Ion cyclotron waves near comet C/2013 A1 (Siding Spring) and Mars

Thursday, 18 December 2014
Frank J Crary1, Vincent J Dols1, John E P Connerney2 and Jared R Espley2, (1)University of Colorado at Boulder, Boulder, CO, United States, (2)Goddard Space Flight Center, Greenbelt, MD, United States
 On October 19, 2014, comet C/2013 A1 (Siding Spring) passed approximately 135,000 km from Mars. Previously,
we predicted the amplitude of ion cyclotron waves which might be observed during the Siding Spring encounter. Ion
cyclotron waves have been observed both in the vicinity of comets and of Mars. These waves are generated by the
ionization of neutrals in the flowing solar wind, which produces an unstable ring-beam velocity distribution. We 
estimated that, for a production rate of 2x1028 s-1, ion cyclotron wave with amplitudes over 0.1 nT would be present 
within ‡5 hours (1.2 million km) of closest approach.
 We will compare the actual observations made by the MAVEN spacecraft with these predictions. The spacecraft 
was close to or downstream of the martian bow shock, which complicates the interpretation of the data. Taking this
into account, we will describe the observations and their implications for wave activity and cometary neutral production.
 We also present updated hybrid simulations of ion cyclotron wave generation. The simulations use our best 
estimate of solar wind conditions at the time of the encounter and a variable injection of 18 AMU pickup ions, at a 
rates consistent a model of the cometary neutrals.