# # Program information file # PROGRAM_ID 2024B018 PROGRAM_TITLE Mapping the 13C/12C ratio in Martian CO2: a search for fractionation effects in the near-surface atmosphere PROGRAM_INV1 Juan Alday PROGRAM_INV2 Shohei Aoki PROGRAM_INV3 Thomas K. Greathouse PROGRAM_INV4 Therese Encrenaz PROGRAM_INV5 Manish Patel PROGRAM_SCICAT major planets / satellites PROGRAM_ABSTRACT_BEG The 13C/12C isotopic ratio in CO2 provides important information about the evolution of the Martian climate. In particular, this ratio carries the imprints from long-term processes that have shaped the C reservoir on Mars and, when coupled with climate evolution models, can help us reconstruct the partial pressure of CO2 in the past, when Mars is thought to have been much more habitable than it is today. In situ measurements by the Curiosity Rover revealed an enrichment of 13C/12C in Martian CO2 with respect to Earth, suggesting that a substantial fraction of the C reservoir has escaped to space. However, while these measurements are generally taken as representative of the present-day 13C/12C in the bulk atmosphere, this enrichment has not been validated by any other means, including other in situ measurements and ground-based observations, which suggest instead a lower or non-existent enrichment of 13C/12C with respect to Earth. While the non-consistency of the values derived from different techniques might just be caused by systematic errors, the observed variability in the measurements might nonetheless reveal real fractionation of the 13C/12C ratio in the near-surface atmosphere of Mars. We propose to perform the first global mapping of 13C/12C in Martian CO2 with IRTF/TEXES to search for spatial and diurnal variability and identify the existence of processes that produce fractionation of 13C/12C in the near-surface Martian atmosphere. In order to simultaneously measure the abundance of [12C]O2 and [13C]O2 on Mars, we use the high spectral resolution mode of TEXES [R~80,000] in a spectral range between 920-926 cm-1, which allows us to resolve the absorption lines of both isotopologues. By performing sequential scans over the Mars disk during 7.5 hours in January 2025, we will create two global maps of 13C/12C centered at different longitudes. PROGRAM_ABSTRACT_END