Comet Snowball near Mars
A comet the size of a small mountain is about to skim past Mars, and NASA hopes its spacecraft will be able to photograph the once-in-a-million-years encounter. The comet, known as Siding Spring (C/2013 A1), is set to hurtle past Mars at a close distance of about 141,600 kilometeres. The closest pass is expected to happen on Monday at 4.27 am AEDT. Astronomers do not expect it will come any where near colliding with Mars, but they do hope it will be close enough to reveal clues about the origins of the solar system. That is because the comet is believed to have originated billions of years ago in the Oort Cloud, a distant region of space at the outskirts of the solar system. The comet is flying through space at a breakneck speed of 200,000 kilometres per hour. Another interesting thing about the comet, about a mile wide in diameter, is that it is only about as solid as a pile of talcum powder.