Changes in the thermosphere and ionosphere of Mars from Viking to MAVEN. Issue 21 (5th November 2015)

• Record Type: Journal Article
• Authors: Withers, Paul; Vogt, Marissa; Mahaffy, Paul; Benna, Mehdi; Elrod, Meredith; Jakosky, Bruce
• Is Part Of: Geophysical research letters. Volume 42:Issue 21(2015:Nov.)
• Page Start: 9071
• Page End: 9079
• Publication Date: 2015-11-05
• Subjects: Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1002/2015GL065985
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: We compare Viking and Mars Atmosphere and Volatile EvolutioN mission (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) observations of the thermosphere and ionosphere of Mars in order to test predictions of large variations in conditions over the solar cycle and with season. Substantial differences exist between the Viking observations at solar minimum and near aphelion and the MAVEN NGIMS observations at moderate solar activity and near perihelion. Differences in the O/CO2 ratio, the O + ionospheric peak, ion densities at high altitude, and neutral and ion scale heights can be attributed to differences in solar activity and season, but the relative importance of solar activity and season for these differences was not established. Current models do not explain the observed differences in the mixing ratios of N, NO, and O2 . These results place new constraints on models of how the thermosphere and ionosphere of Mars vary over the solar cycle and with season. Key Points: Vertical structure of the thermosphere above 250 km differs significantly from expectations Exobase altitude differs greatly from Viking to MAVEN Gross chemical composition similar from Viking to MAVEN