American Astronomical Society, DPS meeting #45, #313.18 Published in Oct 2013 The Comet 2013A1 (Siding Spring) will pass within 123,000 km of Mars on October 19, 2014 at a relative velocity of 56 km/s. The comet coma will impinge directly on the Martian upper atmosphere, causing significant perturbations.We examine the thermal effects of the encounter with a first principle model of the upper atmosphere (100-200 km) that solves for the time-dependent thermal structure. The thermal model includes solar EUV heating, radiative cooling, thermal conduction, and heating due to the impact of H2O molecules from the coma.Assuming a H2O production rate...