A&A 650, A160 (2021) https://doi.org/10.1051/0004-6361/202039991 Astronomy & © V. Cabedo et al. 2021 Astrophysics Study of Fischer–Tropsch-type reactions on chondritic meteorites V. Cabedo1,3 , J. Llorca2 , J. M. Trigo-Rodriguez3,4 , and A. Rimola5 1 Astrophysics department, CEA/DRF/IRFU/DAp, Université Paris Saclay, UMR AIM, 91191 Gif-sur-Yvette, France e-mail: victoria.cabedo@cea.fr 2 Institut de Tècniques Energètiques and Departament d’Enginyeria Química, Universitat Politècnica de Catalunya, Barcelona, Catalonia, Spain 3 Institute of Space Sciences (CSIC), Meteorites, Minor Bodies and Planetary Sciences Group, Campus UAB, Carrer de Can Magrans, s/n, 08193, Barcelona, Catalonia, Spain 4 Institut d’Estudis Espacials de Catalunya (IEEC), Gran Capità, 2 - baix, 08034, Barcelona, Catalonia, Spain 5 Departament de Química, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia, Spain Received 25 November 2020 / Accepted 11 May 2021 ABSTRACT Context. How simple organic matter appeared on Earth and the processes by which it transformed into more evolved organic com- pounds, which ultimately led to the emergence of life, is still an open topic. Different scenarios have been proposed, the main one assumes that simple organic compounds were synthesized, either in the gas phase or on the surfaces of dust grains, during the process of star formation and they were incorporated into larger bodies in the protoplanetary disk. The transformation of these simple organic compounds in more complex forms is still a matter of debate. Recent discoveries have pointed to catalytic properties of dust grains present in the early stellar envelope, which can nowadays be found in the form of chondrites. The significant infall of chondritic mete- orites during the early periods of Earth suggests that the same reactions could have taken place in certain environments on the Earth’s surface, with conditions more favorable for organic synthesis. Aims. This work attempts to synthesize simple organic molecules, such as hydrocarbons and alcohols via Fischer–Tropsch-type reac- tions supported by different chondritic materials under early-Earth conditions, to investigate if organic synthesis can likely occur in this environment and to determine what the differences are in selectivity when using different types of chondrites. Methods. Fischer–Tropsch-type reactions are investigated from mixtures of CO and H2 at 1 atm of pressure on the surfaces of different chondritic samples. The different products obtained are analyzed in situ by gas chromatography. Results. Different Fischer–Tropsch reaction products are obtained in quantitative amounts. The formation of alkanes and alkenes being the main processes. The formation of alcohols also takes place in a smaller amount. Other secondary products were obtained in a qualitative way. Conclusions. Chondritic material surfaces have been proven as good supports for the occurrence of organic synthesis. Under certain circumstances during the formation of Earth, they could have produced a suitable environment for these reactions to occur. Key words. astrochemistry – meteorites, meteors, meteoroids – planetary nebulae: general 1. Introduction instance, have been repeatedly observed from starless cores to star forming regions (Vasyunina et al. 2014; López-Sepulcre Life on Earth likely arose from a series of particular condi- et al. 2015; Bianchi et al. 2018; McGuire 2018; van Gelder et al. tions, which have yet to be unambiguously determined. It has 2020). Robust pieces of evidence indicate that the formation of been envisioned that the early Earth was exposed to different iCOMs takes place on the surface of interstellar grains (Kress sources of energy, such as light, heat, and reduction–oxidation & Tielens 2001; Sekine et al. 2006; Linnartz et al. 2015; Oberg (redox) potentials. Such an environment also received a large 2016, Enrique-Romero et al. 2019; Zamirri et al. 2019; Martín- flux of extraterrestrial material, at least until the end of the late Doménech et al. 2020), which with time will coagulate and form heavy bombardment (LHB, Bottke et al. 2012). At some point, the embryos of rocky planets and minor bodies. the conditions in the atmosphere and surface of our planet might Chondrites are a class of meteorites that come from undif- have promoted an increase in molecular complexity (Rotelli et al. ferentiated bodies (they never melted), such as small asteroids 2016) which, later on, allowed the recombination of organic or comets, and they have suffered very low chemical or ther- molecules to form more complex, interacting and self-replicating mal alteration processes (Zolensky et al. 2008). Chondrites come systems (Walde 2005; Shulze-Makuch & Irwin 2008). from the direct accretion of the primordial materials forming the The synthesis of interstellar complex organic molecules protoplanetary disk, so they are believed to be the most pris- (iCOMs) in the solar nebula and during the process of star for- tine samples of the dust grains forming our early