My graduate research at Boston University is centered around understanding how the upper atmosphere of Mars responds to the large and sudden influxes of energy from solar flares.
- Why study solar flare effects at Mars?
Solar flares are useful events from which to examine how the solar irradiance (photons) constantly being emitted from the Sun regulate the atmospheric conditions at Mars, and how the Martian atmosphere has evolved over solar system history.
Because it takes time for the atmosphere to dissipate the great amounts of energy rapidly provided by a solar flare, we can measure and infer the atmosphere’s underlying processes, such as thermal expansion and chemical changes, as they return the atmosphere to equilibrium following a solar flare. The upper atmosphere of Mars is significantly influenced by these large and sudden changes, which alter its altitude-dependent neutral and ion densities and composition – affecting rates of atmospheric escape. Because amounts of solar irradiance and solar activity were greater in early solar system history, investigating solar flare effects can inform how solar flares may have cumulatively influenced the loss of Mars’ denser ancient atmosphere. More broadly, the response of the atmosphere of Mars to a solar flare can be compared with flare event simulations and the response of other planetary atmospheres to solar flares in order to better understand how the Sun and other stars shape planetary environments and their evolution.
Early and present day Mars (NASA visualization adaptation)
To characterize the effects of solar flares on the upper atmosphere of Mars, I use a combination of observations and simulations and make comparisons between flare-affected and typical, baseline atmospheric conditions. The conditions I investigate are:
- density and composition, for both neutral and ions species (thermosphere, ionosphere)
- changes with altitude, especially at higher altitudes (> 150 km) where flare effects have been less studied
- changes with time, since solar flare energy can continue affecting the atmosphere for as long as multiple hours
- sources of change (e.g. changes in the amounts of arriving energetic solar flare irradiance, chemical changes, thermal expansion of the upper atmosphere due to the flare)
I began this research with observational analyses, using measurements from the mass spectrometer instrument (NGIMS) on the MAVEN spacecraft in orbit at Mars to investigate an in-situ snapshot of the atmosphere’s conditions roughly 90 minutes after the impact of a large solar flare on September 10, 2017.
Currently, I am investigating time-dependent simulations of the atmosphere’s conditions during this same solar flare event from the M-GITM global circulation model to characterize their changes over a longer extent of time, before and after the MAVEN observations were made.
My conference abstracts and papers are available on ADS here. A paper presenting results from examining the Martian ionosphere’s observed changes during the 9/10/2017 solar flare event from the context of the thermosphere’s thermal expansion (Cramer and Withers, 2023) has been recently added!
Descriptions of my earlier research are provided in my CV!
image credits: NASA GSFC