It's being called the comet of the century but will we actually get to see it?
It was expected that Comet Ison could provide one of the most fantastic light shows ever next month on its journey past Earth.
But now there's worries it might not survive temperatures of more than 2,000C as it passes the Sun.
Astronomers monitoring Ison say they should know in the next 24 hours if the comet survives its brush with our star.
Prof Tim O'Brien, associate director of the UK's Jodrell Bank Observatory, said: "It's like throwing a snowball into fire. It's going to be tough for it to survive."
"But luckily, it's a big object and it moves fast, so it won't spend too much time close to the Sun. There is a lot of uncertainty."
- Discovered on 21 September 2012 by Vitali Nevski and Artyom Novichonok
- A so-called "sungrazer", it approaches our star at a distance of just 1.2 million km from the surface
- Ison brushes past the Sun on 28 November; the heat at in the area at the edge of the sun is expected to exceed 2,000C
- The encounter could cause Ison to break up completely, but if it survives, the comet could put on a bright display in the sky during December