Variability of D and H in the Martian upper atmosphere observed with the MAVEN IUVS echelle channel

John T. Clarke (1) , Majd Mayyasi (1) , Dolon Bhattacharyya (1) , Nicholas M. Schneider (2) , William E. Mcclintock (2) , Justin I. Deighan (2) , A. Ian F. Stewart (2) , Jean-Yves Chaufray (3) , Michael S. Chaffin (2) , Sonal Kumar Jain (2) , Arnaud Stiepen (4) , Matteo Crismani (2) , Gregory M. Holsclaw (2) , Franck Montmessin (5) , Bruce M. Jakosky (2)

1 CSP - Center for Space Physics [Boston]
2 LASP - Laboratory for Atmospheric and Space Physics [Boulder]
3 HELIOS - LATMOS
4 LPAP - Laboratoire de Physique Atmosphérique et Planétaire
5 PLANETO - LATMOS

The MAVEN IUVS instrument contains an echelle spectrograph channel designed to measure D and H Ly α emissions from the upper atmosphere of Mars. This channel has successfully recorded both emissions, which are produced by resonant scattering of solar emission, over the course of most of a martian year. The fundamental purpose of these measurements is to understand the physical principles underlying the escape of H and D from the upper atmosphere into space, and thereby to relate present-day measurements of an enhanced HDO/H₂O ratio in the bulk atmosphere to the water escape history of Mars. Variations in these emissions independent of the solar flux reflect changes in the density and/or temperature of the species in the upper atmosphere. The MAVEN measurements show that the densities of both H and D vary by an order of magnitude over a martian year, and not always in synch with each other. This discovery has relevance to the processes by which H and D escape into space. One needs to understand the controlling factors to be able to extrapolate back in time to determine the water escape history from Mars at times when the atmosphere was thicker, when the solar flux and solar wind were stronger, etc. Further measurements will be able to identify the specific controlling factors for the large changes in H and D, which likely result in large changes in the escape fluxes of both species.

Domains: Sciences of the Universe [physics]; Astrophysics [astro-ph]; Earth and Planetary Astrophysics [astro-ph.EP]; Sciences of the Universe [physics]; Astrophysics [astro-ph]; Instrumentation and Methods for Astrophysic [astro-ph.IM]; Sciences of the Universe [physics]; Astrophysics [astro-ph]; Solar and Stellar Astrophysics [astro-ph.SR]

John T. Clarke, Majd Mayyasi, Dolon Bhattacharyya, Nicholas M. Schneider, William E. Mcclintock, et al.. Variability of D and H in the Martian upper atmosphere observed with the MAVEN IUVS echelle channel. Journal of Geophysical Research Space Physics, 2017, 122 (2), pp.2336-2344. ⟨10.1002/2016JA023479⟩. ⟨insu-01449485⟩