In-situ study of comet 1P/Halley during its 1986 apparition revealed a surprising abundance of organic coma species. High-resolution mass-spectrometric data collected at comet 67P/Churyumov-Gerasimenko by ESA's Rosetta mission unveil the chemical structure of complex cometary organics. An ensemble of individual molecules with masses up to 140 Da is identified, inconsistent with significant polymeric matter. The ensemble's average composition (C₁H₁.₅₆O₀.₁₃₄N₀.₀₄₆S₀.₀₁₇) resembles meteoritic soluble organic matter and includes chain-based, cyclic, and aromatic hydrocarbons (6:3:1 ratio). Its properties (except H/C ratio) resemble other Solar System organics, suggesting a shared prestellar history.

N. Hänni, K. Altwegg, M. Combi, S. A. Fuselier, J. De Keyser, M. Rubin, S. F. Wampfler