This is a photo composite of the encounter of Comet Siding Spring with Mars on October 19, 2014. Separate Hubble Space Telescope images of Mars and the comet have been combined together into a single picture. This is a composite image because a single exposure of the stellar background, Comet Siding Spring, and Mars would be problematic because the objects are all moving with respect to each other and the background stars. Hubble can only track one planetary target at a time. Also, Mars is actually 10,000 times brighter than the comet, and the exposure here has been adjusted so that details on the Red Planet can be seen.
Please join Hubble astronomers at 3pm EDT today for a live discussion at Comet Siding Spring and Mars Hubble Hangout.