Solar System mation has been extensively studied during recent years (Herbst (Weisberg et al. 2006; Trigo-Rodriguez 2015) preserving their 2017). The simplest organic compounds, such as formaldehyde primordial components: metal grains, sulfides, and igneous (H2 CO) and methanol (CH3 OH), and other iCOMS, includ- silicate-rich spherules called chondrules (hence the name chon- ing acetaldehyde (CH3 CHO) and formamide (NH2 CHO) for drites). Particularly interesting are carbonaceous chondrites A160, page 1 of 23 Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. A&A 650, A160 (2021) (CCs) since they contain about 1–4% of carbon in mass If FTT reactions can be extrapolated to environments similar (Remusat et al. 2007; Alexander et al. 2017), which is found in to the available conditions present in the primeval Earth, chon- the form of organic matter aggregates (Trigo-Rodriguez et al. dritic meteorites could be responsible not only for bringing large 2019). This organic matter is thought to have been synthesized amounts of organic material and water to the protoplanet, but in the solar nebula, some of these reactions being catalyzed by also for promoting reactions of paramount astrobiological rel- the surfaces of the metallic phase present in the dust (Llorca & evance in the emergence of prebiotic chemistry. Therefore, the Casanova 2000). aim of this work is to explore this possibility by simulating FTT Surface reactions in solid-dry environments can play a cen- processes in an environment similar to the primeval atmosphere tral role in the synthesis of biomolecular precursors and other of Earth. large complex organic molecules of extrasolar origin, which have been identified in undifferentiated meteorites (Ehrenfreund & Charnley 2000; Sephton 2002; Botta & Bada 2002). Indeed, dif- 2. Experimental procedure ferent studies demonstrate that important prebiotic molecules, 2.1. Sample description and preparation including amino acids (Bernstein et al. 2002; Muñoz Caro et al. 2002; Elsila et al. 2007; Nuevo et al. 2008; Lee et al. 2009), can Two different meteoritic samples were used to prove their sur- be formed by processing of interstellar ices (Ciesla & Sandford face activity, provided by different collections and chosen by 2012; Fedoseev et al. 2015, 2017; Chuang et al. 2015, 2017). More their availability. Samples of CCs and ordinary chondrites (OCs) recently, nonenergetic ice chemistry (i.e., without the need of have been chosen because of their primitive composition, with energetic external triggers processing the ice) has been shown an isotopic composition similar to solar, and their relative low to be also operative in the formation of glycine (Krasnokutski degree of alteration. These characteristics make them good et al. 2020; Ioppolo et al. 2021). However, investigations on the exemplars of the dust present in the protoplanetary disk. More- synthesis of prebiotic compounds on meteoritic minerals and/or over, both classes cover an important percentage of the recovered analogs under dry conditions (i.e., through gas-surface reactions) meteorites that fall into Earth’s surface, and therefore, by extrap- is practically missing. olation, they are also good examples of the kind of materials that Since H2 and CO are the most abundant gas-phase com- fell during the early stages of Earth’s formation. pounds in most of the astrophysical environments, along with KG 007 is an OC of subtype H and petrological type 6 the fact that metallic components usually used as catalytic sup- (Ruzicka et al. 2014). Those are distinguished by presenting ports are commonly found in meteoritic materials, gas-surface subsolar Mg/Si and refractory/Si ratios, to exhibit oxygen iso- Fischer–Tropsch-type (FTT) reactions are invoked here as possi- tope composition above the terrestrial fractionation line and to ble synthetic routes for part of the organic content (i.e., hydrocar- contain a large volume percentage of chondrules, with only 10– bons and alcohols) identified in these asteroidal bodies (Ferrante 15 vol.% of a fine-grained matrix (Weisberg et al. 2006). They et al. 2000; Sekine et al. 2006). The Fischer–Tropsch synthesis do not contain organic matter in their matrix. The H (high-iron) consists of a set of chemical reactions that produce hydrocar- group of OCs are characterized by their high siderophile element bons and fuels from mixtures of CO and H2 (see Eqs. (1) and content, with a metal abundance of around 8 vol.