Comet close-ups sent by spacecraft

A NASA spacecraft survived a rendezvous with a small comet Thursday, beaming pictures back to Earth that gave scientists a rare close-up view of its centre.

Mission controllers burst into applause upon seeing images from the flyby that revealed a peanut-shaped comet belching jets of poisonous gases.

"It's hyperactive, small and feisty," said mission scientist Don Yeomans of the NASA Jet Propulsion Laboratory.

The close encounter occurred 21 million kilometres from Earth when the Deep Impact craft, hurtling through space, flew within 700 kilometres of comet Hartley 2. It's the fifth time that a comet's core has been viewed up close.

Scientists are interested in comets because they're icy leftovers from the formation of the solar system about 4.5 billion years ago. Studying them could provide clues to how Earth and the planets formed and evolved.

After the $333-million comet-buster, NASA recycled Deep Impact for a new mission to visit another comet. It was supposed to target comet Boethin in 2008, but it was nowhere to be found. Scientists theorized the comet may have broken up into small pieces.

Deep Impact was then redirected to Hartley 2.

Roughly 1.2 kilometres wide, Hartley 2 is the smallest comet to be photographed up close. On its way there, the craft spent several months scanning a cluster of nearby stars with known planets circling them.

While its latest task lacks the Hollywood drama, researchers still consider it an important mission.

'We have so little data'

"There are a lot of open questions about comets and their life cycle," said project manager Tim Larson of the NASA Jet Propulsion Laboratory, which manages the $42 million encore mission. "We have so little data that every time we have an opportunity to go near a comet, it's a chance to expand our knowledge."

Since September, Deep Impact has been stalking Hartley 2 like a paparazzo, taking images every five minutes and gathering data. Already, scientists have learned the comet releases more gas outbursts than some of its bigger counterparts.

Hartley 2 passed within 18 million kilometres of Earth on Oct. 20 — the closest it has been to our planet since its discovery in 1986.

British-born astronomer Malcolm Hartley, who discovered the comet, said he never imagined a spacecraft would get so close to his namesake find.

"When I saw the comet, it was millions and millions of kilometres away," he said. "I'm extremely excited and feel very privileged. After all, I only discovered it."