It is still unknown how much water has escaped from Mars during its history. Hydrogen escape from Mars's atmosphere probably played a major role in drying the planet, but present-day Hloss rates (about 3x10^26 atoms per second on average) cannot explain the geological evidence for the large volumes of liquid water on ancient Mars. Here we used the three-dimensional Mars-Planetary Climate Model to show that H loss rates could have increased by more than one order of magnitude (6x10^27 atoms per second) during higher spin axis obliquity periods, notably in the last few million years when Mars's obliquity was about 35 deg on average. The resulting accumulated H escape over Mars's history translates into an approx. 80 m global equivalent layer, which is close to the lower limit of geological estimates, assessing the major role of atmospheric escape in drying Mars.
@article{arxiv.2505.16692,
title = {Increased hydrogen escape from Mars atmosphere during periods of high obliquity},
author = {Gabriella Gilli and Francisco González-Galindo and Jean-Yves Chaufray and Ehouarn Millour and François Forget and Franck Montmessin and Franck Lefèvre and Joseph Naar and Yangcheng Luo and Margaux Vals and Loïc Rossi and Miguel Ángel López-Valverde and Adrián Brines},
journal= {arXiv preprint arXiv:2505.16692},
year = {2025}
}