%. Petrological (2)). Additionally, it can also produce secondary reactions such type 6 designates chondrites that have suffered metamorphism as the formation of alcohols (Eq. (3)) or the disproportion of CO under conditions sufficient to homogenize all mineral composi- (Eq. (4), Schulz 1999; Mahmoudi et al. 2017). FTT processes tions, but melting did not occur and therefore there is no phase proceed under the presence of a metal catalyst, generally Fe, differentiation. KG 007 was obtained already grinded and in Co, Ni and Ru. The mechanism of the reaction and the prod- two different phases: one containing the full meteoritic compo- uct selectivity and distribution vary depending on the metal used sition (Sample B) and another one only containing the metallic as support and on the reaction conditions (Mahmoudi et al. 2017) inclusions separated by magnetic means (Sample C). as follows: NWA 801 is a CC of subtype R and petrologic type 2 (Connolly Jr. et al. 2007). CCs are very primitive materials that nCO(g) + (2n + 1)H2(g) Cn H2n+2(g) + nH2 O(g) (1) have Mg/Si ratios near solar values and oxygen isotope compo- sitions below the terrestrial fractionation line (Weisberg et al. 2006). The Renazzo subgroup (R) is distinguished by large and nCO(g) + (2n)H2(g) Cn H2n(g) + nH2 O(g) (2) abundant porphyritic chondrules (50 vol.%). It has few refrac- tory inclusions and an abundant metal percentage, between 5– nCO(g) + (2n)H2(g) C(n) H2n+1 OH(g) + (n − 1)H2 O(g) (3) 8 vol.%, and a fine-grained matrix, which is commonly hydrated occupying up to 50 vol.%. As mentioned above, they are impor- tant because they contain up to 4% of organic matter aggregates 2CO(g) C(s) + CO2(g) . (4) in their matrix (Remusat et al. 2007; Alexander et al. 2017; Trigo- Rodriguez et al. 2019). Petrological type 2 designates chondrites The advent of organic chemical reactions in primordial characterized by abundant hydrated minerals and an abundant grains of the solar nebula and the protoplanetary disk is of funda- fine-grained matrix, with Ni-bearing sulfides. NWA 801 (Sam- mental relevance as these materials were lately processed to form ple D) was obtained as a small chunk and was completely the seeds of planets, comets and meteorites (Brearley & Jones grinded before introducing it in the reactor, using a glass mor- 1998). Moreover, the flux of chondritic material was important tar until obtaining a very fine dust. Details on the petrology and during the early periods of the Earth, which could provide the composition of each chondrite type used in the samples can be support and conditions necessary for these reactions to occur. found in Table 1. The vapor clouds produced by the impacts of these bodies and For each sample, 0.5 g of meteoritic dust was mixed with the presence of these particular metal alloys, with the high pres- 2.5 g of SiC, a very inert compound which assured a constant sure and high temperature conditions, could have established an volume of the samples so the contact time between the reac- adequate environment for complex chemistry to take place. tants and the samples was optimized to maximize the reaction A160, page 2 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Table 1. Average petrologic characteristics of the chondrite groups used in this work. Type Chondrule abund. (∗) Matrix abund. CAI abund. Metal abund. Average chondrule diameter Organic content (vol.%) (vol.%) (vol.%) (vol.%) (mm) (wt%) CR 50–60 30–50 0.5 5–8 0.7 0.8–2.6 H 60–80 10–15 1 8 0.3 0 Notes. Adapted from Weisberg et al. (2006). (∗) Chondrule abundance includes lithic and mineral fragments. Table 2. Sample description. Sample Meteorite Type Subtype Weight SiC weight Total weight Gas flow (g) (g) (g) A – – – – 3.0027 3.0027 H2 /CO B KG007 OC H6 0.5012 2.4996 3.0008 H2 /CO C KG007 OC H6 0.5158 2.4929 3.0087 H2 /CO (magnetic phase) D NWA 801 CC CR2 0.5256 2.4814 3.0070 H2 /CO E NWA 801 CC CR2 0.5060 2.4986 3.0046 Ar Notes. Instrumental errors are ±0.0001g. rate, assure reproductibility and allow for a comparison between the samples. Details on the sample preparations can be found in Table 2. Sample A was used as the blank analysis in order to follow the progress of the reactions without meteoritical samples and to assure that there is no chemical activity coming from SiC. Sample E was used as a second blank analysis, with a meteorit- ical content from NWA 801 but without passing CO and H2 as reactants and circulating Ar instead, in order to ensure that the detected products are not coming from the meteorite itself due to the presence of organic matter in the matrix of CCs. This proce- dure was not done for KG 007 because it is an OC and therefore Fig. 1. Schematic of the experimental setup. The CO and H2 were it does not contain any organic matter in the matrix. Due to the passed through the heated reactor containing the samples, and the relatively rare nature of the samples and the lack of enough mate- resulting gas was injected into the GC. rial, we were unable to produce duplicates of each sample and of each experiment. a 10 m STABILWAX for oxygenated compound analysis, and a MS5A for nonpolar compound analysis. Each product was 2.2. Fischer–Tropsch reactions quantified with calibration standards and using the GC software Soprane. Standards and reaction gases were supplied by Nippon The reaction conditions were the same for all the samples. The Gases and had a purity of 99.999%. total weight of the samples was introduced in a closed stainless- Reactions were carried out during ca. 3 h, though the time steel reactor with an internal diameter