Engineering: Nasa snaps its moment of glory as probe hits comet

A little American suicide spacecraft flew into a comet the size of a city 83 million miles from Earth, taking pictures at the rate of one a minute before it vapourised in a blast equivalent to exploding five tonnes of TNT.

The £190m mission involved split-second timing, collision speeds of 23,000mph and a triumphant series of pictures that ended with a close-up just three seconds before the craft's own destruction.

"Right now we are minus one spacecraft,"a delighted Nasa engineer said, while a colleague at the Jet Propulsion Laboratory in Pasadena said: "There is a comet in the sky wondering what the hell hit it."

Deep Impact was a July 4 fireworks display years in the making that ended in a flash.

A mothership dropped a copper projectile the size of a washing machine in the path of comet Tempel 1 at 6.52am BST yesterday and then photographed the resulting jet of ice, dust and organic chemicals from the pockmarked surface, as the explosion excavated a huge impact crater and dramatically intensified the native brightness of the mysterious visitor.

The celestial traffic accident obliterated the projectile but barely affected the comet: experts estimate that the impact would have slowed it by no more than 1/10,000th of a millimetre a second.

The aim was to probe for the first time the interior of one of the ghostly visitors that have haunted human imagination throughout history. It is likely to become one of the most intensely studied encounters ever made in space. Deep Impact's copper-coated bullet carried its own camera and radio.

The mothership steered a course 300 miles from the explosion and observed the impact, and the ensuing jet eruption, with instruments for 800 seconds. Seven satellites, including the Hubble space telescope, monitored the moment of drama, and over the next day and night an estimated 50 earthbound telescopes locked on the tiny, faraway flare.

The first to produce pictures in Britain, even beating Nasa to the draw, were pupils from King's school, Canterbury, using data from the two-metre Faulkes telescope in Hawaii, an instrument intended for schools.

But long before giant telescopes could begin to analyse the minutiae of the collision in the optical ultraviolet, infra-red and x-ray wavelengths, British, European and American astronomers and planetary scientists were enjoying a moment of triumph.

For the first time, they had clear and close-up studies of a comet. They could count the impact craters on its surface, they could hazard an early guess at its density and they could estimate the firmness of its surface from the violence of the flare after the collision. And in the gusts of material ejected from the collision crater, they could begin to see the pristine raw material of the whole solar system.

Comets are the rubble left over from the making of the solar system.

Frequent visitors such as comet Halley fly close to the sun, trailing a huge coma, and have been weathered and altered by solar radiation.

But comets such as Tempel 1 have spent most of the past 4.6bn years parked far beyond the orbit of the outermost planets.

"These icy time capsules could hold the secrets of the planets"

When they are sucked into the centre, they steer wide of the sun, and their interiors are preserved by the freezing stillness of distant space.

Because of their relative aloofness, these icy time capsules could hold the secrets of the planets, the Earth's oceans and even of the primeval organic chemistry from which life must have been fashioned.

"If you are thinking of comets as possible sources of organic material, then you want the organic elements carbon, hydrogen, oxygen, nitrogen. And we now know enough about comets to know that some of these elements are in the form of organic molecules," said John Zarnecki of the Open University.

For Andrew Coates of the Mullard space science laboratory of University College London, it was one of the most audacious experiments in history.

"You have the comet getting bigger and bigger in the field of view, the level of detail on the comet getting better and better," he said.

"We know that comets produce jets. What we have now is the first artificial jet from a comet.

"The fact that there are craters tells us the surface has a solid type of composition. We see a relatively dark surface, probably some organic molecules and silicates, and it is the composition of that mixture which is going to be really exciting."

Close encounters past, present and future

• Deep Impact is only the latest comet mission, and there are more to come
• 1985 Giotto was launched on a trajectory past comet Halley in 1986, and comet P/Grigg-Skjellerup in 1992
• 1998 Deep Space 1 was launched to test 12 high-risk technologies in space. In 2001, before its retirement, it flew past comet Borrelly
• 2004 Rosetta set off on a 10-year trek to meet comet 67 P/Churyumov-Gerasimenko. It will place a lander on the comet's surface in 2014
• 2005 Deep Impact was launched in January on a journey of 268m miles in 172 days to encounter Tempel 1

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