All that could be seen was a dull smudge in space telescope images - its nucleus and tail assumed destroyed.
But recent pictures have indicated a brightening of what may be a small fragment of the comet.
Astronomers admit to being surprised and delighted, but now caution that anything could happen in the coming hours and days.
This remnant of Ison could continue to brighten, or it could simply fizzle out altogether.
"We've been following this comet for a year now and all the way it has been surprising us and confusing us," said astrophysicist Karl Battams, who operates the US space agency-funded Sungrazing Comets Project.