Comet Siding Spring makes close pass by Mars
 
		Spacecraft orbiting Mars hunkered down behind the planet to safely observe comet Siding Spring's close approach, as shown in this illustration. (Spacecraft are not to scale.)
JPL-Caltech/NASA
 
		Spacecraft orbiting Mars hunkered down behind the planet to safely observe comet Siding Spring's close approach, as shown in this illustration. (Spacecraft are not to scale.)
JPL-Caltech/NASA