990. Amino-acid synthesis in carbonaceous meteorites by aqueous alteration of polycyclic aromatic hydrocarbons. Nature 343, 728-731.

Slavicinska, K., Duca, D., Egorov, D., Mitra, T., Carpentier, Y., Focsa, C., Bennett, C.J., Pirim, C., 2022. Link between polycyclic aromatic hydrocarbon size and aqueous alteration in carbonaceous chondrites revealed by laser mass spectrometry. ACS Earth and Space Chem. 6, 1413-1428.

Suttle, M.D., King, A.J., Schofield, P.F., Bates, H., Russell, S.S., 2021. The aqueous alteration of CM chondrites, a review. Geochim. Cosmochim. Acta 299, 219-256.

Suttle, M.D., King, A.J., Ramkissoon, N.K., Bonato, E., Franchi, I.A., Malley, J., Schofield, P.F., Najorka, J., Salge, T., Russell, S.S., 2022. Alteration conditions on the CM and CV parent bodies—insights from hydrothermal experiments with the CO chondrite Kainsaz. Geochim. Cosmochim. Acta 318, 83-111.

Takir, D., Emery, J.P., McSween Jr., H.Y., Hibbitts, C.A., Clark, R.N., Pearson, N., Wang, A., 2013. Nature and degree of aqueous alteration in CM and CI carbonaceous chondrites. Meteorit. Planet. Sci. 48, 1618-1637.

Tielens, A.G.G.M., 2008. Interstellar polycyclic aromatic hydrocarbon molecules. Annu. Rev. Astron. Astrophys. 46, 289-337.

Tielens, A.G.G.M., 2011. 25 years of PAH hypothesis. In: Joblin, C., Tielens, A.G.G.M. (Eds.), PAHs and the Universe, 46. EAS Publication Series, pp. 3-10.

Tielens, A.G.G.M., Charnley, S.B., 1997. Circumstellar and interstellar synthesis of organic molecules. In: Whittet, D.C.B. (Ed.), Planetary and Interstellar Processes Relevant to the Origins of Life. Springer, Dordrecht, pp. 23-51.

Tomeoka, K., Buseck, P.R., 1982. Intergrown mica and montmorillonite in the Allende carbonaceous chondrite. Nature 299, 326-327.

Turner, S., McGee, L., Humayun, M., Creech, J., Zanda, B., 2021. Carbonaceous chondrite meteorites experienced fluid flow within the past million years. Science 371, 164-167.

Verdier-Paoletti, M.J., Marrocchi, Y., Avice, G., Roskosz, M., Gurenko, A., Gounelle, M., 2017. Oxygen isotope constraints on the alteration temperatures of CM chondrites. Earth Planet. Sci. Lett. 458, 273-281.

Viennet, J.C., Bernard, S., Le Guillou, C., Jacquemot, P., Balan, E., Delbes, L., Rigaud, B., Georgelin, T., Jaber, M., 2019. Experimental clues for detecting biosignatures on Mars. Geochem. Perspect. Lett. 12, 28-33.

Viennet, J.C., Le Guillou, C., Remusat, L., Baron, F., Delbes, L., Blanchenet, A.M., Laurent, B., Criouet, I., Bernard, S., 2022. Experimental investigation of Fe-clay/ organic interactions under asteroidal conditions. Geochim. Cosmochim. Acta 318, 352-365.

Vinogradoff, V., Le Guillou, C., Bernard, S., Binet, L., Cartigny, P., Brearley, A.J., Remusat, L., 2017. Paris vs. Murchison: impact of hydrothermal alteration on organic matter in CM chondrites. Geochim. Cosmochim. Acta 212, 234-252.

Vinogradoff, V., Bernard, S., Le Guillou, C., Remusat, L., 2018. Evolution of interstellar organic compounds under asteroidal hydrothermal conditions. Icarus 305, 358-370.

Vinogradoff, V., Le Guillou, C., Bernard, S., Viennet, J.-C., Jaber, M., Remusat, L., 2020a. Influence of phyllosilicates on the hydrothermal alteration of organic matter in asteroids: experimental perspectives. Geochim. Cosmochim. Acta 269, 150-166.

Vinogradoff, V., Remusat, L., McLain, H.L., Aponte, J.-C., Bernard, S., Danger, G., Dworkin, J.P., Elsila, J.E., Jaber, M., 2020b. Impact of phyllosilicates on amino acid formation under asteroidal conditions. ACS Earth and Space Chem. 4, 1398-1407.

Watson, J.S., Sephton, M.A., 2015. Heat, aromatic units, and iron-rich phyllosilicates: a mechanism for making macromolecules in the early solar system. Astrobiology 15, 787-792.

Wing, M.R., Bada, J.L., 1991a. The origin of the polycyclic aromatic hydrocarbons in meteorites. Orig. Life Evol. Biosph. 21, 375-383.

Wing, M.R., Bada, J.L., 1991b. Geochromatography on the parent body of the carbonaceous chondrite Ivuna. Geochim. Cosmochim. Acta 55, 2937-2942.

Yang, J., Epstein, S., 1983. Interstellar organic matter in meteorites. Geochim. Cosmochim. Acta 47, 2199-2216.

Yang, J., Epstein, S., 1984. Relic interstellar grains in Murchison meteorite. Nature 311, 544-547.

Yesiltas, M., Kebukawa, Y., 2016. Associations of organic matter with minerals in Tagish Lake meteorite via high spatial resolution synchrotron-based FTIR microspectroscopy. Meteorit. Planet. Sci. 51, 584-595.

Zolotov, M.Y., 2012. Aqueous fluid composition in CI chondritic materials: chemical equilibrium assessments in closed systems. Icarus 220, 713-729.