Sun-grazing comet 'likely broke up'

Scientists say it appears a comet from the fringes of the solar system didn't survive its close encounter with the sun.

Images from NASA spacecraft showed Comet ISON approaching for its slingshot around the sun, but nothing coming out on the other side.

In a Google+ hangout, US navy solar researcher Karl Battams said "ISON probably hasn't survived this journey".

Phil Plait, an astronomer who runs the Bad Astronomy blog, agreed, saying "I don't think the comet made it".

Still, he said, it wouldn't be all bad news if the 4.5-billion-year-old rock broke up into pieces, because astronomers might be able to study the pieces and learn more about comets.

The comet came within 1.6 million kilometres of the sun, which in space terms basically means grazing it.

NASA solar physicist Alex Young said it would take a few hours to confirm ISON's demise, but admitted things were not looking good.

He said the comet had been expected to show up in images from the Solar Dynamics Observatory spacecraft around 1700 GMT (0400 AEDT), but almost four hours later there was "no sign of it whatsoever".

"Maybe over the last couple of days it's been breaking up," Young said.

"The nucleus could have been gone a day or so ago."

Comet ISON was first spotted by a Russian telescope in September last year.

Some sky gazers speculated early on that it might become the comet of the century because of its brightness, although expectations dimmed as it came closer to the sun.

Made up of loosely packed ice and dirt, it was essentially a dirty snowball from the Oort cloud, an area of comets and debris on the fringes of the solar system.

Two years ago, a smaller comet, Lovejoy, grazed the sun and survived, but fell apart a couple of days later.

"That's why we expected that maybe this one would make it because it was 10 times the size," Young said.

It may be a while before there's a sun-grazer of the same size, he said.