Energetic particles detected by the Electron Reflectometer instrument on the Mars Global Surveyor, 1999–2006

Abstract

[1] We report the observation of galactic cosmic rays and solar energetic particles by the Electron Reflectometer instrument aboard the Mars Global Surveyor (MGS) spacecraft from May of 1999 to the mission conclusion in November 2006. Originally designed to detect low-energy electrons, the Electron Reflectometer also measured particles with energies >30 MeV that penetrated the aluminum housing of the instrument and were detected directly by microchannel plates in the instrument interior. Using a combination of theoretical and experimental results, we show how the Electron Reflectometer microchannel plates recorded high energy galactic cosmic rays with $45% efficiency. Comparisons of this data to galactic cosmic ray proton fluxes obtained from the Advanced Composition Explorer yield agreement to within 10% and reveal the expected solar cycle modulation as well as shorter timescale variations. Solar energetic particles were detected by the same mechanism as galactic cosmic rays; however, their flux levels are far more uncertain due to shielding effects and the energy-dependent response of the microchannel plates. Using the solar energetic particle data, we have developed a catalog of energetic particle events at Mars associated with solar flares and coronal mass ejections, which includes the identification of interplanetary shocks. MGS observations of energetic particles at varying geometries between the Earth and Mars that include shocks produced by halo, limb, and backsided events provide a unique data set for use by the heliophysics modeling community.

The September 2017 SEP Event in Context With the Current Solar Cycle: Mars Express ASPERA‐3/IMA and MAVEN/SEP Observations

“…Nevertheless, IMA appears sensitive to energetic >20 MeV protons and MeV electrons as both are expected to generate the counts measured in FTO bins 10–12, electrons dominating in bins 6–9, and only protons registering in bins 13–14. A lower limit ∼20 MeV for penetrating protons is consistent with the ∼30 MeV lower energy limit for energetic particles triggering background counts in the MGS/ER instrument found by Delory et al (). Limits near these values are expected as required to penetrate the typical aluminum housings of electrostatic plasma analyzers.…”

Variability of Precipitating Ion Fluxes During the September 2017 Event at Mars

“…High‐energy particles (>~2‐MeV electrons and ~20‐MeV protons) can induce false counts on ion and electron spectrometers (Frahm et al, ) equivalent to an energy‐independent signal (Delory et al, ). During the solar event between 11 and 23 September 2017, SEPs induced a significant background in SWIA measurements for several days with a count rate peak of equivalent to an energy differential flux of which occurred on 12 September.…”

Investigation of Mars' ionospheric response to solar energetic particle events

“…Therefore a flat spectrum from 10 to 20 keV channels indicates penetrating particles (>30 MeV) while any detectable slope shows a contribution from 10 to 20 keV electrons. Using this method, a total of 85 discrete events recorded by MGS/ER can be reasonably attributed to the presence of particle fluxes that penetrate the detector housing (>30 MeV) between May of 1999 and November of 2006 (for details of the ER response to high‐energy particles and detection of the penetrating particles as well as the data set of varying solar events recorded by the ER at Mars, see Brain et al [2012] and Delory et al [2012]). Of these 85 SEP events, 41 were found to be temporally correlated with the CMEs detected by Large Angle and Spectrometric Coronagraph Experiment (LASCO) on the Solar and Heliospheric Observatory (SOHO) (for the list of these events, see Delory et al [2012, Table 1]).…”

“…Of the 85 SEP events identified using ER data, we identify 6 periods for which radio science profiles were also available. These 6 periods are also listed among the SEP events which are linked with specific CMEs detected by the Large Angle and Spectrometric Coronagraph on board the Solar and Heliospheric Observatory (LASCO) instrument on SOHO by Falkenberg et al [2011, Table 1] and Delory et al [2012, Table 1]. Table 1summarizes these time periods and associated information about the SEPs and electron profiles recorded during these times.…”