Chandra, HST, and NASA/Irtf Observations of Comet C/2013 A1 (Siding Spring)’s Encounter with Mars

Abstract:

On Oct 19th of this year, circa 18:30 UT, dynamically new Oort Cloud comet C/2013 A1 (Siding Spring) will fly within 138,000 km of the planet Mars. This distance is so small (~1/3 the mean Earth-Moon distance, and 16 times closer than any comet has approached the Earth in the modern spaceflight era) that Mars will be moving through the comet's outer atmosphere, or coma, carrying Mars, and its orbiting and ground based roving spacecraft fleet with it. In this way the Mars fleet will be participating in a close comet flyby, and in addition to supporting the encounter by leading NASA's CIOC campaign, our group is also obtaining remote sensing observations of the comet in September - October 2014. We have received 5 partial days of observing time in late September at the NASA/IRTF facility, when the comet is brightest from the Earth, to use the SPeX NIR spectrometer at 2-5 um to measure the comet's gas and dust production contemporaneously with the BOPPS balloon mission. We have also obtained 54 ksec of Chandra time and 10 orbits of HST time to monitor the comet's nucleus, dust, and the gas/ion interaction and x-ray emission from the comet and Mars during the close encounter on 19-20 October 2014. Both the comet and Mars are known x-ray emitters, and Mars' flight through the comet's outer coma downstream wrt the solar wind suggests there will be an important transfer of gas and ions into the Martian exosphere, enhancing the Martian x-ray signal.

In this paper we report on our preliminary results from the Chandra, HST, and IRTF observations and put them in context with other observations taken during the Comet Siding Spring Observing Campaign.