A piece of the early solar system that is 4 billion years old is coming this way.

Comets are some of the oldest things in the solar system. They live out in deep space. These frozen “Lego blocks” are left over from when the planet was first being built. In a game of gravitational pinball between the big planets in the outer solar system, they were thrown out of the solar system without any ceremony. The comets that were kicked out moved into the Oort Cloud, which is a huge collection of comets that surrounds the solar system and goes billions of miles into deep space.

This sequence shows how the solid icy core of Comet C/2014 UN271 (Bernardinelli-Bernstein) became separated from a large shell of dust and gas that surrounded it. On the left is a picture of the comet that was taken on January 8, 2022, by the Hubble Space Telescope’s Wide Field Camera 3. By fitting the surface brightness profile put together from the image on the left, a model of the coma was made (middle panel). This made it possible to take away the coma, revealing the point-like glow coming from the nucleus.

With the help of data from radio telescopes, astronomers were able to figure out the exact size of the nucleus. From about 2 billion miles away, that’s not an easy thing to do. Hubble can’t see the nucleus because it is so far away. It is thought to be as big as 85 miles across. Hubble’s measurements of how much it reflects light tell us how big it is. It is thought that the nucleus is about as dark as charcoal. Radio observations can be used to figure out the size of the nucleus. NASA, ESA, Man-To Hui (Macau University of Science and Technology), and David Jewitt (UCLA) deserve credit; Alyssa Pagan did the image processing (STScI)

The spectacular million-mile-long tail of a typical comet, which makes it look like a rocket, hides the fact that it is made up of a solid nucleus of ice and dust, like a dirty snowball. Hubble astronomers have found a huge comet nucleus. Most comet nuclei are only a few miles across, which means they could fit inside a small town. Comet C/2014 UN271 (Bernardinelli-Bernstein) could be as big as 85 miles across, which is more than twice as wide as the state of Rhode Island.

Astronomers Pedro Bernardinelli and Gary Bernstein found comet C/2014 UN271 by looking at old pictures from the Dark Energy Survey at the Cerro Tololo Inter-American Observatory in Chile. It was first noticed by accident in 2010. Radio observations and Hubble observations in 2022 were needed to tell the difference between the solid core and the huge dusty shell that surrounded it.

The comet is now less than 2 billion miles from the Sun and will return to its home in the Oort Cloud in a few million years.

Hubble found out how big the biggest icy comet core ever found was. And, it’s big! It is about 50 times bigger than a typical comet, with a diameter of about 80 miles. It weighs 500 quadrillion tons, which is 100,000 times more than the average comet. NASA’s Goddard Space Flight Center did the work, and Paul Morris was the lead producer.

Hubble confirms it has seen the biggest comet nucleus ever.

NASA’s Hubble Space Telescope has measured the biggest icy comet nucleus that astronomers have ever seen. The diameter is estimated to be about 80 miles, which makes it bigger than the state of Rhode Island. Most comets have nuclei that are about 50 times smaller than this one. It is thought to weigh 500 trillion tons, which is a hundred thousand times more than a normal comet that is much closer to the Sun.

The huge comet C/2014 UN271 (Bernardinelli-Bernstein) is hurtling toward us from the edge of the solar system at a speed of 22,000 miles per hour. Don’t worry, though. It will never get closer to the Sun than 1 billion miles, which is just a little farther than Saturn is from the Sun. And that will not happen until 2031.

The previous record was held by comet C/2002 VQ94, which is thought to have a nucleus that is 60 miles across. It was found by the LINEAR (Lincoln Near-Earth Asteroid Research) project in 2002.

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, said, “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 have always thought that this comet must be big because it shines so brightly from so far away. Now we know it’s true.”

Astronomers Pedro Bernardinelli and Gary Bernstein found comet C/2014 UN271 by looking at old pictures from the Dark Energy Survey at the Cerro Tololo Inter-American Observatory in Chile. It was accidentally seen for the first time in November 2010, when it was a huge 3 billion miles from the Sun, which is almost as far as Neptune is from the Sun. Since then, ground-based and space-based telescopes have looked at it a lot.

