The deuterium isotopic ratio of water released from the Martian caps as measured with TGO/NOMAD

GRL (2022) https://doi.org/10.1029/2022GL098161

Geronimo L. Villanueva, Giuliano Liuzzi, Shohei Aoki, Shane W. Stone, Adrian Brines, Ian R. Thomas, Miguel Angel Lopez-Valverde, Loic Trompet, Justin Erwin, Frank Daerden, Bojan Ristic, Michael D. Smith, Michael J. Mumma, Sara Faggi, Vincent Kofman, Séverine Robert, Lori Neary, Manish Patel, Giancarlo Bellucci, J.-J. Lopez-Moreno, Ann Carine Vandaele

We report vertical profiles of water and D/H for one Martian year as measured with the TGO/NOMAD instrument. The observations were performed via solar occultation, providing water profiles up to ∼100 km and D/H up to ∼60 km, with a vertical resolution of 1–2 km. The measurements reveal dramatic variability of water and D/H over short timescales and with altitude and location on the planet. We investigated the release of seasonal water from the polar caps during southern and northern summer, by mapping water and its D/H near the polar regions. Above the hygropause, the D/H drops substantially below 2 VSMOW, and both seasonal polar caps show a consistent and enriched D/H of 5–7 VSMOW within the hygrosphere.

villanueva22 hdo

Seasonal evolution of water and its D/H across a full Martian Year, starting on MY34 and ending on LS=240 MY35. Only H2O values with uncertainties lower than 15 ppmv and D/H values with sigma lower than 1VSMOW are shown. The global dust storm and the large regional dust storm that took place during LS=190 to LS=360 of MY34 greatly modified the atmosphere, and brought water to very high altitudes. In all cases, the D/H drops notably beyond the hygropause to 1-2 VSMOW, and the profiles show an enriched value of 5-7 VSMOW within the hygrosphere. The hygrosphere can be challenging to properly sample, since in many cases it extends only to altitudes less than 20 km and is close to the detection limit via occultation. The latitude sub-panels indicate the sampled latitudes during that season and the colors indicate average value for that season.