Seasonal variation of Martian pick-up ions: Evidence of breathing exosphere. (15th December 2015)

• Record Type: Journal Article
• Authors: Yamauchi, M.; Hara, T.; Lundin, R.; Dubinin, E.; Fedorov, A.; Sauvaud, J.-A.; Frahm, R.A.; Ramstad, R.; Futaana, Y.; Holmstrom, M.; Barabash, S.
• Is Part Of: Planetary and space science. Volume 119(2015)
• Page Start: 54
• Page End: 61
• Publication Date: 2015-12-15
• Subjects: Pick-up ions -- Mars Express -- Exosphere -- Hydrogen corona -- Solar UV effect -- Seasonal variation -- Solar cycle -- Atmospheric escape -- ASPERA-3; Space sciences -- Periodicals; Atmosphere, Upper -- Periodicals; Sciences spatiales -- Périodiques; Haute atmosphère -- Périodiques; 523
• DOI: 10.1016/j.pss.2015.09.013
• Languages: English
• ISSNs: 0032-0633

Abstract

Abstract: The Mars Express (MEX) Ion Mass Analyser (IMA) found that the detection rate of the ring-like distribution of protons in the solar wind outside of the bow shock to be quite different between Mars orbital summer (around perihelion) and orbital winter (around aphelion) for four Martian years, while the north–south asymmetry is much smaller than the perihelion–aphelion difference. Further analyses using eight years of MEX/IMA solar wind data between 2005 and 2012 has revealed that the detection frequency of the pick-up ions originating from newly ionized exospheric hydrogen with certain flux strongly correlates with the Sun–Mars distance, which changes approximately every two years. Variation due to the solar cycle phase is not distinguishable partly because this effect is masked by the seasonal variation under the MEX capability of plasma measurements. This finding indicates that the variation in solar UV has a major effect on the formation of the pick-up ions, but this is not the only controlling factor. Highlights: First time statistics of pick-up ions upstream of the Martian bow shock. First time examination of solar-cycle variation of pick-up ions at any planet. Unexpectedly strong perihelion–aphelion difference in pick-up ions detection. Solar UV is major but not the only controlling factor to ionize exospheric hydrogen. Variation due to the solar cycle phase is not distinguishable.