The lead author of the paper, Man-To Hui of the Macau University of Science and Technology in Taipa, Macau, said, “This is an amazing object because it is so active even though it is so far from the Sun.” “We thought the comet might be big, but we needed the best information to be sure.” So, on January 8, 2022, his team used Hubble to take five pictures of the comet.

When trying to measure this comet, it was hard to tell the solid nucleus from the huge cloud of dust that surrounded it. Hubble can’t see the comet’s nucleus right now because it is too far away. Instead, the Hubble data show that the nucleus is near a bright spike of light. Next, Hui and his team made a computer model of the coma and made changes to it so that it fit with the Hubble pictures. Then, the light from the coma was taken away, leaving only the nucleus, which looked like a star.

Hui and his team compared the brightness of the nucleus to previous radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. This information limits how big the nucleus is and how well it reflects light. The new measurements from Hubble are close to the size estimates from ALMA, but they strongly suggest that the surface of the nucleus is darker than was thought before. Jewitt said, “It’s big and as dark as coal.”

Since more than 1 million years ago, the comet has been moving toward the Sun. It is coming from the Oort Cloud, which is thought to be where trillions of comets live. The inner edge of the cloud is thought to be 2,000 to 5,000 times farther from the Sun than the Earth. Its edge could reach at least a quarter of the way to the Alpha Centauri system, which is the group of stars closest to our Sun.

The comets in the Oort Cloud didn’t form so far from the Sun. Instead, they were thrown out of the solar system by a gravitational “pinball game” between Jupiter and Saturn billions of years ago, when their orbits were still changing. Comets that are far away from the Sun and planets only move back toward them if a passing star disturbs their orbits, like shaking apples out of a tree.

Comet Bernardinelli-Bernstein has an elliptical orbit that takes 3 million years and takes it as far away from the Sun as about half a light-year. The comet is now less than 2 billion miles from the Sun and is falling nearly perpendicular to the plane of our solar system. From that far away, it’s only about -348 degrees Fahrenheit. Still, that’s warm enough for carbon monoxide to evaporate off the surface and make the dusty coma.

Comet Bernardinelli-Bernstein gives us a very important clue about how big comets are in the Oort Cloud and, by extension, about how much matter is in it. Estimates of the Oort Cloud’s mass range from 1 to 20 times the mass of Earth.

The Dutch astronomer Jan Oort first thought of the Oort Cloud in 1950, but it is still just a theory because the many comets that make up the cloud are too faint and far away to be seen directly. Ironically, this means that the largest structure in the solar system is almost impossible to see. NASA’s two Voyager spacecraft are not expected to reach the center of the Oort Cloud for another 300 years, and it could take them as long as 30,000 years to get through it.

Comets that hit Earth and can be tracked back to this nesting ground are one piece of evidence. They all come at the Sun from different directions, so the cloud must be round. These comets are pieces of the early solar system that have been frozen in time for billions of years. Models of how the solar system was made and how it changed over time support the idea that the Oort Cloud is real. Astronomers will learn more about the Oort Cloud’s role in the evolution of the solar system as they collect more evidence through deep sky surveys and observations at different wavelengths.

This diagram shows how comet C/2014 UN271 (Bernardinelli-Bernsteinicy, )’s solid nucleus compares in size to those of several other comets. Most comet nuclei that have been seen are smaller than Halley’s comet. Most of the time, they are a mile or less wide. At the moment, Comet C/2014 UN271 is the largest comet ever seen. And this might only be the tip of the iceberg. As sky surveys get more sensitive, astronomers might be able to find a lot more monsters. Astronomers know that this comet must be big if it can be seen from over 2 billion miles away, but only the Hubble Space Telescope has the sharpness and sensitivity to make a definitive estimate of the size of the nucleus. Drawing by NASA, ESA, and Zena Levy (STScI)