REAL: A CubeSat to Study Energetic Electron Precipitation into Earth`s Atmosphere

Robyn Millan ¹ Thomas Sotirelis ² John Sample ³ Leslie Woodger ¹ Wen Li ⁴ Romina Nikoukar ² Sasha Ukhorskiy ² Arlo Johnson ³ Mykhalo Shumko ³ Luisa Capannolo ⁴

¹Physics and Astronomy, Dartmouth College, Hanover, NH, USA
²Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA
³Physics, Montana State University, Bozeman, MT, USA
⁴Astronomy, Boston University, Boston, MA, USA

The REAL (Relativistic Electron Atmospheric Loss) CubeSat will characterize different modes of atmospheric electron precipitation by making high time resolution measurements of precipitating electron pitch angle and energy distributions. Although significant progress has been made in identifying plasma waves that drive energetic electron precipitation (EEP) [e.g., Thorne, 2010 for review], there are missing links in our understanding, including the physical “modes” of wave-particle interactions. For example, electrons may be scattered slowly through a diffusive process [e.g., Shprits et al., 2008 review], or rapidly through nonlinear processes [e.g., Albert, 2000; Bortnik et al., 2008, Omura et al., 2015]. The physical mode determines the scattering rate and thus the impact on Earth`s radiation belts. REAL will distinguish between these modes of precipitation by measuring the pitch angle distribution of electrons over a wide energy range, from keV to MeV, in a low Earth orbit (LEO), and with time resolution sufficient to resolve electron microbursts. LEO is ideal for measuring precipitation since the atmospheric loss cone is larger (~60 deg) than at the equator (few degrees). The pitch angle-resolved measurements will also distinguish between precipitating, quasi-trapped, and trapped populations, thus more accurately quantifying the electron loss rate and the impact on Earth`s atmosphere.