US solar physicists will be following the rare comet Ison on Thursday as it slingshots around the sun, waiting to see how much of it survives an abnormally close encounter with the star.
Ison, a big chunk of rock estimated to be 4.6 billion years old, has been speeding for 5 million years from the outer solar system toward the sun, said Alex Young of the Goddard Space Flight Centre in Maryland in a webcast posted on the NASA website.
Because it will come nearer than most comets — about 1 million kilometres — Ison is a “sun-grazing comet,” Young said.
“What makes them really exciting is that they are fossils from the early solar system,” Young said.
The NASA solar science team will host a Google+ Hangout starting about 1800 GMT on Thursday to discuss Ison’s journey through the solar system and what the public might be able to see in the coming days.
The Thursday solar near miss coincides with traditional Thanksgiving Day celebrations around the US.
Young said Ison is large enough that he expects it to survive the passage. Other experts say the ice that holds together smaller chunks of material in a comet could melt and cause Ison to disintegrate.
“Studying comets allows us to look in the past and see the conditions 4.5 billion years ago,” Young said.
Ison’s passage so near the sun will allow solar scientists to also study the sun’s atmosphere. Ison will probably not be visible to the naked eye on Thursday.
Starting Sunday, it will be visible low in the sky early in the morning and get progressively higher and earlier in the night, Young said.
By December 15, it will be roughly located near the Big Dipper. Young said it will be a “once in a lifetime” chance to view Ison. “It’s a pristine comet... and it’s not going to come back,” he said.