English: This composite Hubble Space Telescope image captures the positions of Comet Siding Spring (C/2013 A1) and Mars in a never-before-seen close passage of a comet by the Red Planet, which happened at 2:28 p.m. EDT October 19, 2014. On that date the comet passed by Mars at approximately 87,000 miles (about one-third the distance between Earth and the Moon).

The Mars and comet images have been added together to create a single picture to illustrate the angular separation between the comet and Mars at closest approach.

This is a composite image because a single exposure of the stellar background, Comet Siding Spring, and Mars would be problematic. Mars is actually 10,000 times brighter than the comet, and so could not be properly exposed to show detail in the Red Planet. The comet and Mars were also moving with respect to each other and so could not be imaged simultaneously in one exposure without one of the objects being motion blurred. Hubble had to be programmed to track on the comet and Mars separately in two different observations.

The background starfield in this composite image is synthesized from ground-based telescope data provided by the Palomar Digital Sky Survey, which has been reprocessed to approximate Hubble's resolution.

For more information, visit: hubblesite.org/news_release/news/2014-45/82

Credit: NASA, ESA, J.-Y. Li (PSI), C.M. Lisse (JHU/APL), and the Hubble Heritage Team (STScI/AURA)