of 6 mm and a total varied depending on the stability of the production. Products volume of 5 mL and it was heated by a furnace, where a flux were analyzed continuously, with injections to the GC every of CO and H2 was circulated. The conditions were selected to 5 min. After each experiment, the reactor was cleaned with a resemble those present on the primitive surface of the Earth. brush, using only water and then dried in an oven at 200 ◦ C. The ratio of reactants was set to H2 :CO = 4, which is consistent with the estimated primitive ratios of the primitive atmosphere of Earth, that is H2 :CO = 0.03–10 (Kress & Tielens 2001). The 3. Results fluxes of the reactants were set to a total of 40 mL min−1 , with In the present experiments, the production of hydrocarbons has H2 = 32 mL min−1 and CO = 8 mL min−1 . For Sample E, Ar was been successfully achieved, in addition to other minor products circulated as an inert gas with a flux of 40 mL min−1 . Pressure such as primarily alcohols and other oxygenated compounds. was set to 1 atm to simulate the average pressure on Earth’s The percentage of products obtained was computed as the per- surface. Since the relevant production of FTT reactions starts at centage of CO that has been transformed in each different 400 K (Sekine et al. 2006), here the temperature was increased product, including the production of solid carbon, following manually from 200 to 600 ◦ C in steps of 50 ◦ C. Eq. (5): Products were analyzed online with an Agilent 3000A micro gas chromatography (GC) system. The GC is directly connected nP to the outlet of the reactor by stainless steel tubes. A schematic χP = × 100 nCO, R of the experimental setup is shown in Fig. 1. Three different nP (5) columns were used in order to be able to analyze products with = f × 100, different polarities: an 8 m PLOTU for hydrocarbon analysis, nCO − nCO i A160, page 3 of 23 A&A 650, A160 (2021) CH4 Production CH3OH Production Sample A Sample A 15 Sample B 0.06 Sample B Sample C Sample C 10 Sample D Sample D Sample E 0.04 Sample E 5 0.02 0 0.00 C2H6 Production (%) CH3CH2OH Production 2.5 0.03 2.0 1.5 0.02 (%) 1.0 0.5 0.01 0.0 C2H4 Production 0.00 200 250 300 350 400 450 500 550 600 1.00 T (ºC) 0.75 Fig. 3. Evolution of alcohol production with temperature. The CH3 OH 0.50 production (top) and CH3 CH2 OH production (bottom). 0.25 0.00 For Sample A the production of alkanes and alkenes only 200 250 300 350 400 450 500 550 600 start at higher temperatures than the other samples (at least T (ºC) 400 ◦ C). Moreover, the percentage of the compounds formed are significantly smaller than in the presence of the meteoritical sam- Fig. 2. Evolution of the production of hydrocarbons with temperature: ples, being particularly evident for the most abundant products of CH4 production (top), C2 H6 production (middle) and C2 H4 production the reaction (CH4 and C2 H6 ). These findings clearly provide evi- (bottom). dence for the negligible activity of SiC and they suggest that the activity detected is caused by the reaction occurring in the mete- where χP is the molar fraction of the formed product (in %), nP oritical samples. Sample E shows no production of any of the is the obtained mols of the formed product, and nCO, R are the aforementioned products, indicating that no desorption or out- mols of CO that have been consumed, which were computed as gassing of organics from the meteorite is detected under these the difference between the initial CO mols (niCO ) and the final conditions. CO mols detected (nfCO ). The obtained chromatograms for all the experiments are shown in Appendix A. 3.2. Alcohols production 3.1. Hydrocarbon production Figure 3 shows the production of alcohols during the experi- ments. The profiles are rather different than those for hydro- Figure 2 shows the evolution of the production of the differ- carbon production. The formation of CH3 OH starts at 350 ◦ C, ent hydrocarbons with temperature. In the different experiments, peaks at 400 ◦ C for all the samples, and it stops before reaching alkanes have been successfully synthesized, methane (CH4 ) and 550 ◦ C, depending on the sample. The production of alcohols ethane (C2 H6 ) being the primary and the secondary products. with longer carbon chains, mainly ethanol (CH3 CH2 OH), is For Samples B–D, the formation of CH4 starts at 300 ◦ C. For restricted to higher temperatures, starting at 400 ◦ C. The per- Samples B and C, such a production still works at higher temper- centage of CH3 CH2 OH starts to increase when CH3 OH starts atures than 600 ◦ C, while for Sample D it stops before reaching to decrease, indicating a sequential alcohol production (i.e., 550 ◦ C. CH3 CH2 OH can only form when the concentration of CH3 OH The production of C2 H6 also starts at 300 ◦ C, but it decreases is high enough). The maximum production is at 550 ◦ C for all at 550–600 ◦ C for Samples B and C. Whereas for Sample D, this samples except Sample D, which occurs at lower temperatures happens at 400 ◦ C. (450 ◦ C). The production