Mars’ ionospheric interaction with comet C/2013 A1 Siding-Spring’s coma
at their closest approach as seen by Mars Express
Abstract
On 19 October 2014, Mars experienced a very close encounter with Comet
C/2013 A1 Siding Spring. Using data from the Mars Advanced Radar for
Subsurface and Ionosphere Sounding (MARSIS) on board Mars Express (MEX),
we assess the interaction of the Martian ionosphere with the comet’s
atmosphere and possibly magnetic tail during the orbit of their closest
approach. The topside ionospheric electron density profile is evaluated
from the peak density of the ionosphere to the local plasma around Mars
Express. We find unusual, complex and rapid variability in the
ionospheric profile along the MEX orbit, not seen even after the impact
of large coronal mass ejections. Before closest approach, large electron
density reductions predominate, which could be caused either by comet
water-damping, or comet magnetic field interactions. After closest
approach, a substantial electron density rise predominates. Moreover,
several extra topside layers are visible along the whole orbit at
different altitudes, which could be related to different processes as we
discuss.