Some part of Comet Ison may have survived its close encounter with the sun, astronomers say.
It was thought the giant ball of ice and dust was destroyed by the sun's heat and gravitational pull, ending a five-and-a-half million year journey through the solar system.
But recent pictures have indicated a brightening of what may be a small fragment of the comet.
Astrophysicist Karl Battams, who operates the US space agency-funded Sungrazing Comets Project said throughout the year scientists have been following the comet it has surprised and confused them.
"It's just typical that right at the end, when we said, 'yes, it has faded out, it has died, we've lost it in the Sun', and then a couple of hours later it jsut pops right back up again," he told the BBC
How much of the once 2km-wide hunk of dirty ice could have survived is impossible to say.
Astronomers caution that anything could happen in the coming hours and days. The remnant of Ison could continue to brighten, or it could simply fizzle out altogether.