Azara Blog: NASA smashes probe into a comet

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Date published: 2005/07/04

The BBC says:

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."

In addition, the BBC says:

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.

Scientists made some early interpretations. Firstly, the comet'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 impact.

"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 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.

Well this mission can be considered to be either a great technological triumph or a massive act of vandalism. It's quite possible (unless NASA can prove otherwise) than in N million years the course of the comet will have been sufficiently changed that it comes back and splats Earth instead of missing it (if we are extremely unlucky), or vice versa (if we are extremely lucky). The fact that the impact was like a "mosquito hitting a 747" is neither here nor there, small differences now add up to big differences in time. A 747 can be piloted to change its course, it is not so easy with a comet.

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