Rosetta's comet has no ice and is 'darker than charcoal': 'Surprising' discovery made after probe sends back its first set of data
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Rosetta has uncovered some surprising features about comet 67P/Churyumov-Gerasimenko as it orbits it in deep space.
Instead of imaging a bright, ice-covered comet, the probe's instruments have detected that 67P is in fact darker than charcoal in some wavelengths of light.
And scientists working on Rosetta's Alice instrument have so far failed to find any large patches of water-ice on 67P's surface.
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An artist's impression of the Rosetta orbiter at comet 67P/Churyumov-Gerasimenko. Instead of imaging a bright, ice-covered comet, the probe's instruments have detected that 67P is in fact darker than charcoal
'We're a bit surprised at just how unreflective the comet's surface is and how little evidence of exposed water-ice it shows,' said Alan Stern, Alice principal investigator at the Southwest Research Institute in Colorado.
Scientists had previously believed the comet's surface would contain ice because it was too far away for the sun's warmth to melt it.
The lack of ice could suggest that the comet had been in close with our sun, or a different star, at some point during its journey in deep space.
They also found that the 'coma' - or atmosphere - around the comet contains of hydrogen and oxygen.
This is surprising as comas are generally thought to be composed of water vapour and dust.
Alice is now probing the origin, composition and workings of comet 67P to gather insights that can not be obtained by either ground-based or Earth-orbiting observation.
It has more than 1,000 times the data-gathering capability of instruments flown a generation ago, yet it weighs less than 9lbs (4kg) and uses just watts of power.
The instrument is one of two full instruments on board Rosetta that are funded by Nasa. The agency also provided portions of two other instrument suites.
Another U.S. contribution aboard the spacecraft is the Microwave Instrument for Rosetta Orbiter (Miro)
Miro is designed to provide data on how gas and dust leave the surface of the nucleus to form the coma and tail that gives comets their intrinsic beauty.
Described as 'the sexiest, most fantastic mission ever', Rosetta will spend more than a year analysing the comet to help uncover the secrets to life on Earth.
The comet itself is about 2.5 miles (4km) long and orbits the sun every six-and-a-half years.
It is heading towards the sun, so as it nears the star it will begin to melt more.
Zoom in on the image below to find out where Rosetta is at the moment
Five sites were identified on Comet 67P/Churyumov-Gerasimenko during the Landing Site Selection Group meeting held 23–24 August. The approximate locations of the five regions are marked on these OSIRIS narrow-angle camera images taken on 16 August from a distance of about 62 miles (100km)
For a sense of scale, the comet is about three times the size of Ben Nevis and Rosetta is the size of a car with 105ft (32 metre) wings.
In November, Rosetta will be the first spacecraft to send a probe, dubbed Philae, to explore the comet's surface.
The target drop zone for a landing on a comet in deep space will be unveiled on 15 September after weeks of analysis to find the perfect location.
Throughout this year, astronomers have been monitoring the comet using ground-based telescopes, and they will continue to follow the comet on its orbit around the sun until the end of 2015.
Until November, 67P is only visible from the southern hemisphere, and it is currently in a patch of the sky where it is camouflaged against the crowded star fields of the Milky Way.
Taken on the 14th August, this image was taken from a distance of about 62 miles (100km) from the comet
This image of comet 67P was taken with the European Southern Observatory's Very Large Telescope on 11 August. The central pixel includes Rosetta, now orbiting comet 67P, but too small to be shown in the image
At more than 500 million km from the sun, the comet is still very faint, so only visible to large professional telescopes, including the European Southern Observatory's Very Large Telescope, or VLT, in Chile.
Images of the comet are taken every two nights on average. These are quick snapshot images taken by ESO staff to monitor the comet's activity, by measuring how its brightness changes over time.
The latest image reveals the comet is now clearly active, with a dusty coma extending at least 19,000 km from the comet.
'Its brightness remains in line with predictions based on ground-based data from previous orbits of 67P/C-G, reassuring us that the comet should continue to behave according to our expectations up to the Philae landing and beyond,' Esa said in a blog.
This 3D image of comet 67P can be viewed using stereoscopic glasses with red–green/blue filters. It was created by merging two images taken last month by the Rosetta probe as it circled around the comet
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