Martian water loss to space enhanced by regional dust storms

Abstract

Mars has lost most of its initial water to space as atomic hydrogen and oxygen 1,2 . Spacecraft measurements have determined that the hydrogen component of this loss undergoes large variations with season 3-6 inconsistent with longstanding explanations 7,8 . The cause is incompletely understood, with likely contributions from seasonal changes in atmospheric circulation, dust activity, and solar extreme ultraviolet input. While some modeling and indirect observational evidence suggest dust activity can explain the seasonal trend [9][10][11][12][13][14][15] , no prior study has been able to unambiguously distinguish seasonal from dust-driven forcing. Here we present synoptic measurements of dust, temperature, ice, water, and hydrogen on Mars during a regional dust event, demonstrating that individual dust events can boost planetary H loss by a factor of 5-10. This regional storm occurred in the declining phase of the known seasonal trend, establishing that dust forcing can override this trend to drive enhanced escape. Because similar regional storms occur in most Mars years 16 , these storms may be responsible for a large fraction of Martian water loss, with implications for Mars atmospheric evolution and planetary habitability in general.

Explaining NOMAD D/H Observations by Cloud‐Induced Fractionation of Water Vapor on Mars

“…This will then link the observations by NOMAD (and ACS) to the upper atmospheric data gathered by instruments on MAVEN (Chaffin et al, 2017(Chaffin et al, , 2021Stone et al, 2020). Eventually, a full story about water on Mars and its escape to space on the short (annual) and long timescales can be constructed.…”

Reappraising the Production and Transfer of Hydrogen Atoms From the Middle to the Upper Atmosphere of Mars at Times of Elevated Water Vapor

“…It is to be noted that a large part of the MY34 C-storm was not monitored by ACS due to TGO's orbit constraints. The data gap actually covers the peak activity of this regional storm, which implies our results would have underestimated the MY34 C-storm upward flux, since its water vapor profile exhibits distinctly smaller abundances compared to other cases (not shown) Yet, this event produced an intense brightening of the hydrogen corona (Chaffin et al, 2021). Instead, we chose to apply our model to the C-storm that occurred in MY35 that was consistently observed by ACS, which featured similar timing and strength ) in the parcel.…”

The Emirates Mars Mission

“…Perhaps the most dramatic influence of the lower atmosphere on the upper is the increase in H concentration and escape rate induced by dust activity. While the exact mechanisms of the enhancement are not known, H escape is greatly enhanced with season (Chaffin et al 2014;Clarke et al 2014;Bhattacharyya et al 2015;Halekas 2017), and H loss strongly responds to some regional dust storms (Chaffin et al 2021). The enhancement is thought to be related to increased water concentrations at altitudes greater than 20 km, which are enabled by higher atmospheric temperatures resulting from dust heating (Maltagliati et al 2011(Maltagliati et al , 2013Fedorova et al 2018;Heavens et al 2018;Aoki et al 2019;Fedorova et al 2020).…”