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Last Updated: Wednesday, 13 July, 2005, 18:50 GMT 19:50 UK
X-rays show depth of Deep Impact
Comet Tempel 1 after impact, Nasa
The collision was caught on camera by the Deep Impact flyby craft
Scientists have been studying the X-ray light around Comet Tempel 1 after its collision with the Deep Impact probe - to gauge the size of crater created.

The US space agency's (Nasa) Swift satellite recorded the high-energy light, which got brighter and brighter over the weekend of 9-10 July.

The X-rays were produced by dust kicked up during the impact and thus indicate how big a hole was left in the comet.

Researchers say tens of thousands of tonnes of debris was released.

This will provide fascinating information about a comet's atmosphere
John Nousek, Penn State University
"Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source," said Paul O'Brien, of the Swift team at the University of Leicester, UK.

"How things change when you ram a comet with a copper probe travelling over 20,000 miles (32,000km) per hour.

"The X-ray light we detect now is generated by debris created by the collision combined with material naturally coming off the comet."

Solar winds

Although the actual impact occurred on 4 July, it takes several days for the dust and debris to reach the comet's upper atmosphere, or coma, where it can be illuminated by the high-energy particles, or solar wind, streaming away from the sun.

The explosive moment of impact on Comet Tempel 1

"For the first time, we can see how material liberated from a comet's surface migrates to the upper reaches of its atmosphere," said John Nousek, of Penn State University, US.

"This will provide fascinating information about a comet's atmosphere and how it interacts with the solar wind. This is all virgin territory."

Although analysis is still ongoing, scientists think enough dust was thrown up to leave a 10m (32ft) deep coating on a football pitch.

An artist's impression of the impact, AP
Artist's impression: The Deep Impact mission will reveal many secrets about comets
The Swift satellite is usually used for detecting distant natural explosions, called gamma-ray bursts, and creating a map of X-ray sources in the Universe.

However, following the Deep Impact mission to Tempel 1, it is providing the only simultaneous multi-wavelength observation, with a suite of instruments capable of detecting visible light, ultra-violet light, X-rays and gamma rays.

Swift scientists say that "different wavelengths reveal different secrets about the comet".

Professor Keith Mason, of University College London, UK, said: "Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical UV instruments in the same satellite."

Comet impact gave 'powder plume'
11 Jul 05 |  Science/Nature
Comet's huge plume hides crater
06 Jul 05 |  Science/Nature
Nasa probe strikes Comet Tempel 1
04 Jul 05 |  Science/Nature
Q&A: Deep Impact comet mission
04 Jul 05 |  Science/Nature
Swift ready for Universe's worst
05 Apr 05 |  Science/Nature

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