RT @esaoperations: #SidingSpring comet now 5 million km from Mars centre – same as closest approach to Earth of Halley’s comet on 10 April 1837 #MarsComet
RT @esaoperations: #SidingSpring comet now 5 million km from Mars centre – same as closest approach to Earth of Halley’s comet on 10 April 1837 #MarsComet