of alkenes starts at a slightly higher temper- Some alcohols with even longer chains, such as propanol ature than that for alkanes (i.e., 350 ◦ C). For Samples B and C, (CH3 CH2 CH2 OH) and butanol (CH3 CH2 CH2 CH2 OH), are it starts to decrease when the temperature reaches 600 ◦ C while detected, but only in a qualitative way. This indicates that for Sample D it stops before reaching 550 ◦ C. The formation of the production of alcohols is not associated with the previous C2 H4 starts to be detected when some amount of C2 H6 was pro- production of hydrocarbons so that both products are formed duced and the maximum production of C2 H4 occurs upon the independently. No alcohols with an alkene chain have been decrease of C2 H6 suggesting that both mechanisms are corre- detected, which sustains this hypothesis. lated, meaning that alkene formation starts when the amount of The production of alcohols does not take place in Sample A alkanes in the catalyst surface is large enough. The formation or Sample E. This suggests again that the products detected are of alkynes is not detected, indicating that the energy barrier for being formed in the surface of the meteoritical material and that the formation of the triple-C bond is not surmountable even in they are not coming from the activity of SiC or the meteorites presence of the catalysts. themselves. A160, page 4 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites CO2 Production surface of the meteorites; and (iii) if the products were coming Sample A from the samples, their production would not be detected over 25 Sample B the extended time of the experiments. It should also be noted that Sample C while CCs do contain a very small amount of organic matter, and Sample D they could have been a possible source of contamination, OCs 20 Sample E do not present any detectable percentage of organic material; 15 accordingly, those detected here are being formed by processes (%) occurring in the reactor. 10 It has also been checked that the reaction is not taking place because of the presence of SiC, by doing a blank analysis (Sam- 5 ple A). Those results show that the formation of hydrocarbons is negligible in comparison with the samples that present mete- 0 oritic material, especially for the most abundant products CH4 200 250 300 350 400 450 500 550 600 and C2 H6 , and it only occurs at larger temperatures of at least T (ºC) 400 ◦ C. Additionally, they do not show formation of alcohols, which is observed in the meteoritic samples. Overall, it is clear Fig. 4. Evolution of CO2 production with temperature. that the detected products are coming from reactions occurring inside the reactor and not from the samples themselves and that 3.3. CO2 production and carbon deposition those reactions do not occur in the gas phase. The total conversion of CO in products with respect to solid We note that CO2 is continuously produced during the experi- carbon is relatively low, less than 25%, but it is large enough ments, as shown in Fig. 4. Its production starts at 250 ◦ C and to have quantitative results. In general, above 300 ◦ C, the pro- it keeps relatively constant during all the experiment, the per- duction of alkanes and alkenes is relatively important, with centage of which depends on the sample. In view of that, CO2 selectivities between 25 and 75% of the total product conver- formation does not depend on the previous formation of hydro- sion (without accounting for solid carbon). Furthermore, CO2 is carbons and/or alcohols. The production of CO2 is not detected also produced in large amounts, with a selectivity that goes down for Sample E, suggesting again there is no outgassing from the from 100 to 25% as the temperatures rises. Alcohols are also pro- meteorite matrix. duced, but in minor quantities, with selectivities not larger than The remaining percentage of the CO that has reacted but does 0.6%. Nevertheless, their formation is very important because not transform into products, and therefore does not appear in the it demonstrates the incorporation of O in O2 -free environments, percentage counting, is deposited on the surfaces of the meteorit- thereby forming polar groups that can result in molecules (i.e., ical samples as solid carbon, poisoning the surfaces, and, with CH3 CH2 CH2 CH2 OH and larger alcohols) of great importance time, likely preventing FTT reactions from taking place in an for prebiotic chemistry and biochemistry (Walde 2005). efficient way (Llorca & Casanova 1998). The evolution of the This work allowed us to distinguish the differences between surface poisoning is out of the scope of this paper. the two classes of chondrites (Samples B and D). The pro- duction of hydrocarbons starts at a slightly lower temperature 3.4. Other compounds for CCs than for OCs, though the percentage of products is roughly the same. The production of alcohols is similar as well, Other compounds were detected during the experiments, but although it should be noted that Sample D produces a larger their evolution