Space

Rosetta's Alice instrument reveals comet is blacker than charcoal

Rosetta's Alice instrument rev...
Artist's impression of Rosetta and 67P/Churyumov-Gerasimenko (Image: ESA/ATG Medialab)
Artist's impression of Rosetta and 67P/Churyumov-Gerasimenko (Image: ESA/ATG Medialab)
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Mosaic of 67P/Churyumov-Gerasimenko (Image: ESA)
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Mosaic of 67P/Churyumov-Gerasimenko (Image: ESA)
Self-portrait of Rosetta (Image: ESA)
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Self-portrait of Rosetta (Image: ESA)
Mosaic of 67P/Churyumov-Gerasimenko (Image: ESA)
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Mosaic of 67P/Churyumov-Gerasimenko (Image: ESA)
Cliffs on 67P/Churyumov-Gerasimenko (Image: ESA)
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Cliffs on 67P/Churyumov-Gerasimenko (Image: ESA)
67P/Churyumov-Gerasimenko seen from European Southern Observatory’s Very Large Telescope in Chile (Image: ESA)
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67P/Churyumov-Gerasimenko seen from European Southern Observatory’s Very Large Telescope in Chile (Image: ESA)
67P/Churyumov-Gerasimenko from a distance of 51 km (Image: ESA)
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67P/Churyumov-Gerasimenko from a distance of 51 km (Image: ESA)
67P/Churyumov-Gerasimenko on September 10 (Image: ESA)
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67P/Churyumov-Gerasimenko on September 10 (Image: ESA)
Artist's impression of Rosetta and 67P/Churyumov-Gerasimenko (Image: ESA/ATG Medialab)
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Artist's impression of Rosetta and 67P/Churyumov-Gerasimenko (Image: ESA/ATG Medialab)
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Comets are often described as "dirty snowballs" of ice and dust, which suggests something that looks like what kids throw at each other in winter. But NASA’s Alice instrument package installed aboard the ESA Rosetta probe currently orbiting comet 67P/Churyumov-Gerasimenko has sent back its first science data, which shows that the comet is about as white and fluffy as a lump of coal.

Alice is one of eleven instruments carried aboard Rosetta and one of three instrument packages supplied by NASA for the unmanned orbiter. Essentially, it’s a miniature UV imaging spectrograph that looks for thermal markers in the far ultraviolet part of the spectrum in order to learn more about 67P/Churyumov-Gerasimenko’s composition and history.

It does this by looking specifically for the markers associated with noble gases, such as helium, neon, argon, and krypton. Since the temperature at which these gases sublime is known, it’s possible to measure their presence and calculate the temperature of the comet in its past as well as its present characteristics.

According to NASA, Alice weighs less than 9 lb (4 kg) and uses only four watts of power, but it’s 1,000 times better at data gathering than similar instruments of just a generation ago. Also, it’s closer to a comet than any such device has ever been.

Self-portrait of Rosetta (Image: ESA)
Self-portrait of Rosetta (Image: ESA)

The upshot of all this high-tech imaging is the surprising discovery that 67P/Churyumov-Gerasimenko doesn’t look so much like a dirty snowball but something that came out of a coal cellar. In fact, it is black. Really black. According to NASA, it’s darker than charcoal. And though Alice has detected oxygen and hydrogen in the comet’s coma, the patches of barren ice that NASA scientists had expected aren't there. Apparently, this is because 67P/Churyumov-Gerasimenko is too far away from thee warmth of the sun to turn the ice into water vapor.

"We’re a bit surprised at just how unreflective the comet’s surface is and how little evidence of exposed water-ice it shows," says Alan Stern, Alice principal investigator at the Southwest Research Institute in Boulder, Colorado.

67P/Churyumov-Gerasimenko on September 10 (Image: ESA)
67P/Churyumov-Gerasimenko on September 10 (Image: ESA)

Launched in 2004, Rosetta reached 67P/Churyumov-Gerasimenko by a circuitous route involving three flybys of Earth, one of Mars, and a long detour out beyond Jupiter as it built up enough speed to catch up to the comet. During this time, it passed close to the asteroids Šteins and Lutetia, and went into a 31-month hibernation to conserve resources until the comet rendezvous on August 6 to start a year-long mission to study the comet to gain new insights into the early history of the Solar System. The first attempt to land on the comet nucleus is set for November.

Source: NASA

View gallery - 8 images
4 comments
Wesley Bruce
This was not a surprise to some of us. The comet is a rock not ice. The predictions of Wallace Thornhill and David Talbott date from 2009 and have so far been largely born out. http://www.bibliotecapleyades.net/electric_universe/esp_electricuniverse17.htm
The physics community just hates it when a heterodox theory is proven correct. They have been dismissed as pseudo-science for years. A black ball of charged rock is a strange and dangerous thing.
Unlike the previous comet contact probes ESA Rosetta 's designed to equalize charge so it does not get vaporized by 'space lightening'; a catastrophic discharge due to in equal charge.
While I don't agree with all their theories its clear that much more attention must be paid to their underlying ideas.
Slowburn
Just like like when they plow snow into a big pile the snow melts and the dirt that got picked up doesn't soon you have a black coating of dirt over the snow.
windykites
For something that is blacker than carbon, it is surprisingly we can see it at all. Only those areas in direct sunlight will be visible.
I cannot quite understand what happens to water in a vacuum. Presumably it turns into a vapour, due to no pressure.When it is in sunlight it cannot freeze into ice. When it is shielded from the Sun, is there sufficient gravity in the water molecules to draw themselves into a compact form of ice? I somehow doubt it.
I would be pleased if somebody could explain this to me.
Aleko Long
@windykites1
http://scienceblogs.com/startswithabang/2009/06/29/water-in-space-what-happens/