The Hubble Space Telescope has discovered a small armada of mini-comets left behind by the disintegration of Comet Linear.

My first thought was Hubble Space Telescope does it again!

Hal Weaver

Comet Linear fragmented as it passed close to the Sun on 27 July. Some astronomers thought it had completely fizzled out.

But observers at the Space Telescope Science Institute (STScI) in Baltimore, US, reprogrammed the Hubble telescope to search for any remaining pieces of the comet that might have hung on.

They were rewarded with the sight of a swarm of small fragments. However, these are expected to disappear over the course of the next few weeks.

Explosions and jets

Johns Hopkins University astronomer Hal Weaver said he was stunned when he saw the Hubble image: "My first thought was Hubble Space Telescope does it again! This is amazing, very exciting, very neat."

Comets have been known to break apart before but this is the first time astronomers have had a close-up view of the dismantling of a comet by the Sun's heat.

The central part of a comet, its nucleus, is a conglomerate of dust and ice. As it nears the Sun, heat causes the ices to turn to gas in explosions and jets.

Solar radiation and particles then blow the debris away from the Sun forming the comet's tail.

Detailed observations of the break-up of a comet are important because they tell scientists how the body was put together in the first place.

'Size of a mountain'

On Weaver's screen were at least a half dozen mini-comets with tails. They were clustered at the head of an elongated stream of dust. An isolated brighter piece in front of the cluster may be the parent nucleus for the smaller fragments.

"Actually, I would have been more amazed if Hubble saw no pieces," said co-investigator Carey Lisse. "The comet's break-up was too violent and fast for it to completely vaporise. How do you pulverise something the size of a mountain?"

Some astronomers believe this was Comet Linear's first visit to the inner Solar System. It was born one light-year away (10 trillion km or 6 trillion miles) in a region called the Oort cloud.

Other astronomers believe that Linear may have been a fragile piece that broke off from a larger comet that visited us more than 10 million years ago.