It is not often we have had the opportunity for observing astronomical objects as they fly by at a relatively short distance.
In the last decades there has been one comet and a few small asteroids that passed close to Earth. But never before have we been able to observe a comet from another planet, until now.
On October 19 comet Siding Spring or C/2013 A1 will pass Mars at distance of a mere 140 000km.
MRO will attempt to take images of the comet nucleus, and the orbit have been engineered so that the spacecraft, together with Mars Odyssey and MAVEN will be somewhat sheltered on the opposite side of Mars when the planet get closest to the dust tail of the comet.
The list of orbiters, space and surface instruments as well as amateur astronomers going to observe the event is to long to get trough here.
But it is interesting to note that MRO have been cast as the Protagonist in this observing campaign from Mars. And it's a nice coincidence having nature perform a flyby of another comet putting cometary science in the highlight now that Rosetta is studying another comet at the very same time.