Science Seminars

Tracking Mars Hydrogen Loss from Surface Water to Upper Atmospheric H: Key Controls on H Loss Today and Throughout Time

Speaker: Michael Chaffin (LASP)
Date: Thursday, Nov 01, 2018
Time: 4:00 PM
Location: SPSC W120

Seminar Abstract:

H loss from the upper atmosphere of Mars has controlled the hydration and oxidation state of the planet over its history. Over the last four years, a convergence of spacecraft measurements has shown that this loss is seasonally variable and most likely controlled by lower to middle atmospheric conditions. In particular, the abundance of water above about 30 km altitude at concentrations near 100 ppm has been shown to be a key control on the abundance of upper atmospheric H and consequently H loss to space. These difficult-to-detect changes in middle atmospheric water produce ~10x changes in H escape on sub-seasonal timescales, and are sourced from small changes in middle atmospheric temperatures, possibly resulting from increased turbulence or dust abundances in the lower atmosphere. These newly acknowledged controls on H escape reveal that climate can be a key control on escape processes, a reversal of the canonical understanding of climate-escape coupling. Here I will present an overview of couplings between the lower and upper atmosphere relevant to H loss, identifying important constraints on H loss today from measurements and models and discussing potential difficulties in extrapolating the present situation throughout Mars history. In particular, I will focus on recent and near-term measurements from MAVEN, TGO, EMM, and other missions that have the potential to constrain our knowledge of key controls on H loss today and throughout time.