WORLD SCIENCE

"Long before it's in the papers"
August 03, 2010

Oct. 13, 2005
Special to World Science

Observations of Comet Tempel 1 made by European scientists while NASA shot a projectile into the object suggest comets are more dusty than icy, the researchers say.

The outburst from the impact on Tempel 1, as seen from the Hubble Space Telescope

The evidence hints that comets are “icy dirtballs,” rather than the “dirty snowballs” they were previously believed to be, according to the group.

The conclusions draw on measurements taken by the European Space Agency’s Rosetta spacecraft during the NASA mission, dubbed Deep Impact. Comets are believed to contain material that has been almost unchanged since the Solar System’s creation. The mission was designed to learn more about this material by slamming a probe into it. 

That happened last July 4.

The 370 kg (816 lb.) copper impactor hit the comet at roughly 10 kilometres (6 miles) per second. 

Tempel 1’s icy core, roughly the size of central Paris, contains loose material that easily comes off the surface, researchers found. Rosetta, with instruments for cometary investigations, used its capabilities to observe the comet before, during and after the impact from about 80 million kilometers (50 million miles) away.

An imaging system was used to observe the comet’s nucleus, or core, before and after the impact, tracking the dust ejected by the impact.

The scientists also measured the water vapour content of the dust spray. They then calculated there was more dust than ice. Thus it seems “comets are composed more of dust held together by ice, rather than made of ice comtaminated with dust,” the researchers said in a statement issued by the agency this week.

The scientists also hope to make a 3D reconstruction of the dust cloud around the comet by combining their images with those taken from ground observatories.

The findings are published in the Oct. 13 issue of the research journal Nature.

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