An Empirical Predictive Model for Atmospheric H Lyman-a Emission
Brightness at Mars
Abstract
Characterizing the abundance of atmospheric hydrogen (H) at Mars is
critical for determining the current and, subsequently, the primordial
water content on the planet. At present, the atmospheric abundance of
Martian H is not directly measured but is simulated using proprietary
models that are constrained with observations of H Lyman-a emission
brightness, as well as with observations of other atmospheric
parameters, such as temperature and solar UV irradiance. To make the
data needed to model H abundances and escape rates more accessible to
the community, this work utilizes over nine years of observations of H
Lyman-a emissions made with the Mars Atmosphere and Volatile Evolution
(MAVEN) mission. The H brightness in the upper atmosphere of Mars is
analyzed for statistical variability across multiple variables and found
to be dependent on solar illumination, solar cycle, and season. The
resulting data trends are used to derive empirical fits to build a
predictive framework for future observations or an extrapolative tool
for primordial estimates. Data that was intentionally not included in
the empirical derivations are used to validate the predictions and found
to reproduce the H Lyman-a brightness to within 18% accuracy, on
average. This first of its kind predictive model for H brightness is
presented to the community and can be used with atmospheric models to
further derive and interpret the abundances and escape rate of H atoms
at Mars.