Even in colour, Comet 67P is grey

By Jonathan Webb
Science reporter, BBC News

image copyrightESA/Rosetta/MPS
image captionScientists superimposed images taken with three different filters

The first colour image from the Rosetta spacecraft shows that Comet 67P is even more dark and monochrome than expected.

Despite being carefully assembled from three images taken with red, green and blue filters, the shot still looks effectively black and white.

It comes from the Osiris camera, which is on board the orbiting craft that last month made history by dropping a lander onto the comet's surface.

The Osiris team says 67P is "as black as coal" and surprisingly uniform.

The image was released by the Max Planck Institute for Solar System Research, which leads the consortium behind the camera.

"We like to refer to Osiris as the eyes of Rosetta," said the instrument's principal investigator Dr Holger Sierks.

But the camera is unlike human eyes, and so the colour image had to be produced by combining three separate shots.

This was no easy task. Rosetta is constantly moving and the comet beneath is spinning, so various changes in angle had to be accounted for.

The result is an image that looks remarkably similar to previous, greyscale views of 67P.

"As it turns out, 67P looks dark grey, in reality almost as black as coal," Dr Sierks said.

By the time the image is brightened enough for us to see the comet's features, it looks much lighter grey - but not what anyone would call colourful.

Using observations from the ground, scientists had already observed that Comet 67P, like many other small bodies in our Solar System, appeared to be grey "on average".

But the new results reveal that it seems to be this dark, coal colour all over - with little variation.

That suggests that its surface composition is fairly uniform and shows no sign of ice patches, which would appear bluish.

The comet's ice is presumably hidden below its dusty, boulder-strewn surface.

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