Largest comet ever seen is longer than Connecticut - study

The comet, C/2014 UN271 (Bernardinelli-Bernstein), is over 128.7 kilometers in diameter and has a mass of around 500 trillion tons. It won't hit us, but it will help us understand the Oort Cloud.

 This illustration shows the distant comet C/2014 UN271 (Bernardinelli-Bernstein) as it might look in the outer Solar System.  (photo credit: Wikimedia Commons)
This illustration shows the distant comet C/2014 UN271 (Bernardinelli-Bernstein) as it might look in the outer Solar System.
(photo credit: Wikimedia Commons)

The largest comet ever seen is barreling towards Earth at rapid speeds, but while there is no chance it will hit us, it does shed light on one of the most mysterious structures in the solar system, scientists noted in a new academic study.

The comet, identified as C/2014 UN271 (Bernardinelli-Bernstein), is heading toward the Earth's direction at a speed of around 35,400 kilometers per hour. Further, it is absolutely enormous, with its nucleus – the central part of the comet – is estimated by the Hubble Space Telescope to be over 128.7 kilometers in diameter with a mass of around 500 trillion tons. For comparison, the US state of Rhode Island is only around 59-60 kilometers wide and the state of Connecticut is 113 kilometers long, meaning this comet is larger than two US states, albeit not stacked together. Regarding the mass, it is so astronomical that a contemporary terrestrial comparison is essentially impossible.

The size of this massive comet absolutely smashes the previous record holder, C/2002 VQ94, but according to the study, published in the peer-reviewed academic periodical The Astrophysical Journal Letters, this is just the tip of the iceberg – literally.

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 study co-author David Jewitt, a professor of planetary science and astronomy at the University of California, Los Angeles (UCLA). "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."

What is a comet?

Comets are one of the two most iconic objects found floating around space, alongside asteroids.

Unlike asteroids, however, which are large rocks, comets are mostly composed of ice and dust, along with some rocky particles. This, in turn, gives them an atmosphere of sorts around the nucleus, though extinct comets lack this and look like small asteroids

When a comet flies close to the Sun, the heat causes it to warm and release gases. This subsequently forms a large bright trail known as coma and sometimes even a tail. These can help make the comets much brighter – which, in turn, makes them much easier to spot, even with the naked eye. 

However, the fact that comets need to be closer to the Sun to be so bright means it is therefore strange that C/2014 UN271 could be seen to be so active at such a distance – and this is something the researchers noted.

"This is an amazing object, given how active it is when it's still so far from the Sun," explained the paper's lead author Man-To Hui of the Macau University of Science and Technology, Taipa, Macau. "We guessed the comet might be pretty big, but we needed the best data to confirm this." 

This wasn't easy, however. WIth how far it was, it wasn't clear where the nucleus ended and the coma began, and it's still too far away to tell with Hubble. But by analyzing a bright spike of light in the nucleus noted by Hubble's data and using a computer model to properly fit it, the team was able to figure out the parameters of the nucleus. 

In conclusion, it's very big and very dark, with Jewitt describing it as "blacker than coal."

What is the Oort Cloud?

This particular comet is believed to have come from the Oort Cloud, a theorized area at the outer edge of the solar system that is essentially a spherical shell made up of icy pieces of debris. It is these pieces of debris that, when they fall out of the cloud, head towards the Sun and become comets.

This cloud is very mysterious, however. Its exact size and mass is a mystery, and even its entire existence is merely theorized since its many comets are too far for observation, meaning this astronomically large structure is essentially invisible. 

NASA's Voyager spacecrafts will eventually reach the Oort Clouds, but that won't be for another 300 years, and passing through it entirely could take 30,000 years.

But C/2014 UN271 actually sheds considerable light on what we now know about the Oort Cloud because it is now a frame of reference for the sizes of the comets inside this structure, which in turn can lead to a total estimated mass of the Oort Cloud itself.

When will the comet come?

The gargantuan comet is flying in the direction of the Sun but not only will it not be here any time soon, it also won't even be anywhere close to the Earth when it does arrive.

According to the study, C/2014 UN271 won't arrive until 2031. Even when it does, it will be, at minimum, 1.6 billion kilometers away from the Sun. For comparison, that's even farther than the distance between the Sun and Saturn.

So rest easy, Earth is in no danger, but C/2014 UN271 can help scientists understand more about the universe around us. And, if we're lucky and have a strong enough telescope, there's a chance that come 2031, we'll have another comet to watch in the sky.