was not quantified. These compounds are mainly amount of CH3 CH2 OH. The similarities observed are attributed formaldehyde (H2 CO) and acetone ((CH3 )2 CO). They are to the similar percentage of metallic inclusions in both chondrite formed at less than 400 ◦ C, most possibly as byproducts or types, while the differences are probably caused by their dif- intermediates of the FTT reactions. ferent metallic composition and the different alteration degrees suffered by the materials. The activity of the metallic inclusions has been analyzed 4. Analysis and discussion separately from the other phases (Sample C). The results indi- 4.1. Organic compound production on chondritic materials cate that the overall production is larger than for Samples B and D: it starts at lower temperatures and extends to larger tempera- In this work, it is proven that chondritic materials can support tures. Some exceptions are noted: (i) The production of C2 H4 is FTT reactions. First of all, it can be concluded that the organics lower for Sample C than for Sample D (NWA 801), and (ii) the detected do not come from the meteoritic samples. The non- CH3 OH production is low in comparison to the other samples. detection of any products on the blank (Sample E) proves that We attribute both events to a possible different composition of the detected products are formed by the interaction of the reac- the metallic phases, which can favor the formation of some prod- tants with the meteorite surfaces and that they do not come from ucts in detriment of others, that is the formation of C2 H4 is not as the desorption or the outgassing of the meteorite matrix. We favorable as C2 H6 for the metals present in Sample C, while the note other reasons that support that reactions are taking place in formation of CH3 OH is reduced in favor of a larger and faster for- the reactor: (i) The progressive decrease in the amount of CO mation of CH3 CH2 OH. Although in this work is not possible to detected in the GC with respect to the initial CO introduced directly correlate and quantify the activity with the metal content in the reactor suggests that the products are actually formed due to the lack of prior characterization of the complete compo- from the reactants and hence that they do not come from the sition of the meteoritical samples, our findings suggest that the meteorites themselves; (ii) the agreement of the distribution of metallic phases are responsible for most of the surface activity products with the one expected from FTT reactions, the fact that of the samples, in detriment of the silicate phase. Moreover, pre- no other species are detected, and the consecutive formation of vious experiments carried out by Ferrante et al. (2000), using products also indicate that the reactions are taking place on the silicate phase analogs alone, did not detect any FTT products, A160, page 5 of 23 A&A 650, A160 (2021) supporting the hypothesis that the metallic phase (Fe in their In small planets, such as Earth, when the protostellar envelope case) was responsible for the chemical activity. vanishes the first atmosphere is likely to escape and outgassing The results of the present work are in agreement with of the planet forms the secondary atmosphere. The large amount other works available in the literature. Under conditions resem- of impacts during the formation of Earth could have helped the bling those of the solar nebula (pressure ≈10−4 atm and emergence of this atmosphere since the volatilization of parts H2 :CO > 100:1), only hydrocarbons were produced, but with of the silicates of the mantle could have allowed the presence longer chains (C1 –C4 ) (Llorca & Casanova 1998). When using of volatile elements, for example CO, in the atmosphere for a Fe-doped silica instead, the experiments of Ferrante et al. relatively long time (Lammer et al. 2018). (2000), which were carried out under similar conditions to this A consequence of these processes is that even though work (pressure ≈1 bar and H2 :CO = 2–100), produced a simi- CO-containing atmospheres could not be stable, they proba- lar hydrocarbon distribution, finding CH4 , C2 H6 and C2 H4 as bly existed as steady states for periods long enough so CO the most abundant products. However, they also conclude that could react with H2 triggering FTT processes, as well as other the main activity occurred in the metallic phase. Other works fundamental reactions such as the Haber-Bosch (HB) synthe- also obtained more complex hydrocarbons under similar condi- sis (i.e., ammonia formation from N2 and H2 ), thereby giving tions (Gilmour et al. 2002), such as aromatic compounds, which rise to a richer and more complex chemistry in the planet sur- have not been produced in this work. It should be noted that face. These processes are envisioned to happen on vapor plumes none of these works reported the production of alcohols or other produced after the impact of meteorites on Earth’s surface oxygenated compounds. (Trigo-Rodríguez & Martín-Torres 2013; Lammer et