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Last Updated: Monday, 4 July, 2005, 17:38 GMT 18:38 UK
Comet crash clues for Europe
By Paul Rincon
BBC News science reporter

Comet Tempel 1 collision viewed by the Hubble telescope

As Nasa controllers whooped and cheered in California at news of Deep Impact's success, their efforts were being watched intently by scientists in far-off London.

Through a live link to a news conference in London, UK space scientists were sharing in some of the delight and fascination of Deep Impact's American team.

This was due in part to the enormous amount of information scientists are certain to glean from the collision.

And British researchers have been observing the collision from telescopes around the world, including the Faulkes Telescope and United Kingdom Infra-Red Telescope (UKIRT) in Hawaii, The INT Telescope in Spain and the UK Schmidt telescope in Australia.

But many of the scientists here are also involved in a European mission called Rosetta which aims to orbit and land on a comet for the first time.

Comet chaser

Deep Impact, they told reporters, would give valuable insights into what lies in store for the European spacecraft, which was launched in February 2004 on a 10-year trek to Comet 67P/Churyumov-Gerasimenko.

"Deep Impact is beautiful preparation for Rosetta," said Dr Andrew Coates, of the Mullard Space Science Laboratory (MSSL) at University College London.

A perfect 4 July for Nasa

Rosetta is not designed to crash into its target. Instead, it will catch up with "CG" in 2014 after flybys of Earth, Mars and the asteroids and a three-year period of deep space hibernation.

"Anything we can do to find out more about cometary surfaces is important," Dr Coates told the BBC News website.

The Rosetta flyby spacecraft drops its lander craft towards the surface of CG. The lander then fires a harpoon to anchor it to the comet's surface.

A soft landing is a particular problem given the extremely weak gravitational force exerted by the comet nucleus. The lander, which weighs 100kg on Earth, will on the comet be as light as a sheet of paper.

If there were a slight recoil, it would bounce back like a rubber ball. To prevent this, the lander's three legs are equipped with special shock-absorbers and are fitted with ice pitons which bore into the ground immediately on touchdown.

Surprise output

"One of the big unknowns [of the Rosetta mission] is the internal structure of the nucleus, how it sticks together and the strength of the material," Dr Gerhard Schwehm, Rosetta's project scientist told the BBC News website.

"These are things we hope to learn now from the science of Deep Impact. They help us pin down our scenario when putting the [Rosetta] lander on the nucleus."

Even if they wanted to, the Rosetta team would not be able to make any big changes to the landing stage of the mission. But knowing more about the surface they are landing on will allow mission scientists to check their models of the touchdown, says Dr Schwehm.

Rosetta artist's impression, Esa
Rosetta will aim to land on a comet
Rosetta's Philae lander will determine the composition of surface and subsurface materials using spectroscopy and sample analysis. It will also take high-resolution photographs, and carries a radar to determine the internal structure of the comet's nucleus.

One of the big surprises about Monday's impact was the unexpectedly large amount of material excavated by the collision between Tempel 1 and Deep Impact's projectile.

It had been thought that the impact would excavate as much material in 15 minutes as the comet usually discharges in a month.

"I would say it's more like a year," commented Professor John Zarnecki, a space scientist at the Open University in Milton Keynes.

Early interpretations

Scientists made some early interpretations. Firstly, Comet Tempel 1's crust is probably weaker than expected.

Professor Zarnecki said it also suggested the material in the comet was probably brittle, a bit like breeze block. Dr Coates likened it to compacted snow.

Dr Schwehm said he thought that a build-up of gases just beneath the surface might have contributed to the large plume.

"When it was triggered by the impactor, they just came out," he said.

But scientists allayed fears that the impact might throw the comet off course, perhaps on a collision course with Earth.

"It was like a mosquito hitting a 747. What we've found is that the mosquito didn't splat on the surface; it's actually gone through the windscreen," explained Professor Iwan Williams of Queen Mary, University of London, and a co-investigator on Rosetta.

Though Tempel 1 poses no current threat to Earth, other cometary bodies have wrought devastation on our planet in the geological past. An asteroid or comet impact is blamed for wiping out the dinosaurs at the end of the Cretaceous Period.

"Sixty-five million years ago, one of these things took out the dinosaurs," said Faulkes Telescope director Paul Roche, before the collision. Now, he said, "we're going to get our own back".

See images of the Deep Impact collision

Nasa probe strikes Comet Tempel 1
04 Jul 05 |  Science/Nature
Q&A: Deep Impact comet mission
04 Jul 05 |  Science/Nature
Animated Guide: Deep Impact
28 Jun 05 |  Science/Nature
Chase is on for comet spacecraft
28 Apr 05 |  Science/Nature
Comet mission's images are blurry
29 Mar 05 |  Science/Nature
Comet mission set for 2005 launch
15 Dec 04 |  Science/Nature
Nasa to crash probe into comet
27 May 01 |  Science/Nature

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