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A rare close encounter between Mars and a comet last month pummeled the Red Planet with cometary dust, which probably left a yellow glow in the Martian sky, scientists revealed Friday.
Scientists studying the Oct. 19 Mars flyby of Comet Siding Spring said they were shocked at the amount of dust the comet showered down on the Red Planet. Early estimates peg the amount at a few thousand kilograms, according to Nick Schneider, a lead scientist for the Imaging Ultraviolet Spectrograph on NASA's Maven spacecraft.
"We ended up with a lot more dust than we ever anticipated," said Jim Green, director of NASA's Planetary Science Division. "It surprised us." [Photos of Comet Siding Spring at Mars]
Green said models of the flyby underestimated the size of the comet's dust tail and overestimated how much it would spread out before reaching Mars. NASA positioned its satellites behind Mars to protect them from the dust.
Scientists using the High Resolution Imaging Science Experiment, a camera aboard NASA's Mars Reconnaissance Orbiter, announced a refined value for the size of the comet's nucleus — the solid, central portion made of rock and ice. They said the nucleus was 1.2 miles (2 kilometers), which is smaller than expected.
The falling dust particles, just like meteors in Earth's atmosphere, burn up as they go down, so the shower would have created a brilliant light show for anyone standing on Mars at the time.
Different elements can create different colors when they burn, and Schneider said it is likely the sky would have had a distinctly yellow glow due to high levels of sodium.
In the wake of the comet's passage, NASA scientists have a trove of data that will hopefully answer questions about the comet and its origins. Comet Siding Spring is from a region called the Oort Cloud, a massive ring of icy bodies beyond the orbit of Neptune.