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NASA's images of Mars are the wrong color

NASA has had to admit that the colours are wrong in most of the images of Mars taken by their latest mission.

Observers have been complaining that the latest pictures of the Red Planet are too red. Everything in the pictures appears red - rocks, dust, sky - even the green, blue, yellow and red paint on the probes themselves, which should have been used to calibrate the colour in these pictures!

The surface of Mars looks red, as most people would expect, in the red-tinted photographs. But what is the true colour of the landscape in these pictures? Unfortunately, if America did find life on Mars, especially simple life like blue or green algae or plants living on the surface, the false colouring of these pictures would conceal it.

The US landed two probes, Spirit and Opportunity, on 4 and 25 January 2004. A British probe, Beagle 2, landed on Mars on 25 December 2003, but we never saw any pictures from this mission, and nobody knows what happened to it after the last signals it broadcast moments before touch-down.


New Scientist, "Seeing red on Mars", p 19, 31 January 2004.
[ http://archive.newscientist.com/secure/article/article.jsp?rp=1&id=mg18124323.000 ]
    NASA has safely landed its rovers. But can it handle the conspiracy theorists? David L. Chandler investigates
    THE rolling landscape of red soil is strewn with dark rocks. NASA's brace of rovers have certainly confirmed the picture we have come to expect of Mars. But take a closer look at the images they have been sending back. Is the Red Planet really, well, quite this red?
    Welcome to the latest space conspiracy theory. The soft version of the story claims that in a bid to make an ordinary-looking, brownish Mars live up to its billing, NASA has been naughtily tweaking the colours in Spirit's digital images. The hard version has the evil NASA doctoring the colours so the rest of us won't notice evidence of life, such as patches of green.
    Leaving aside the question of why NASA would want to hide such a momentous find, has it been taking liberties with the colours? Talk to NASA's image experts and you discover that getting the colours right is a surprisingly difficult - and, despite the technical wizardry involved, subjective - job. In fact, truly accurate results, the specialists agree, are not going to happen until people have been to Mars and seen its colours first-hand.
    That said, there are problems related to these Mars rover images, some of them preventable. And in failing to make it clear just what we are seeing, NASA has naively allowed conspiracy theorists a field day.
    Although there are standard red, green and blue (RGB) filters on board that can produce a fair approximation of "true" colour, these have hardly been used. Instead, most of the colour images displayed so far have been taken through green, blue and infrared filters (IR-GB). When the infrared gets rendered as red, the results are pretty close to true, but with some really glaring exceptions. Blue and green, in particular, just don't come out right. As far as we know, those colours don't exist anywhere on the surface of Mars. If they did, we would have noticed them in the few images that have been produced using a normal red filter.
    But they are to be found on the spacecraft itself - hence the conspiracy theories. Standard blue and green paints, it turns out, are extremely reflective in the infrared, even though they hardly reflect any red light at all. So the red-yellow-green-blue colour targets installed on each rover, as well as the bright blue NASA logo, look very strange indeed. So does the blue insulation around much of the wiring. The blue paint reflects more than three times as strongly in infrared as it does in blue. So when the pictures taken with IR-GB filters are printed as RGB, the result is that the red pigment overwhelms the blue and you see a deep burgundy or even, with the insulation, a hot pink. Similarly, the green reflects more than twice as much infrared as it does green, so the green colour patch ends up a sort of mustard colour.
    Why have they been doing this? Jim Bell of NASA tells me that it's because the important thing is to get the information the geologists need to distinguish rock types, and to tell dusty rocks from clean ones. And for that, infrared is much more useful than red; hence its use for the main panoramic images we have been seeing.
    That's just part of it, though. Because of the reddish dust that is always in the air, the light falling on the surface of Mars is red to begin with; the effect is likely to be rather like terrestrial lighting close to sunset, when hills take on a pink or magenta hue. And the quality of Mar's red light will depend greatly on the level of dust as well as the time of day. That's a problem for NASA because the panoramas it has been showing us are mosaics assembled from dozens of separate frames. It may take months of fine-tuning to get the colours consistent between frames.
    Still, Bell says, compared to the initial images from Viking, which were way too red, even the initial images from this mission have been closer to what things would really look like there. Better still for Bell, nobody is in a position to argue with him. Until of course someone goes there to check.

BBC News, "Beagle 'might be in a crater'", 29 December 2004.
[ http://news.bbc.co.uk/1/hi/sci/tech/3354271.stm ]
    Beagle 2 may have fallen down a crater on Mars recently discovered near where the lander was due to touch down, scientists on the project have said.
    The crater has been discovered on Isidis Planitia, a flattish basin where Beagle was targeted to land.

"The Insider" mailing list article, 01 February 2004.

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Tags: Mars, pictures, colors, red, colour, images, false, colour, NASA, colours, Opportunity, Spirit, Beagle 2, extraterrestrial, life, Cydonia, face, Isidis Planitia, aliens, , conspiracy theories.

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