P049-06
O2+ temperature profiles measured by MAVEN STATIC

Friday, 11 December 2020: 05:55
Virtual
Kathleen Gwen Hanley1, David L Mitchell1, James P McFadden2, Christopher M Fowler3, Shane Stone4, Roger V Yelle4, Marcin Pilinski5, Mehdi Benna6, Meredith K Elrod6, Laila Andersson7, Robert Ergun5 and Bruce Martin Jakosky8, (1)Space Sciences Laboratory, University of California Berkeley, Berkeley, CA, United States, (2)Univ California Berkeley, Berkeley, CA, United States, (3)Univ Colorado, Boulder, CO, United States, (4)University of Arizona, Lunar and Planetary Laboratory, Tucson, AZ, United States, (5)Laboratory for Atmospheric and Space Physics, Boulder, CO, United States, (6)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (7)Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, United States, (8)University of Colorado Boulder, Boulder, CO, UNITED STATES
Recorded Presentation
Abstract:
Ion temperature is a key parameter that controls the structure of planetary ionospheres, and at Mars, the ability of planetary ions near the exobase to escape to space. In this study, we use data collected by the Mars Atmosphere and Volatile EvolutioN (MAVEN) SupraThermal And Thermal Ion Composition (STATIC) instrument to present the first measurements of ion temperature at Mars since the Viking landers of the 1970s.

We present O2+ temperature profiles measured in Mars’ ionosphere when MAVEN’s periapsis occurred close to local noon, midnight, dawn, and dusk. Ion temperatures are cold enough that corrections to the instrument’s energy-angle response function are essential. This and other instrumental effects make deriving reliable ion temperatures from STATIC data challenging. Three different methods are used to calculate O2+ temperatures using different assumptions which are valid over overlapping altitude ranges. Selection of the best method is based on the measured distribution's width in energy and angle. O2+ temperatures are compared with neutral Ar temperatures measured by the Neutral Gas and Ion Mass Spectrometer and electron temperatures from the Langmuir Probe and Waves experiment, both aboard MAVEN.

Ion and neutral temperatures are expected to converge from the exobase (~200 km) to ~150 km, because of thermalization with atmospheric neutrals. However, we find that temperature differences between Ar and O2+ persist down to MAVEN’s periapsis of 150 km for some solar zenith angles. The electron temperature is higher than the ion temperature in this altitude range. We also note lower temperatures and more variability on the nightside than the dayside, which is unsurprising due to the patchy nature of the nightside ionosphere.

Substantial progress has been made toward deriving reliable ion temperatures from STATIC from periapsis to >1000 km altitude. Once the necessary corrections are finalized, O2+ temperatures will be calculated for nearly the entire MAVEN mission, providing a new tool for systematically analyzing the Martian atmosphere.

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