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The Mars Topside Ionosphere Response to the X8.2 Solar Flare of 10 September 2017
Author(s) -
Thiemann E. M. B.,
Andersson L.,
Lillis R.,
Withers P.,
Xu S.,
Elrod M.,
Jain S.,
Pilinski M. D.,
Pawlowski D.,
Chamberlin P. C.,
Eparvier F. G.,
Benna M.,
Fowler C.,
Curry S.,
Peterson W. K.,
Deighan J.
Publication year - 2018
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2018gl077730
Subject(s) - mars exploration program , ionosphere , atmosphere of mars , flare , thermosphere , atmospheric sciences , orbiter , atmosphere (unit) , solar flare , environmental science , irradiance , physics , astrobiology , astronomy , meteorology , martian , optics
On 10 September 2017, irradiance from a magnitude X8.2 solar flare impacted Mars while the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiter was characterizing the Mars upper atmosphere. This solar flare was the largest to occur during the MAVEN mission to date, nearly tripling the ionizing irradiance impacting Mars in tens of minutes, and provides an opportunity to study the planet's response to extreme irradiance changes. This letter reports in situ observations of the Mars topside ionosphere's response to this flare above 155 km made 1.67 hr after the flare soft X‐ray peak. The observed plasma density increase is higher than expected based solely on increased ionization, and the electron temperature decreases below 225 km; both effects can be explained by an expanded neutral atmosphere, which efficiently dissipates any flare‐induced heating of the thermal electrons at altitudes where CO 2 is the dominant species. Further, the ion density and composition change significantly at both fixed altitude and pressure level, which can be explained by a change in the O:CO 2 density ratio, highlighting the importance this ratio has in determining ionospheric structure.