HAO Colloquium - Robert Marshall, CU Boulder

X-ray Imaging of Energetic Particle Precipitation from the Radiation Belts: The AEPEX CubeSat Mission

Radiation belt electron fluxes can be enhanced by two order of magnitude or more during geomagnetic storms; subsequently, these fluxes decay back to nominal levels over the course of days to weeks. However, the mechanisms by which this enhancement and decay occurs are not well understood. Precipitation into the upper atmosphere is one of the primary loss mechanisms for radiation belt electrons, particularly during the decay phase. When these particles impact the upper atmosphere, they create new ionization in the mesosphere and lower thermosphere, which leads to a chemical response that increases NOx and HOx and destroys ozone. Quantifying both the loss from the radiation belts and the impact on the atmosphere requires an accurate estimate of the flux, energy spectrum, and spatial and temporal scales of this electron precipitation. However, such assessments are particularly difficult due to limitations and uncertainties of most measurement techniques. 

The Atmospheric Effects of Precipitation through Energetic X-rays (AEPEX) CubeSat mission is designed to quantify these parameters of radiation belt precipitation by measuring the bremsstrahlung X-rays created during the precipitation process. Hard X-rays from electron precipitation have previously been measured from high-altitude balloons and satellites, but have never been imaged from space, providing the spatial resolution needed to assess large-scale and global impacts. AEPEX will image the X-ray fluxes produced by the atmosphere, providing measurements of spatial scales, along with the X-ray flux and spectrum. A solid-state energetic particle detector will measure the precipitating electron energy spectrum, which is used to constrain the inversion of X-ray fluxes to electron fluxes. Simulation work has been conducted to show that the combined particle and X-ray measurements can be used to accurately measure the precipitating electron flux and the atmospheric ionization response. In this talk, I will provide an overview of the science goals of the AEPEX mission, a description of the inversion process by which we estimate the electron precipitation flux, and a detailed description of the instrument, spacecraft, and mission design. AEPEX is currently in the design phase, and the mission is expected to launch in mid-2022. 

Date and time: 
Wednesday, November 4, 2020 - 2:00pm to 3:00pm