Abstract : On October 19th 2014, Mars experienced a close encounter with Comet C/2013 A1 (Siding Spring), at a distance of ~138,000 km. The coma washed over Mars and the planet passed directly through the cometary debris stream, producing significant effects in Mars' upper atmosphere. We present here an overview of ionospheric measurements performed during the comet encounter with Mars Express, MAVEN, and Mars Reconnaissance Orbiter. We discuss the comet's influence on the ionosphere through different processes that work at different altitudes: magnetospheric disturbances, impact of cometary pickup ions, and deposition of cometary dust.
