Sunday 24 September 2017

Stargazers disappointed as Comet Ison fails to survive encounter with the sun

Comet ISON as pictured on November 19
Comet ISON as pictured on November 19

Watchers of the heavens appeared to be facing disappointment tonight as it seemed that a comet had not survived a fiery encounter with the sun.

It was hoped that Comet Ison would provide a spectacular sight in the sky next month - but the signs were that it had been burned up on its journey.

The comet was due to graze the outer layers of the sun at 6.37pm UK time tonight, approaching as close as 730,000 miles (1,174, 821km) from the star's surface.

As it brushed past the sun, the comet would encounter temperatures of more than 2,700C (4,892F), enough to vaporise rock.

If enough of it survived, it promised to be one of the brightest seen this century, but its fate would be decided by its size. At around 1.2 miles (2km) across, it was thought it could be just big enough to avoid being melted away or turned to dust.

Even at a greatly reduced size it was hoped it could produce a glorious long tail, visible to the naked eye from the UK from December 1 onwards.

Images from Nasa spacecraft showed the comet approaching for its slingshot around the sun today - but nothing coming out on the other side.

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."

However he said it would not be all bad news if the rock broke into pieces, because astronomers might be able to study them and learn more about comets.

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

He said the comet had been expected to appear in images from the Solar Dynamics Observatory spacecraft at around 5pm British time, but almost four hours later there was "no sign of it whatsoever".

He added: "Maybe over the last couple of days it's been breaking up. The nucleus could have been gone a day or so ago."

Astronomer Dr Dan Brown, from Nottingham Trent University, said earlier: "Astronomers around the world are hoping that Ison will become an amazing sight for the naked eye in the first half of December. They are keeping a close eye on it, using some of their solar observatories in space.

"People at home can also capture a glimpse if it survives. Just look out for it half an hour before sunrise from December 1 onwards. It will be visible low in the east-south-eastern horizon.

"This close encounter with the sun also offers a unique opportunity for astronomers to analyse the composition of a comet. Comets are icy, dusty snowballs - the remains from the formation of our solar system 4.5 billion years ago.

"The long tail containing the material frozen in the comet and released through the heat of the sun offers astronomers the chance to identify different elements."

The comet was discovered last year by two amateur astronomers using Russia's International Scientific Optical Network (Ison).

It was born in the Oort cloud, a shell of scattered icy objects right at the outermost edge of the Solar System. The cloud is nearly a light year from the sun, a quarter of the distance to our nearest neighbouring star, Proxima Centauri.

Sometimes a comet is nudged out of the cloud by the gravitational tug of a passing star, and sent on a journey taking millions of years that eventually brings it into the inner Solar System.

Computer models show that Ison is one such comet. However, it is unusual in being a first-time visitor and also in a sun-grazing orbit.

Dr Brown added: "It has already been bright enough for astronomers to capture amazing pictures. However, if the comet survives its burning close encounter with the sun it may have a huge and impressively long tail with a brightness that might make it an easy to spot object even with the naked eye.

"This happened in 1965 with the comet Ikeya Seki that had an enormously long tail. But some comets, like Lovejoy three years ago, have been ripped apart during their close encounter by the sun's gravitational force.

"The magic limit for survival of the comet seems to be the size, which has to exceed two kilometres so it does not get boiled away or ripped apart by the sun. Ison is estimated to be that size, so we should all cross our fingers and await our early Christmas comet."

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