Astronomers tracking the “comet of the century” believed it had flown too close to the Sun and had broken up, but hopes have now been reignited that part of it may have survived its close encounter.
Comet Ison was due to pass within 730,000 miles of the Sun’s surface shortly after 6.30pm. It was initially declared dead after it did not re-emerge from behind the sun with the expected brightness.
“We don’t think it survived because we don’t see any new dust,” Nasa’s Solar Dynamics Laboratory said.
It was hoped that Comet Ison would provide a spectacular sight in the sky in early December. If enough of it had survived, it promised to be one of the brightest seen this century. At around 1.2 miles (2km) across, it was thought it could be just big enough to avoid being melted away by the Sun 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 1 December onwards.
Images from Nasa spacecraft showed the comet approaching for its slingshot around the sun today - but nothing emerging from the other side, suggesting it had been burned up on its journey.
However, recent pictures have suggested a brightening of what could be a small part of the comet, according to the BBC. This could continue brightening, or could simply fizzle out.
As the comet brushed past the Sun, it would have encountered temperatures of more than 2,700C (4,892F), enough to vaporise rock.
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."
But it would not be all bad news if it broke into fragments, he said, 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.