... 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. ... After making quite a show in the northern hemisphere in early January of 2007, the comet moved south and developed a long and unusual dust tail that dazzled southern hemisphere observers. ...