Spacecraft buzzes over Earth en route to meet comet

A comet-busting NASA spacecraft zipped past Earth on Monday on its way to rendezvous with another comet in an extended mission that will also see it hunt for Earth-sized planets around a cluster of stars.

The Deep Impact probe made the first of three fly-bys designed to use the planet's gravity to hurtle the spacecraft toward comet Hartley 2 for a 2010 meeting.

At its closest, the spacecraft was 16,000 kilometres above Australia.

"We're taking laps around the Sun until the comet comes," said William Blume of NASA's Jet Propulsion Laboratory.

In 2005, Deep Impact became the first spacecraft to crack open a comet by releasing a copper impactor that smashed into Tempel 1, giving scientists their first glimpse of the interior. The mothership survived and was placed in safe mode before it was tapped for an encore.

The new mission, known as Epoxi, calls for Deep Impact to meet Hartley 2 about 20 million kmfrom Earth at the time of the encounter. Deep Impact will hover 885 kmfrom the kilometre-wide surface and use its two telescopes and infrared spectrometer to map features and record gas outbursts.

On its way to the comet, Deep Impact will spend six months using one of its telescopes to search for Earth-sized planets around five nearby stars, which are known to have Jupiter-like planets orbiting them.

The extended mission, managed by JPL in Pasadena, Calif., cost $40 million, compared with the $333 million it took to collide with Tempel 1.

NASA initially wanted Deep Impact's second act to be an exploration of comet 85P/Boethin in 2008. But to scientists' surprise, a bevy of ground and space telescopes were unable to spot it this fall. Astronomers believe the comet may have shattered into specks too small to be seen from Earth.

Mission managers then asked the space agency to change course and visit Hartley 2which required a path correction and an extra two years of travel.