Comet the day... fireball due to pass close (1.6 million km) to the sun

It’s crunch time for a comet from the fringes of the solar system as it hurtles toward a close encounter with the sizzling sun.

Comet Ison is expected to get closest to the sun at 6.37pm Irish time today.

At that point it will be only about 1.6 million away from the sun’s surface.

Scientists say it probably won't be visible from Earth except via a fleet of Nasa telescopes and spacecraft.

But if Ison survives — and it will be a few hours before that’s known — and returns past Earth, astronomers say it should be easily visible in the northern hemisphere early next month, just before sunrise and after sunset.

The comet left the outer edge of the solar system more than 5.5 million years ago will pass close by the sun today , becoming visible in Earth’s skies in the next week or two - if it survives.

"There are three possibilities when this comet rounds the sun," Donald Yeomans, manager of NASA's Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, California, said in an interview posted on NASA's website.

"It could be tough enough to survive the passage of the sun and be a fairly bright, naked-eye object," he said. The second possibility is that the sun's gravity could rip the comet apart, creating several big chunks. "As long as there are pieces there, we'll see something," Carey Lisse, senior research scientist at Johns Hopkins Applied Physics Laboratory in Laurel, Md., told reporters on a conference call on Tuesday. The third option: If the comet is very weak, it could break up into a cloud of dust and be a complete bust for viewing.

"This comet is giving us quite a ride. It's going to be hard to predict exactly what's going on," Mr Lisse said. "As a betting man, I think it's not going to survive solar passage," he added.

Reuters/AP