Density Fluctuations in the Lower Thermosphere of Mars Retrieved From the ExoMars Trace Gas Orbiter (TGO) Aerobraking

David Jesch,Paul Hartogh,Francesco Castellini,Erdal Yiğit,Alexander S Medvedev

doi:10.3390/atmos10100620

David Jesch, Paul Hartogh + Show 3 more

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https://doi.org/10.3390/atmos10100620

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Abstract

The upper atmosphere of Mars is constantly perturbed by small-scale gravity waves propagating from below. As gravity waves strongly affect the large-scale dynamics and thermal state, constraining their statistical characteristics is of great importance for modeling the atmospheric circulation. We present a new data set of density perturbation amplitudes derived from accelerometer measurements during aerobraking of the European Space Agency’s Trace Gas Orbiter. The obtained data set presents features found by three previous orbiters: the lower thermosphere polar warming in the winter hemisphere, and the lack of links between gravity wave activity and topography. In addition, the orbits allowed for demonstrating a very weak diurnal variability in wave activity at high latitudes of the southern winter hemisphere for the first time. The estimated vertical damping rates of gravity waves agree well with theoretical predictions. No clear anticorrelation between perturbation amplitudes and the background temperature has been found. This indicates differences in dissipation mechanisms of gravity waves in the lower and upper thermosphere.

Highlights

The Trace Gas Orbiter (TGO), launched on 14 March 2016, is the first mission of the European SpaceAgency’s (ESA’s) ExoMars program, with the primary objective to search for the evidence of methane and other trace gases
TGO is the fourth spacecraft that was put through an extensive aerobraking campaign in the Martian atmosphere following Mars Global Surveyor (MGS) [30,31,32], Mars Odyssey (ODY) [33,34,35,36], and Mars Reconnaissance Orbiter (MRO) [37,38,39,40,41]
This paper has presented an analysis of gravity waves (GWs)-like disturbances of density fluctuations in aerobraking measurements by European SpaceAgency (ESA’s) TGO mission

Summary

Introduction

The Trace Gas Orbiter (TGO), launched on 14 March 2016, is the first mission of the European SpaceAgency’s (ESA’s) ExoMars program, with the primary objective to search for the evidence of methane and other trace gases. TGO performed an 11-month-long aerobraking campaign between 14 March 2017 and 20 February 2018 to gradually reduce its orbital period from approximately 24 h to 2 h, by passing through the Martian atmosphere times at the pericenters of the initially highly elliptical orbit, thereby accumulating a total drag ∆V of about 1017 m s−1 with a limited propellant usage. Our work exploits the fact that TGO reached the denser layers in the thermosphere and the on-board accelerometers registered variations of the atmospheric drag with high temporal and spatial resolution. This allowed for determining small-scale thermospheric density fluctuations associated with gravity waves (GWs)

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