Thursday, November 28, 2013

Comet Ison grazes past Sun's surface

Comet Ison has made its closest approach to the Sun, passing about 1.2 million km above the star's surface.

Astronomers continue to examine the great ball of ice and dust, to see how it is coping with the encounter.

If Ison survives the immense heat and tidal forces and stays intact, it could brighten into a spectacular feature in the night sky.

An armada of special Sun-observing telescopes in space and on the ground are following Ison's progress.

Astronomers are hopeful the comet will pull though, but are realistic about the chances.

Prof Tim O'Brien, associate director of the UK's Jodrell Bank Observatory, said: 'It's like throwing a snowball into fire. It's going to be tough for it to survive.

'But luckily, it's a big object and it moves fast, so it won't spend too much time close to the Sun. There is a lot of uncertainty.'

Comet Ison came from the Oort Cloud, a mysterious, icy region at the furthest reaches of our Solar System.

Comet Ison

  • Discovered on 21 September 2012 by Vitali Nevski and Artyom Novichonok

  • A so-called 'sungrazer', it approaches our star at a distance of just 1.2 million km from the surface

  • Ison brushes past the Sun on 28 November; the heat at 'perihelion' is expected to exceed 2,000C

  • The encounter could cause Ison to break up completely, but if it survives, the comet could put on a bright display in the sky during December

It has been hurtling towards the Sun, travelling at more than a million kilometres an hour. If it pulls through, what remains of the comet will head back out to the Oort Cloud, and beyond.

Its orbital trajectory suggests this will be the one and only time the inner Solar System sees Comet Ison.

Before the encounter, astronomers estimated Ison's nucleus to be several kilometres in diameter, which would have helped it to withstand the solar assault - at closest approach, it experienced temperatures up to about 2,000C, and would have been squeezed by Sun's enormous gravitational field.

If the comet does remain largely intact, scientists say the energy of our star should excite the dust and gas in Ison's core, allowing it to blaze a trail across the heavens.