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Last Updated: Monday, 4 July, 2005, 05:59 GMT 06:59 UK
Nasa probe strikes Comet Tempel 1
A perfect 4 July for Nasa

US space agency (Nasa) scientists are celebrating after seeing a probe crash into the heart of a comet.

The washing machine-sized "impactor" collided with Comet Tempel 1 at a relative speed of 37,000km/h, throwing up a huge plume of icy debris.

The probe's mothership, the Deep Impact spacecraft, watched the event from a safe distance, sending images to Earth.

"We hit it just exactly where we wanted to," said an ecstatic Dr Don Yeomans, a Nasa mission scientist.

"The impact was bigger than I expected, and bigger than most of us expected. We've got all the data we could possibly ask for."

Comets - giant "dirty snowballs", as some have called them - are believed to contain materials that have remained largely unchanged since the formation of the Solar System 4.6 billion years ago.

Scientists hope that by getting "under the skin" of Comet Tempel 1, they can gain new information on the Solar System's original composition and perhaps even how life emerged in our corner of the Universe.

Waiting for the crash

Agency staff working on the $333m mission cheered, clapped and hugged when the first pictures of the impact came through to the control room at Nasa's Jet Propulsion Laboratory (JPL) in California.

The "impactor" in sight of its target     Artist's impression: Maas Digital

Dr Charles Elachi, director of JPL, said: "From the beginning, I said this was one of the most daring missions and now we have success."

"We are in the business of opening new frontiers in the exploration of space. When we analyse the data, we will have a whole new insight into the Universe."

The collision occurred at just after 0550 GMT at a distance of about 133 million km from Earth.

One of the last images from the impactor (Image Courtesy Nasa/JPL-Caltech/UMD)
Heading for impact: The comet's surface was seen by the probe to within seconds of the crash
The 370kg probe was released from the Deep Impact spacecraft on Sunday, and essentially waited to be runover by the comet, as the mothership stood back at some 500km with its cameras rolling.

In the moments before impact, the probe itself relayed pictures of the looming 14km-wide mass of ice, dust and rock. Large circular craters could be seen on the comet's surface.

The impactor's last image was sent just three seconds before impact.

It will take a few days for all the data from Deep Impact's observations to download, and scientists will then spend several months interpreting it.

All vantage points

Researchers were uncertain as to the size of scar their impactor would leave on the comet. It was conjectured to be anywhere from the size of a large house to a football stadium and between two and 14 storeys deep.

Control room delight
Delight at Nasa's Jet Propulsion Laboratory
Their studies will have the benefit of pictures taken by a range of different telescopes around Earth.

Some of the biggest and most expensive instruments were deployed, including the Hubble space observatory in its orbit above the planet, and the world's largest optical telescope facility, the VLT in Chile.

UK planetary scientist Dr Monica Grady, from the Open University, watched a feed of the Deep Impact images sent down to Earth.

"It's absolutely fantastic to see this," she said. "Before we knew so little about the comet nucleus; we had little idea of what the surface looked like.

I'm not so sure of the benefits that this expensive line of research will prove/disprove
Colin Grant, Manchester, UK

"We now have these high-resolution images and can compare this crater against natural ones. We're going to get so much out of this."

And Professor Iwan Williams, from Queen Mary, University of London, who is working on Europe's Rosetta mission to a comet, was also taken aback by the scale of the event.

"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."

See images of the comet's collision

Comet crash clues for Europe
04 Jul 05 |  Science/Nature
Q&A: Deep Impact comet mission
04 Jul 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 |  Sci/Tech

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