Details

Autor(en) / Beteiligte

• Zurek, R. W.
• Tolson, R. A.
• Bougher, S. W.
• Lugo, R. A.
• Baird, D. T.
• Bell, J. M.
• Jakosky, B. M.

Titel

Mars thermosphere as seen in MAVEN accelerometer data

Ist Teil von

• Journal of geophysical research. Space physics, 2017-03, Vol.122 (3), p.3798-3814

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2017

Quelle

Wiley-Blackwell Journals

Beschreibungen/Notizen

• The Mars thermosphere (above approximately 120 km) has been probed in situ for one Mars year using accelerometers on board the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. This region is affected by radiation and energy deposition from the Sun and by energy and momentum from the lower atmosphere. Densities derived from measurements made during the nominal science orbits (periapsis > 140 km) show consistent trends with solar zenith angle and Sun‐Mars distance, reflecting direct and indirect heating of the thermosphere, although orbit‐to‐orbit variability is still significant. The six Deep Dip campaigns that MAVEN has conducted (with periapsis dropping below ~135 km) significantly extend the vertical profiles of the densities derived from accelerometer data. These show complex structure and high variability, both dependent on season, local time, location, and lower atmosphere activity, including dust storms and wave propagation from a dynamic lower atmosphere. In particular, the terminators are a region of convoluted structure and high variability, which may be greatest in the postmidnight, predawn hours of the sol. This space‐time regime was not sampled by previous orbiters at Mars. While initial comparisons with thermospheric general circulation modes show broad areas of agreement, these terminator transition regions are not simulated well by current models. Judicious choice of the timing of these Deep Dip campaigns during the remaining MAVEN mission, as periapsis continues to precess through local time, latitude, and longitude in both hemispheres and in different seasons, should help clarify the processes at work in this complicated region. Key Points MAVEN accelerometer data fill major gaps in space‐time coverage of Mars in situ measurements of thermospheric bulk densities Comparisons with models revealed the largest differences in the lower thermosphere (120‐160 km) near the terminators, especially predawn Density variations are largest at the lowest (and coldest) altitudes, above the equator at midnight, and over the predawn midlatitudes