NZ prime viewing spot for comet crash

New Zealanders with medium-powered telescopes will have one of the best chances of seeing the impact of a Nasa spacecraft slamming into a comet next week.

Nasa scientists are preparing to slam a coffee table-sized spacecraft into a comet half the size of Manhattan on July 4 in a cosmic smashup aimed at discovering the building blocks of life on Earth.

Because scientists do not know how bright the impact will be, they cannot say how easy it will be for backyard astronomers to see it. Those with the best chance are people with medium-powered telescopes in the western United States, parts of Mexico, and New Zealand, they said.

At 5.52pm NZ time on Monday (0552 GMT), 350 kg copper-fortified impactor is expected to smash into Tempel 1 at 23,000 miles an hour, a speed that would pare the flight from New York to Los Angeles down to 6 minutes.

Scientists anticipate the crash will eject a spray of ice and dust from the comet's crusty surface and reveal the material beneath it.

The comet will be about 83 million miles away from Earth.

The mission, known as Deep Impact, aims to uncover and photograph pristine material formed billions of years ago during the creation of the universe by blasting a crater the size of a football stadium into comet Tempel 1.

Comets are composed of ice, gas and dust from the solar system's farthest and coldest regions. They often show bursts of activity, during which parts of their crusty surfaces lift off to create fan-shaped jets of dust.

They are also "carriers of basic chemical building blocks for allowing life to occur," Rick Gremmier, project manager for the Nasa mission, said on Wednesday. "We want to find out what those materials were ... and put a piece in the puzzle of how the solar system was formed."

One theory, Gremmier said, is that comets first brought water to Earth by crashing into its surface.

BLIZZARD OF PARTICLES

Deep Impact, the spacecraft that carried and will launch the impactor, will be about 310 miles away from the comet at the time of the planned collision and will have about 13 minutes after the blast to capture images and data before it weathers a blizzard of particles thrown out of the comet's nucleus.

The crash is expected to produce a hole that could range in size from that of a small house to a football stadium, depending on the density of comet's nucleus. It is not expected to change the comet's path.

There are cameras aboard both the impactor and the main craft, and the blast will also be observed by the Hubble, Spitzer and Chandra space telescopes.

There is also the chance that the mission could drift off course. The biggest challenge is the comet itself, Gremmier said, as each is different in its makeup and behaviour.

"The ultimate challenge is just trying to target a comet that is moving that fast, and also have independently the fly-by spacecraft observing the same spot as that impact," Gremmier said.

Even if the impact fails, the mission will still produce the best images to date of a comet nucleus, Gremmier said.

Earlier this week, astronomers got a preview of the orbital pyrotechnics when Tempel 1's volatile nucleus blew off a stream of dust captured by the Hubble Space Telescope.

- REUTERS and NZ Herald