Friday, 11 July 2008

WRONG: Mars is red

While Mars certainly isn’t green or blue, it’s no redder than, say, the Australian outback. Both are a drab, rusty brown, and Mars' sky is a butterscotch-yellow. After powerful dust storms, iron-rich particles form a yellow-brown haze. This dust absorbs light of shorter wavelengths (the blues), and scatters the yellows and reds around the sky. You can see a similar effect in any smog-laden city, or at sunset. (ie The red sky at night so popular with shepherds.)

There is nevertheless controversy over what precise colour the Martian sky is. NASA was recently accused of “tweaking” the colour of their pictures to fit with people’s expectations. Their first pictures, from back in 1977, were certainly doctored to appear blue, but only because the the scientists were unprepared for presenting their material to the press. “Several days after the first release,” said Imaging Team Leader Tim Mutch, “we distributed a second version, this time with the sky reddish. We smiled painfully when reporters asked us if the sky would turn green in a subsequent version.”

One point of interest is that Mars’ sunrise and sunset are actually blue. While the dust particles scatter away all wavelengths, their particular size relative to the angle through which the light is travelling close to the horizon causes blue light to be directed along the line from the sun to the dust particle (to the viewer), causing a blue haze.

Even stranger, Blur's bass player Alex James is a keen astronomer and was one of the first non-academics to get involved in the Beagle Mars lander project, having asked his accountant to find a way for him to go to Mars. His accountant put him in touch with Professor Colin Pillinger, who was then trying to drum up support for his proposed project.

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