Prolonged Lifetime of the Transient Ionized Layer in the Martian
Atmosphere Caused by Comet Siding Spring
In October 2014, the close encounter between Mars and comet Siding
Spring produced a transient ionized layer in the upper atmosphere
composed primarily of Mg⁺ ions. The layer was detected by instruments on
three spacecraft, including the Mars Advanced Radar for Subsurface and
Ionosphere Sounding (MARSIS) on Mars Express. Analyses of the MARSIS
data indicated the transient layer persisted up to ~19
hours after the comet’s closest approach. We report MARSIS observations
that suggest the transient layer lasted at least 7 days – and
potentially as long as 32 days – after closest approach. During this
period, the transient layer was mostly confined to a narrow latitude
range between 20°N-60°N and a longitude range spanning 275°E to 95°E.
Since this period coincided with a highly active Sun, we discuss how
solar flares may have contributed to the layer’s prolonged lifetime.