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Last Updated: Wednesday, 7 September 2005, 19:48 GMT 20:48 UK
Comet shakes conventional wisdom
By Paul Rincon
BBC News website science reporter, Cambridge

Comet Tempel 1 after impact, Nasa
The collision was caught on camera by the Deep Impact flyby craft
The Deep Impact comet collision is helping astronomers piece together the early ingredients that went into making the Solar System.

Comets are thought to contain material relatively unchanged since the formation of the Solar System 4.6 billion years ago.

Spitzer Space Telescope data confirms the presence of many expected cometary ingredients, but others are a surprise.

Details have been presented at a scientific meeting in Cambridge.

Smashing probe

In July, the Deep Impact spacecraft released a 372kg projectile into the path of Comet Tempel 1. This "impactor" smashed through the surface, kicking out a massive plume of dust, gas and ice.

The explosive moment of impact on Comet Tempel 1

Spitzer was observing the dramatic collision using its infrared spectrometer. The results show that Comet Tempel 1 contains clays, carbonates and hydrocarbons amongst other ingredients.

Spitzer scientist Carey Lisse, of Johns Hopkins University, US, presented the results at the American Astronomical Society's Division of Planetary Sciences meeting in Cambridge, UK.

Seeds of life

Comets are thought to be cosmic time capsules, containing "pristine" material unchanged since the formation of the Solar System 4.6 billion years ago.

They are also thought to have seeded Earth with the chemical building blocks required for life. By analysing the material ejected from Tempel 1, scientists hope to learn more about how our Solar System formed and how life got started on our own planet.

The various pieces are held together so weakly that you could break them up on any spatial scale
Michael A'Hearn, University of Maryland
The presence of carbonates and clays is intriguing, said Dr Lisse, because of the light they shed on the character of the early Solar System.

These substances can only form in the presence of liquid water; so if the material inside Comet Tempel 1 is relatively pristine, then the early Solar System must have been a churning mass, allowing lots of mixing between the planetary building blocks.

"The material is unbelievably fragile," said Dr Mike A'Hearn, principal investigator on the Deep Impact mission. "You could pick up a chunk of it like you were picking up good powdered snow for skiing, except it would mostly be dust.

"The various pieces are held together so weakly that you could break them up on any spatial scale, big or small."

Rosetta stumped

Although a fascinating result, it spells bad news for the European Space Agency's Rosetta mission, which seeks to put a lander on comet Churyumov-Gerasimenko in 2010.

Philae and Rosetta.  <i>Esa</i>

Now, Dr A'Hearn says the powdery structures might pose problems for Rosetta's lander Philae, which has to grip on to the surface.

The Philae lander would use its mechanical legs to dig diagonally into the surface of Churyumov- Gerasimenko to hold itself down.

"It means it's really hard to understand how you're going to attach the Rosetta lander to the surface. They have to think about that seriously," Dr A'Hearn told the BBC News website.

"How it's going to work with this incredibly weak stuff, I'm doubtful. I don't think the gravity's strong enough for it to sink in, but if there is any outgassing that will whip it back up."

But Dr Bernard Foing, chief scientist at the European Space Agency, said that comets were a diverse group of objects and that scientists had designed the Rosetta mission to cope with a range of different landing scenarios due to the uncertainty over the nature of comets.

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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