We are scientists studying the comet about to engulf Mars on Sunday. Ask away!
This Sunday (19 Oct. 2014) at about 2:30pm ET (11:30 am PT) Comet 2013/A (Siding Spring) will pass within 140,000 km (87,000 miles) of Mars. This means that the gas cloud surrounding the comet will effectively envelop Mars while it passes by at 56 km/s (125,000 mph). The dangerous dust tail will just barely miss Mars and the orbiting spacecraft there. Observers at or near Earth (like Hubble) will watch the interaction from afar while the Mars spacecraft will get a frontrow seat to the interaction. In particular, the newly arrived MAVEN spacecraft is particularly well suited to studying the comet’s effect on the martian upper atmosphere since that’s what it’s designed to do. Both the Curiosity and Opportunity rovers will try to take photos of the comet filling the martian nightsky.
Answering questions tonight are Jared Espley, MAVEN science team member, and two members of NASA's Coordinated Investigations of Comets team who have been involved in facilitating planning and observations of comet Siding Spring, Karl Battams and Matthew Knight.
UPDATE 10:00 PM EDT We're going to wrap this up for now, but will keep checking this over the next few days and respond to new questions as we can. Thanks to everyone for participating. If you want to stay up to date on Comet Siding Spring, check out http://cometcampaign.org/ and http://mars.nasa.gov/comets/sidingspring/.
UPDATE Oct 15 1:00 PM EDT I had a few mins spare to pick off a couple more questions. Matthew and Jared will check back later to answer more, so keep them coming! [KB]
UPDATE Oct 15 6:30 PM EDT I took another swing through and answered a bunch more questions. We'll keep checking the thread, so keep asking questions, [MK]