al. 2018), The differences between the different works can be explained when reducing gases were locally released and the pressure and as follows. First, the experimental conditions are different. temperature were high enough. Here it is considered an Earth-like environment, that is to say larger pressures and H2 :CO = 4. As expected, larger pressures give faster reactions (reaction times of ∼3 h, this work and 5. Summary Ferrante et al. 2000 versus >102 h, Llorca & Casanova 1998). In this work, FTT reactions have been investigated in the pres- Moreover, our H2 :CO ratio probably favors the formation of ence of different meteoritical samples and under conditions alcohols in detriment of hydrocarbons (H2 :CO = 4, this work ver- resembling those of the early Earth. These laboratory exper- sus H2 :CO = 250, Llorca & Casanova 1998). Secondly, actual iments demonstrate that the undifferentiated meteorites can meteoritic samples are used while the cited works used synthetic act as a surface support to promote the synthesis of different metallic alloys. It is possible that alteration processes undergone organic compounds from H2 and CO mixtures. The following by the meteoritic materials produced structural and electronic conclusions have been reached: changes on their surfaces, giving rise to a different catalytic – FTT reactions can occur under planetary conditions with the behavior. In addition, meteoritic materials do not only contain surface support of chondritic materials; Fe in their composition, usually used as a metallic phase ana- – FTT reactions under these particular conditions yield the log, but also other metals, such as Ni or Co, which are known to synthesis of hydrocarbons (CH4 , C2 H6 and C2 H4 ) as well as have an effect on the selectivity and product distribution of FTT alcohols (CH3 OH and CH3 CH2 OH) and other oxygenated reactions (Mahmoudi et al. 2017). This could favor the formation compounds, such as H2 CO and (CH3 )2 CO even in O2 -free of oxygen-bearing compounds, which are not reported in other reaction conditions. A large amount of CO2 is also produced; works. In order to totally understand the effect of the different – The detection of products is associated with reactions hap- alteration degrees of the samples in the chemical outcome and pening on the surfaces of the meteorites and not due to the actual relationship between the metal quantity and the cat- the desorption of organic contents already present in the alytic activity, more similar experiments are needed using a more materials themselves. The activity is mainly associated with extensive sampling of chondrite types, which suffered different the metallic phases since they show larger productivity than degrees of alteration and contain other and different amounts of other mineral phases (e.g., silicates). metallic inclusions, such as CIs and CBs (which contain 0 vol.% We conclude that further work is needed to fully characterize and 60–80 vol.% abundance of metals, respectively). the possible catalytic properties of different chondrite types, with a special focus on the influence of the different percent- 4.2. The early Earth atmosphere and problems of the ages of metal inclusions and different alteration degrees, and to Fischer–Tropsch mechanism determine if these materials can also promote other reaction- types crucial for prebiotic chemistry, such as the HB synthesis One of the main conundrums to assess if these reactions could and further N2 chemistry or sulfur- and phosphorous-based have taken place in an early-Earth environment relies on the chemistry. real atmospheric composition at that time. The work by Miller and Urey (Miller 1953) assumed a strongly reducing atmo- Acknowledgments. J.M.T.-R. acknowledges financial support from research sphere, composed of H2 , CH4 , NH3 and H2 O, which is an ideal project PGC2018-097374-B-I00, funded by FEDER/Ministerio de Ciencia e Innovación – Agencia Estatal de Investigación. J.L. is grateful to ICREA environment for FTT reactions. 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STABILWAX PLOTU MS5A Molecule Ret. time (min) Molecule Ret. time (min) Molecule Ret. time (min) H2 CO 0.55 C 2 H4 0.68 H2 1.15 (CH3 )2 CO 0.65 C2 H6 0.75 N2 1.25 CH3 OH 0.70 CO 1.35 CH4 1.75 CH3 CH2 OH 2.10 CO2 2.00 Figures A.1 to A.15 show the chromatograms of each GC col- have different baselines levels, but each analysis has been car- umn for each sample analyzed and at each reference temperature. ried out with respect to the correspondent level, and therefore Table A.1 shows a guidance to the retention times used to assign there should not be any baseline effects in the computed product the detected peaks. We note that the different GC columns percentage. A160, page 8 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample A T = 200 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 250 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 300 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.1. Normalized chromatograms at 200, 250, and 