... The crater, named Herschel after the 1789 discoverer of Mimas, Sir William Herschel, spans about 130 kilometers and is pictured above. Comet Siding Spring Passes Mars . ... In fact, Comet C/2013 A1 (Siding Spring) passed closer to the red planet than any comet has ever passed to Earth in recorded history. ... This looks like a near miss but the greenish coma and tail of Comet Siding Spring (C/2013 A1) are really 2,000 light-years or so away from the stars of open cluster Messier 6. ... October . ...