Astronomers say they have seen the largest comet nucleus ever thanks to NASA's Hubble Space Telescope.
This luminous blue glow — named Comet C/2014 UN271 — was discovered by astronomers Pedro Bernardinelli and Gary Bernstein using archival images from the Cerro Tololo Inter-American Observatory in Chile.
The comet has been observed since 2010, when it was 4.8 billion kilometres away from the sun, and has been studied since.
According to NASA, its estimated diameter is approximately 85 miles or 137km across, making it larger than the ACT.
The comet's nucleus is about 50 times larger than that of most comets.
Its mass is estimated to be a staggering 450 trillion tonnes — a hundred thousand times greater than the mass of a typical comet found much closer to the Sun.
Comet is 'the tip of the iceberg'
A professor of planetary science and astronomy at the University of California, Los Angeles, David Jewitt, said in a statement: "This comet is literally the tip of the iceberg for many thousands of comets that are too faint to see in the more distant parts of the solar system.
"We've always suspected this comet had to be big because it is so bright at such a large distance. Now we confirm it is," he added.
Professor Jewitt co-authored a recent study of the comet in The Astrophysical Journal Letters, along with lead author Man-To Hui from Macau University of Science and Technology.
How was it spotted?
According to NASA, the comet is currently too far away for its nucleus to be distinguished by Hubble.
The challenge in measuring the size of the comet was distinguishing its nucleus from the huge, dusty coma enveloping it — a cloud of gases that surrounds the nucleus of a comet.
But what the Hubble data did reveal was a bright spike of light at the nucleus's location.
Dr Hui and his team made a computer model of the surrounding coma and adjusted it to fit the Hubble images.
Then, they removed the glow of the coma, revealing its starlike nucleus.
So, is it heading towards us or not?
Don't worry, we're not about to be in a real-life version of the film Don't Look Up.
The comet is travelling at 35,400 kilometres per hour from the edge of the solar system.
But NASA has assured us it will never get closer than 1.6 billion kilometres away from the Sun, which won't be until 2031.
