Reappraising The Production And Transfer Of Hydrogen
To The Upper Atmosphere At Times Of Elevated Water
Vapor
F. Montmessin, Latmos/Ipsl, Uvsq Université Paris-Saclay, Sorbonne Université, Cnrs, Guyancourt, France, D. A.
Belyaev, Space Research Institute Of The Russian Academy Of Sciences (Iki Ras), Moscow, Russia, F. Lefèvre, Latmos,
Sorbonne Univ. Paris France, J. Alday, Open University, Milton Keynes, U.K., M. Vals, Latmos, Guyancourt, A. A. Fedorova, O. I. Korablev, A. V. Trokhimovskiy, Iki Moscow, M. S. Chaffin, N. M. Schneider, Lasp, Boulder, Colorado,
United States

Introduction: Water Escape On Mars Has Recently Undergone A Paradigm Shift With The Discovery Of
Unexpected Seasonal Variations In The Population Of
Hydrogen Atoms In The Exosphere Where Thermal Escape Occurs And Results In Water Lost To Space. This
Discovery Led To The Hypothesis That, Contradicting
The Accepted Pathway, Atomic Hydrogen In The Exosphere Was Not Only Produced By Molecular Hydrogen But Mostly By High Altitude Water Vapor. Enhanced Presence Of Water At High Altitude During
Southern Spring And Summer, Due To Atmospheric
Warming And Intensified Transport, Favors Production
Of H Through Photon-Induced Ion Chemistry Of Water
Molecules And Thus Appears To Be The Main Cause Of
The Observed Seasonal Variability In Escaping Hydrogen (Chaffin Et Al., 2014; 2017; Clarke Et Al., 2014,
Heavens Et Al., 2018). This Hypothesis Is Supported
By The Large Concentrations Of Water Vapor Observed