NASA’s NEOWISE [asteroid-hunting] mission detected comet C/2013 A1 Siding Spring on July 28, 2014, less than three months before this comet’s close flyby of Mars on Oct. 19. NEOWISE took multiple images of the comet, combined here so that the comet is seen in four different positions relative to the background stars… [More at link]
More about Comet Siding Spring and its Mars encounter.