A Generalized Approach to Model the Spectra and Radiation Dose Rate of Solar Particle Events on the Surface of Mars

Abstract

For future human missions to Mars, it is important to study the surface radiation environment during extreme and elevated conditions. In the long term, it is mainly Galactic Cosmic Rays (GCRs) modulated by solar activity that contributes to the radiation on the surface of Mars, but intense solar energetic particle (SEP) events may induce acute health effects. Such events may enhance the radiation level significantly and should be detected as immediately as possible to prevent severe damage to humans and equipment. However, the energetic particle environment on the Martian surface is significantly different from that in deep space due to the influence of the Martian atmosphere. Depending on the intensity and shape of the original solar particle spectra as well as particle types, the surface spectra may induce entirely different radiation effects. In order to give immediate and accurate alerts while avoiding unnecessary ones, it is important to model and well understand the atmospheric effect on the incoming SEPs including both protons and helium ions. In this paper, we have developed a generalized approach to quickly model the surface response of any given incoming proton/helium ion spectra and have applied it to a set of historical large solar events thus providing insights into the possible variety of surface radiation environments that may be induced during SEP events. Based on the statistical study of more than 30 significant solar events, we have obtained an empirical model for estimating the surface dose rate directly from the intensities of a power-law SEP spectra.

Observations and Impacts of the 10 September 2017 Solar Events at Mars: An Overview and Synthesis of the Initial Results

“…The MARSIS instrument in particular has been making ionospheric sounding measurements of the Martian topside ionosphere, which can be used to infer the vertical electron density profiles of the topside ionosphere. During the SEP event period, MARSIS detected ionospheric echoes with unusually high peak electron densities (∼1–2 ×10 4 cm −3 ) at ∼120‐km altitudes in the deep nightside ionosphere, suggesting enhanced impact ionization by precipitating energetic particles (e.g., Guo, Zeitlin, et al, ; Norman et al, ; Withers, ). Associated with high SEP fluxes, MARSIS also observed the disappearance of ground reflection due to radio wave attenuation (i.e., radio blackout periods) by enhanced ionization below the peak density altitude of ∼100–150 km (Fowler et al, ; Girazian et al, ).…”

“…With no global magnetic field at Mars to deflect the charged particles nor a thick atmosphere to shield against them, SEPs with energies of 150 MeV/nuc and higher can penetrate down to the surface (Guo, Zeitlin, et al, ; Hassler et al, ). The detection of such an event at Mars is analogous to the ground‐level enhancement (GLE) event that occurs at Earth when ground‐based instruments detect secondary neutrons caused by high energy protons impacting the top of Earth's atmosphere.…”

Stellar proton event-induced surface radiation dose as a constraint on the habitability of terrestrial exoplanets

“…It has been extensively calibrated with a variety of experiments worldwide (Agostinelli et al 2003). The tool is also used in planetary sciences to model charged particle interactions with the atmosphere (Atri 2017;Guo et al 2018).…”

“…Space weather events, such as stellar flares, CMEs, and Stellar Proton Events (SPEs), abruptly bombard the planet with non-thermal radiation consisting of X-rays, EUV (XUV), and Stellar Energetic Particles (SEPs). Space weather has a significant impact on planets, with atmospheric effects such as erosion (Jakosky et al 2015), photochemical changes (Atri et al 2010;Segura et al 2010;Tabataba-Vakili et al 2016;Scheucher et al 2018), and enhanced radiation dose on the surface (Atri & Melott 2014;Atri 2017;Guo et al 2018). Earlier studies have shown that stellar flares have the capacity to significantly alter habitable conditions on planets (Airapetian et al 2017;Atri 2017;Lingam & Loeb 2017).…”

“…We extend our earlier work on the impact of SPEs on terrestrial exoplanets (Atri 2017) by incorporating data from 70 major SPEs and focus on the impact of spectral shape on the surface radiation dose. We calibrate our model with surface radiation dose observations on Mars (Lee et al 2018;Guo et al 2018) and compute SEP-induced radiation dose enhancement on exoplanetary surfaces.…”