Energy Input of EUV, Solar Wind, and SEPs at Mars: MAVEN Observations During Solar Minimum

Abstract

AbstractSolar extreme ultraviolet (EUV) radiation, the solar wind, and solar energetic particles (SEPs) are variable sources of ionization and heating to the Martian atmosphere. Mars Atmosphere Volatile Evolution’s (MAVEN's) elliptical orbit provides a means to characterize these solar drivers immediately upstream of Mars. We have calculated the energy fluxes of EUV, solar wind, and SEPs while MAVEN is outside of the Martian induced magnetosphere. By time‐averaging observations over 2–5 month periods, we reduced short‐term variability to resolve seasonal and solar cycle trends. For the duration spanning the declining phase of solar cycle 24 and three Mars years, the calculated energy fluxes in units of 109 eV/cm2/s were 650–1,400 for EUV, 77–180 for solar wind ions, 2.4–7.4 for solar wind electrons, 0.01–2.7 for SEP ions, and 0–0.4 for SEP electrons. We estimated the fraction of these energy fluxes that would reach the atmosphere and determined that precipitating particle fluxes on the dayside would need to exceed 1012 eV/cm2/s to compare to EUV. We also predicted that SEPs may impart as much or more energy flux than solar wind electrons on the nightside during periods of strong and weak coronal mass ejection activity. We then discussed and decoupled seasonal variation from the solar drivers to reveal trends and outliers as a function of solar cycle. Finally, we compared MAVEN observations during a weak solar cycle to prior estimates of EUV, solar wind, and SEPs from the young sun, and identified times when MAVEN‐observed peak energy fluxes were close to the steady‐state energy fluxes of the ancient solar system.