Electron Impact Studies Relevant to Rosetta Coma Measurements of 67P/Churyumov-Gerasimenko

Auroral emission from electron impact processes can provide a remote window on the physical properties of plasma and neutral gases surrounding small bodies (Galand & Chakrabarti, 2002; Roth et al. 2014). Surprisingly, Rosetta found that outside 2 AU pre-perihelion, atomic and molecular emission features in the inner coma were predominantly caused by dissociative electron impact excitation (Feldman et al. 2015). When the comet came within 2 au of the Sun, fluorescent emission became the dominant process, as water densities in the inner coma could effectively cool the electron population below the appearance energy of the relevant electron impact dissociative excitation processes (Bodewits et al. 2016). Further quantitative interpretation of the Alice and OSIRIS images of the coma is by limited excitation cross sections measured of electron impact reactions with the gases present in cometary comae, including H2O, CO2, CO, O2, and HCN. We will present the first results of a series of experiments dedicated to investigate the emission features seen by the instruments on board Rosetta. The experimental set up is located at the Comenius University in Bratislava, Slovakia, and consists of a crossed-beam configuration combining an electron monochromator and a gas beam (Danko et al. 2013). The electron induced emission spectra are measured using a Czerny-Turner optical monochromator provides a spectral resolution of 0.3 nm FWHM and is equipped with a photomultiplier sensitive between 185 and 710 nm. References: Bodewits, D. et al. The Astronomical Journal 152, 130 (2016). Danko, M. et al. J. Phys. B 46, 045203 (2013). Feldman, P. D. et al. Astron. Astroph. 583, A8 (2015). Galand, M. & Chakrabarti, S. Geophysical Monograph 130. Ed. Michael Mendillo 130, 55- (2002). Roth, L., Saur, J., Retherford, K. D., Strobel, D. F. & Feldman, P. D. Science (2014). doi:10.1126/science.1247051