Nasa's Hubble telescope spots 'largest comet ever'

Nasa’s Hubble Space Telescope has spied the largest icy comet ever seen by astronomers.

The comet named Bernardinelli-Bernstein is estimated to be approximately 128 kilometers across, making it almost as big as Shropshire in the UK.

The nucleus of the comet is about 50 times larger than that of most known comets.

With a mass of 500 trillion tonnes, this comet is a hundred thousand times more massive than a typical comet found much closer to the Sun.

While the size of the behemoth comet travelling at 35,405 kilometers per hour could be cause for concern Nasa has assured that it will get nowhere close to planet Earth.

‘It will never get closer than 1 billion miles away from the Sun, which is slightly farther than the distance of the planet Saturn. And that won’t be until the year 2031,’ said Nasa in a statement.

Previously, the record holder for the largest known comet was C/2002 VQ94 discovered in 2002, with a nucleus estimated to be 96 kilometers across.

‘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,’ said David Jewitt, a professor of planetary science and astronomy at the University of California, Los Angeles (UCLA), and co-author of the new study in The Astrophysical Journal Letters.

‘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,’ she said.

Comet C/2014 UN271 was discovered by astronomers Pedro Bernardinelli and Gary Bernstein in archival images from the Dark Energy Survey at the Cerro Tololo Inter-American Observatory in Chile.

Its discovery was a lucky accident when astronomers chanced upon it in November 2010 when it was over 3 billion kilometers from the Sun.

Since then, it has been intensively studied by ground and space-based telescopes.

‘This is an amazing object, given how active it is when it’s still so far from the Sun,’ said the paper’s lead author Man-To Hui of the Macau University of Science and Technology, Macau.

While the researchers guessed that the comet might be pretty big the data from Hubble helped confirm it with five photos of the comet taken on January 8, 2022.

The challenge in measuring this comet was how to differentiate the solid nucleus from the huge dusty coma enveloping it as the comet was currently too far away for its nucleus to be visible in Hubble’s pictures.

Instead, the Hubble data showed a bright spike of light at the nucleus’ location which Hui and his team deciphered using a computer model to determine its actual size.

The comet which is estimated to be from a nesting ground of trillions of comets, called the Oort Cloud, has been falling toward the Sun for well over 1 million years.

What is the Oort cloud?

First hypothesized in 1950 by Dutch astronomer Jan Oort, the Oort Cloud still remains a theory because the innumerable comets that make it up are too faint and distant to be directly observed.

The Oort Cloud’s comets didn’t actually form so far from the Sun; instead, they were tossed out of the solar system billions of years ago by a gravitational ‘pinball game’ among the massive outer planets, when the orbits of Jupiter and Saturn were still evolving.

The far-flung comets only travel back toward the Sun if their distant orbits are disturbed by the gravitational tug of a passing star – like shaking apples out of a tree.

Comet Bernardinelli-Bernstein is now less than 3 billion kilometers from the Sun, where temperatures about minus 120 degrees Celsius.

The discovery provides clues to the size and distribution of comets in the Oort Cloud which is estimated to be as big as 20 times the mass of the Earth.

The more observational evidence that can be gathered, the better astronomers will understand the Oort Cloud’s role in the solar system’s evolution.

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