Comet C/2013 A1 (Siding Spring) was discovered in January 2013 by Robert McNaught. Early orbit calculations suggested it is a hyperbolic comet, i.e. either coming from the Oort Cloud (an inferred structure at the edge of the Solar System, barely bound to the Sun) or from an other planetary system. Therefore, C/2013 A1 represents a unique opportunity to study the outskirts of the Solar System.

Most surprizingly, the calculations showed that the comet would pass very close to the planet Mars in October 2014. Earth- and Mars-based assets, like the ESO Very Large Telescope and the ESA Mars express spacecraft, will be able to perform exceptional observations when the comet gets close to the planet.

The latest orbit determinations have put the flyby distance at 110,000 km from the surface of Mars: any collision with the planet has been ruled out for now. The comet will pass close to Mars on October 19th, 2014, at 18:41 UTC (with a time uncertainty of about 30 min). The relative velocity will be about 56km/s. The lastest updates on the flyby parameters are available here.