SH31A-2393
Characterizing Observations of Cometary Electrons with Kappa Distributions
Wednesday, 16 December 2015
Poster Hall (Moscone South)
Thomas W Broiles1, George Livadiotis2, James L Burch2, Raymond Goldstein2, Kathleen Mandt2, Jerry Goldstein2, George B Clark3, Stephen A Fuselier2, Marilia Samara4, Thomas Cravens5, Anders I Eriksson6, Henri Pierre7, Prachet Mokashi1 and Kyung Chae2, (1)Southwest Research Institute San Antonio, San Antonio, TX, United States, (2)Southwest Research Institute, San Antonio, TX, United States, (3)Catholic University of America, Washington, DC, United States, (4)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (5)University of Kansas, Lawrence, KS, United States, (6)IRF Swedish Institute of Space Physics Uppsala, Uppsala, Sweden, (7)CNRS, Paris Cedex 16, France
Abstract:
The Rosetta spacecraft arrived at the comet 67P/Churyumov-Gerasimenko on August 6, 2014. Since that time, Rosetta’s Ion and Electron Sensor (IES) has made near continuous measurements of the ions and electrons between 4.1 eV/q to 18.3 keV/q. Electron observations are of particular interest, because the electron distributions are highly variable in both temperature and density. At the comet, the thermal and non-thermal electron populations are non-Maxwellian, and the low-energy population has been previously described as a flat-top distribution. Here, we characterize the electrons near the comet as two kappa distributions. The kappa distribution improves upon previous work because it relates the distribution back to statistical properties such as density and temperature. Additionally, the kappa distribution allows us to determine the electron population’s departure from thermal equilibrium, which has never been studied at a comet. We find that both the low-energy and high-energy electron populations are well characterized by a kappa distribution. Moreover, the low-energy population varies on the time scale of minutes, which suggest a rapidly changing magnetic connection of the spacecraft to the low-energy electron source region.
