Comet West (C/1975 V1) as seen on March 9, 1976 (Photo: NASA)
The Oort cloud of comets circles the Sun out to a distance of about a light-year (Photo: NASA)
The first comet discovered this year, Comet C/2013 A1, is currently projected to pass within about 23,000 miles (37,000 km) of the surface of Mars late in 2014. While this event in itself promises spectacular views for astronomers, the uncertainty of the comet's orbit includes a significant chance of an impact on Mars. If this happens, the impact would be hundreds of times more powerful than the asteroid impact that wiped out the dinosaurs on Earth.
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