Scientists have a new explanation for what makes the Red Planet so red.

Recent experiments show that regular sand, when combined with black Martian basalt, takes on a reddish hue as it's crushed into dust, whether or not water or oxygen is present. Researchers from Aarhus University in Denmark claim that Mars' red dust could have formed without the water that current hypotheses hold once covered the planet.

"Mars should really look blackish between its white polar caps, because most of the rocks at mid-latitudes are basalt," said physicist Jonathan Merrison in a press release. "For decades we assumed that the reddish regions on Mars are related to the water-rich early history of the planet and that, at least in some areas, water-bearing, heavily oxidized iron minerals are present."

But when Merrison and his team mixed sand with a mineral called magnetite, found in Martian basalt, they found that mechanical stimulation alone produced a fine red dust. To simulate sand transport on Mars, the scientists tumbled pure quartz in a hermetically sealed flask for seven months, flipping each flask 10 million times. By the end of the experiment, 10 percent of the sand had turned to dust, and it became redder and redder with the addition of magnetite.

"Subsequent analysis of the flask material and dust has shown that the magnetite was transformed into the red mineral hematite, through a completely mechanical process without the presence of water at any stage of this process," said Merrison, who presented the work yesterday at the European Planetary Science Congress in Germany.

Although the scientists don't understand how the black mineral converts into the red one, they think it's due to a chemical reaction with the eroded sand. Because the experiment works not only in air, but also in a dry carbon dioxide atmosphere like the one on Mars, the researchers say simple grinding is a plausible explanation for how Mars got its striking color.

Image: Scientists say Mars should look black like the planet on the right, but may have turned red through a mechanical grinding process.

NASA/ESA/Hubble Team.

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