Radiation-driven Decomposition of Thiophene and Thiophene-derivatives within H2O-ice

Thiophene and several of its derivatives (2-methylthiophene, 3methylthiophene) have been detected on the surface of Mars in lacustrine mudstones using the pyrolysis-GC-MS instrument onboard NASA’s Curiosity Rover. The biosynthesis of thiophenes is considered an important production pathway on Earth, suggesting that thiophenes could serve as a secondary chemical biosignature on Mars. However, Mars lacks a global magnetic field allowing GCRs to readily penetrate the thin CO2 atmosphere and several meters into the regolith. GCRs can destroy the organic molecules present (i.e., chemical biosignatures). To date, the radiation-driven decomposition of these thiophenes has not been examined and their destruction rates constants have not been measured. Here, we provide radiolytic decomposition rates for thiophene as a neat ice and diluted in water ice to provide additional astrochemical context to the recent detections on Mars.