The Hayabusa2 spacecraft collected samples from the surface of the carbonaceous near-Earth asteroid (162173) Ryugu and brought them to Earth. The samples were expected to contain organic molecules, which record processes that occurred in the early Solar System. We analyzed organic molecules extracted from the Ryugu surface samples. We identified a variety of molecules containing the atoms CHNOS, formed by methylation, hydration, hydroxylation, and sulfurization reactions. Amino acids, aliphatic amines, carboxylic acids, polycyclic aromatic hydrocarbons, and nitrogen-heterocyclic compounds were detected, which had properties consistent with an abiotic origin. These compounds likely arose from an aqueous reaction on Ryugu’s parent body and are similar to the organics in Ivuna-type meteorites. These molecules can survive on the surfaces of asteroids and be transported throughout the Solar System.

The discovery of large (>100 u) molecules in Titan's upper atmosphere has heightened astrobiological interest in this unique satellite. In particular, complex organic aerosols produced in atmospheres containing C, N, O, and H, like that of Titan, could be a source of prebiotic molecules. In this work, aerosols produced in a Titan atmosphere simulation experiment with enhanced CO (N ₂ /CH ₄ /CO gas mixtures of 96.2%/2.0%/1.8% and 93.2%/5.0%/1.8%) were found to contain 18 molecules with molecular formulae that correspond to biological amino acids and nucleotide bases. Very high-resolution mass spectrometry of isotopically labeled samples confirmed that C ₄ H ₅ N ₃ O, C ₄ H ₄ N ₂ O ₂ , C ₅ H ₆ N ₂ O ₂ , C ₅ H ₅ N ₅ , and C ₆ H ₉ N ₃ O ₂ are produced by chemistry in the simulation chamber. Gas chromatography–mass spectrometry (GC-MS) analyses of the non-isotopic samples confirmed the presence of cytosine (C ₄ H ₅ N ₃ O), uracil (C ₅ H ₄ N ₂ O ₂ ), thymine (C ₅ H ₆ N ₂ O ₂ ), guanine (C ₅ H ₅ N ₅ O), glycine (C ₂ H ₅ NO ₂ ), and alanine (C ₃ H ₇ NO ₂ ). Adenine (C ₅ H ₅ N ₅ ) was detected by GC-MS in isotopically labeled samples. The remaining prebiotic molecules were detected in unlabeled samples only and may have been affected by contamination in the chamber. These results demonstrate that prebiotic molecules can be formed by the high-energy chemistry similar to that which occurs in planetary upper atmospheres and therefore identifies a new source of prebiotic material, potentially increasing the range of planets where life could begin. Key Words: Astrochemistry—Planetary atmospheres—Titan—Astrobiology. Astrobiology 12, 809–817.

We present a study of the formation and distribution of benzene (C₆H₆) on Titan. Analysis of the Cassini Mass Spectrometer (INMS) measurements of benzene densities on 12 Titan passes shows that the benzene signal exhibits an unusual time dependence, peaking ∼20 s after closest approach, rather than at closest approach. We show that this behavior can be explained by recombination of phenyl radicals (C₆H₅) with H atoms on the walls of the instrument and that the measured signal is a combination of (1) C₆H₆ from the atmosphere and (2) C₆H₆ formed within the instrument. In parallel, we investigate Titan benzene chemistry with a set of photochemical models. A model for the ionosphere predicts that the globally averaged production rate of benzene by ion‐molecule reactions is ∼10⁷ cm⁻² s⁻¹, of the same order of magnitude as the production rate by neutral reactions of ∼4 × 10⁶ cm⁻² s⁻¹. We show that benzene is quickly photolyzed in the thermosphere, and that C₆H₅ radicals, the main photodissociation products, are ∼3 times as abundant as benzene. This result is consistent with the phenyl/benzene ratio required to match the INMS observations. Loss of benzene occurs primarily through reaction of phenyl with other radicals, leading to the formation of complex aromatic species. These species, along with benzene, diffuse downward, eventually condensing near the tropopause. We find a total production rate of solid aromatics of ∼10⁻¹⁵ g cm⁻² s⁻¹, corresponding to an accumulated surface layer of ∼3 m.