Image Credit & Copyright: NASA/JPL
Maybe Comet C/2013 A1 Siding Spring thinks Mars is a giant pumpkin careening around the Sun just in time for Halloween or maybe it’s just a near miss event set to occur on October 19, 2014 with the potential to result in some spectacular images and or data from the team of orbiting and roving spacecraft now breathing a sigh of relief after learning that the comet will not be impacting as some had initially believed.
Let’s take a few steps back and start from start. This comet named C/2013 A1 (Siding Spring) was discovered by great Australian comet hunter Robert McNaught. That’s right, the same McNaught that discovered C/2006 P1 (Comet McNaught), the last bright comet that was obliging enough to give Earth a show back in 2007. The name Siding Spring comes from the name of the Siding Spring Survey in New South Wales, Australia that it was discovered at (link below). This is a very common practice as PANSTARRS and ISON were both named after their founding observatories.
When it was initially discovered on January 3, 2013 there was obviously no record of its history so precovery (archival observations) images of the comet dating back to early December of 2012 were gathered from known images in that general location and a rough trajectory was then established. That data coupled with current observations at that time placed the comet on an orbital trajectory that would come extremely close to the Red Planet.
As longer, current observations have come in; closest approach estimates are currently at 82,000 mi (132,000 km) and scheduled to occur on October 19 at 18:28 UTC (14:28 EDT). For perspective, that distance is almost six times further than Mars most distant moon Deimos at apoapsis. If it were passing Earth it would be almost five times the distance of asteroid 2012/DA 14 as it passed Earth on February 15, 2013 (but not as close as the Chelyabinsk meteor) and about one-third of the distance to the Moon. That being said; according to NASA this pass of Mars will be only one-tenth the distance of any known pass of Earth by a comet.
As far as danger to spacecraft, NASA has planned to position its three (once MAVEN arrives in Sept to join Odyssey and MRO) on the opposite side of the planet during close approach. Even then, the major worry during this entire period will come about 90 minutes later and last for a period of about 20 minutes as Mars passes through the fresh debris field. It doesn’t appear at this time that Curiosity and Opportunity will be in any danger but they, along with their team of orbiters will have their eyes on the comet as it approaches, departs and will monitor its effects on the Martian atmosphere thereafter.
Incredibly, if you live in the southern hemisphere there’s a chance you can see this encounter with binoculars or telescopes. Currently the comet is at an apparent magnitude of 9.3 and brightening and in the constellation Horologium. By the time October 19 rolls around, the pair will be in the constellation Ophiochus and low in the southwestern sky at dusk so dust off your equipment and hope for some clear skies!
The Sky LIVE (Real Time Tracking): http://theskylive.com/c2013a1-info
NASA Mars Exploration page on C/2013 A1: http://mars.nasa.gov/comets/sidingspring/
NASA JPL Info Page on Comet C/2013 A1: http://neo.jpl.nasa.gov/news/news179.html
NASA JPL Data Page on Comet C/2013 A1: http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2013A1;cad=1#cad
ISON-NM Leonid Elenin data on C/2013 A1: http://spaceobs.org/en/tag/c2013-a1-siding-spring/
Siding Spring Survey (SSS): http://www.mso.anu.edu.au/~rmn/
NASA Solar System Simulator: http://space.jpl.nasa.gov/
NASA Eyes on the Solar System: http://eyes.nasa.gov/download.html