Solar Energetic Particles at Mars

Jolitz, Rebecca Dawn

Graduate Thesis Or Dissertation

Solar Energetic Particles at Mars Public Deposited

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Citeable URL: https://scholar.colorado.edu/concern/graduate_thesis_or_dissertations/nk322f44h

Abstract

Solar energetic particles (SEPs) are both a hazard to human spaceflight and a source of energy to planetary atmospheres. Since Mars lacks a global magnetic field, Mars may be more susceptible to this type of radiation than Earth. This thesis investigates the precipitation of SEPs at Mars via a combination of model predictions and observation.First, a 3-D Monte Carlo test particle and energy degradation simulation called ASPEN (Atmospheric Scattering of Protons, Electrons, and Neutrals) was developed to describe SEP transport in inhomogeneous magnetic fields and precipitation into an atmosphere. ASPEN was applied to predict ionization above Martian crustal fields, finding that crustal fields attenuated the low-energy range of the spectra measured at the peak of the 2003 “Halloween” SEP event.Next, ASPEN was used to study the transport of 10-200 keV electrons in the near Mars environment, from the solar wind to atmospheric entry. While precipitation was predicted to be favored into magnetic cusps, the simulation predicted a fraction of energetic electrons can enter closed field regions. This is because the particles are affected by non-adiabatic mechanisms as well as curvature and gradient drifts, which are proportional to particle energy.Finally, the total energy flux incident on Mars from EUV, solar wind, and SEPs was calculated using MAVEN spacecraft data during the declining solar cycle. On average, the energy flux from extreme ultraviolet radiation (EUV) exceeded that of solar wind, and solar wind energy flux exceeded SEP energy flux. Solar wind ion energy flux could sporadically become comparable to EUV energy flux, but not exceed it by a margin sufficient to displace EUV as the dominant source of the dayside ionosphere. On the other hand, SEP ions did reach an intensity comparable to solar wind electrons and are possibly sufficient to increase nightside ionization. These observations were contextualized with seasonal and solar cycle variation, and compared to predictions of energy fluxes at ancient Mars.

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