Comet's Close Encounter with Mars Dumped Tons of Dust on Red Planet

Comet Siding Spring's close shave by Mars last year provided a rare glimpse into how Oort Cloud comets behave, according to new research. Comet Siding Spring also left behind a substantial quantity of carbon dioxide, nitrogen and water that couldn't be detected because Mars' atmosphere is also made up of those elements. Siding Spring's journey from the Oort Cloud — a collection of comets beyond the orbit of Neptune that stretches for hundreds of astronomical units — meant it was pris