Comet C/2013 A1 (Siding Spring) was discovered on January 3rd, 2013, by prolific comet hunter Rob McNaught, analyzing images recorded by the Siding Spring Survey in New South Wales, Australia . It shouldn't surprise you if the name "McNaught" name sounds familiar in the context of comets - to date, Rob has discovered an astonishing eighty-two comets! This one bears the name "Siding Spring" because it was recorded by sky survey images, in much the same way that Comet ISON was named after the International Scientific Optical Network.
At time of discovery, C/2013 A1 was well outside of the solar system - over 7AU (650-million miles, 1-billion kilometers) - and appears to be a dynamically new object from the Oort Cloud. However, the latest orbital parameters for the comet seem to indicate that its passage through the inner solar system will see it become gravitationally bound to our Sun, and thus a long-period comet. However, the orbital period will be on the order of a million years, so don't expect to see comet Siding Spring come back any time soon!
In many ways, this is a fairly unremarkable comet. We don't think it's enormously big, and from Earth will not become particularly bright. However, this comet is going to do something never witnessed before: fly within just 86,000 miles (138,000 kilometers) from the planet Mars! This is an extraordinarily close approach for a comet, whose dusty and gassy comae can extend tens of thousands of miles from the central nucleus of the comet. This means that Mars could possible pass through the outer regions of Comet Siding Spring's coma, perhaps bombarding the planet's atmosphere with microscopic dust particles.
For the spacecraft orbiting and roving Mars, we think the risk of impacts from dust or ice is quite small. However, the risk is not zero and we don't know exactly how small it is. Even tiny sand-grain sized dust and rocks can be hazardous to spacecraft if they strike with the extremely high velocities they reach in space. Thus, the CIOC has been tasked with encouraging and facilitating a global observing campaign for comet C/2013 A1, that will hopefully provide us with enough data and information about the nature of the comet to be able to model and predict the dust environment for our Martian fleet, and assess the risk levels. The close encounter itself will occur on October 19, 2014, but the time of equal or greater concern occurs around two hours later when Mars will pass very close to the tail of the comet. Both of these events are of interest to us and will be the subject of modeling and discussion over the coming months.
For a more detailed discussion of the risk assessment for the Mars fleet of spacecraft and rovers, we have NASA PDF presentation [7.4MB] that discusses the results from modeling efforts by a team of experts. If you find that language in there a tad heavy reading, or just want a summary of the conclusions, check out the accompanying blog post by CIOC member Karl Battams.
There are a huge (perhaps unprecedented) number of space-based observations planned for the comet from both NASA and ESA spacecraft. Rather than list all of the right here, it would be better to check out the agendas and presentations give in our August 2014 and September 2014 workshops. Also we have an Observation Plans Calendar which lists many space and ground based observing efforts. For more details on the Mars mission plans you can also go to the ESA Mars Express site and the NASA Mars site. Finally some of our blogs have covered observations, such as the rather exciting potential offered by the newly arrived MAVEN spacecraft.
For the latest information on the comet's status, check out our Current Status page, which includes an up-to-date light-curve for the comet and miscellaneous notes for observers.