Sun's just too hot to handle for Comet Ison
Agence France-Presse in Washington
Once billed as the comet of the century, Ison apparently proved no match for the sun.
Scientists said images showed the comet approaching for a slingshot around the sun on Thursday, but just a trail of dust coming out the other end.
It appears to have flown too close to the sun's surface and melted, astronomers said.
The large block of ice and rock had been expected to skim just 1.17 million kilometres above the sun's surface.
It was estimated that Ison would undergo temperatures of 2,700 degrees Celsius and lose three million tonnes of its mass per second as it made its journey around the sun.
Most astronomers predicted Ison would not survive.
Several solar observatories watched the comet during its closest approach to the sun.
It became faint while still within view of the US space agency Nasa's Solar Terrestrial Relations Observatory and the Solar and Heliospheric Observatory run jointly by the European Space Agency and Nasa.
But Nasa's Solar Dynamics Observatory lost track of it.
"It does seem that Ison probably has not survived its journey," Naval Research Laboratory comet scientist Karl Battams said after looking at space images. "I am not seeing anything that emerges from behind the solar disc and I think that could be the final nail in the coffin," he added.
Phil Plait of the Bad Astronomy blog agreed, saying he had a "strong suspicion that Ison may be an ex-comet".
Carey Lisse, a senior research scientist at Johns Hopkins Applied Physics Laboratory, compared the comet to a "loose snowball", with half or a third of its mass coming from water.
Ison was about half the size of an average comet, with an estimated maximum diameter of 1.2 kilometres.
It galvanised astronomers after its discovery by a Russian team in September last year because it traces its origins to the start of the solar system about 4.5 billion years ago.
Then, several million years ago, Ison escaped from the Oort cloud, a grouping of debris halfway between the sun and the next closest star.
Lisse called it a "dinosaur bone" of the solar system's formation, stressing the key role of comets in building planets.
The comet had shown erratic behaviour in recent days, shining brighter before suddenly losing its luminous intensity.
Some astronomers had wondered if it wasn't already in the process of disintegrating.
Additional reporting by Associated Press