THE SEPTEMBER 2017 SOLAR ENERGETIC PARTICLE EVENT OBSERVEDBY MSL/RAD ON THE SURFACE OF MARS

The Radiation Assessment Detector (RAD) has been continuously monitoring the Martian surface radiation environment in Gale crater as part of NASA’s Mars Science Laboratory (MSL) mission since August 2012. On September 11 2017, RAD detected the strongest SEP event on the Martian surface to date. This event lead to the highest radiation levels since the beginning of the RAD operations in Gale crater. The SEPs associated with this solar storm increased the surface radiation dose by a factor of 3 over the course of a few hours, and the peak radiation dose was more than 50% higher than the previous maximum measured in October 2013.Here, we give an overview of the heliospheric conditions during the September 2017 solar storm, and present measurements of charged particle spectra during and before the event. RAD saw significant increases in the surface proton and helium fluxes, as well as in the neutral particles (neutrons and gamma-rays) created by interactions of the SEPs with the atmosphere and soil.