300 ,◦ C for Sample A. A160, page 9 of 23 A&A 650, A160 (2021) Sample A T = 350 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 400 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 450 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.2. Normalized chromatograms at 350, 400, and 450 ◦ C for Sample A. A160, page 10 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample A T = 500 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 550 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 600 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Retention time (min) Fig. A.3. Normalized chromatograms at 500, 550, and 600 ◦ C for Sample A. A160, page 11 of 23 A&A 650, A160 (2021) Sample B T = 200 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 250 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 300 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.4. Normalized chromatograms at 200, 250, and 300 ◦ C for Sample B. A160, page 12 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample B T = 350 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 400 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 450 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.5. Normalized chromatograms at 350, 400, and 450 ◦ C for Sample B. A160, page 13 of 23 A&A 650, A160 (2021) Sample B T = 500 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 550 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 600 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Retention time (min) Fig. A.6. Normalized chromatograms at 500, 550, and 600 ◦ C for Sample B. A160, page 14 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample C T = 200 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 250 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 300 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.7. Normalized chromatograms at 200, 250, and 300 ◦ C for Sample C. A160, page 15 of 23 A&A 650, A160 (2021) Sample C T = 350 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 400 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 450 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.8. Normalized chromatograms at 350, 400, and 450 ◦ C for Sample C. A160, page 16 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample C T = 500 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 550 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 600 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Retention time (min) Fig. A.9. Normalized chromatograms at 500, 550, and 600 ◦ C for Sample C. A160, page 17 of 23 A&A 650, A160 (2021) Sample D T = 200 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 250 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 300 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.10. Normalized chromatograms at 200, 250, and 300 ◦ C for Sample D. A160, page 18 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample D T = 350 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 400 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 450 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.11. Normalized chromatograms at 350, 400, and 450 ◦ C for Sample D. A160, page 19 of 23 A&A 650, A160 (2021) Sample D T = 500 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 T = 550 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 a.u. 0.004 0.002 0.000 T = 600 °C 0.010 STABILWAX (O comp.) 0.008 PLOTU (hydrocarbons) MS5A (non-polar) 0.006 0.004 0.002 0.000 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Retention time (min) Fig. A.12. Normalized chromatograms at 500, 550, and 600 ◦ C for Sample D. A160, page 20 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample E T = 200 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 T = 250 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) a.u. 0.0 0.2 0.4 T = 300 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.13. Normalized chromatograms at 200, 250, and 300 ◦ C for Sample E. The plot shows only noise due to the lack of any reactant gas or product detected. A160, page 21 of 23 A&A 650, A160 (2021) Sample E T = 350 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 T = 400 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) a.u. 0.0 0.2 0.4 T = 450 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fig. A.14. Normalized chromatograms at 350, 400, and 450 ◦ C for Sample E. The plot shows only noise due to the lack of any reactant gas or product detected. A160, page 22 of 23 V. Cabedo et al.: FTT reactions in chondritic meteorites Sample E T = 500 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 T = 550 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) a.u. 0.0 0.2 0.4 T = 600 °C 0.4 STABILWAX (O comp.) PLOTU (hydrocarbons) 0.2 MS5A (non-polar) 0.0 0.2 0.4 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Retention time (min) Fig. A.15. Normalized chromatograms at 500, 550, and 600 ◦ C for Sample E. The plot shows only noise due to the lack of any reactant gas or product detected. A160, page 23 of 23