Article published courtesy of NASA:
NASA’s Hubble Space Telescope has determined the size of the largest icy comet nucleus ever seen by astronomers. The estimated diameter is about 80 miles across, making it larger than the state of Rhode Island. The nucleus is about 50 times larger than that found at the core of most known comets. Its mass is estimated at 500 trillion tons, one hundred thousand times greater than the mass of a typical comet found much closer to the Sun.
This sequence shows how the nucleus of comet C/2014 UN271 (Bernardinelli-Bernstein) was isolated from a vast shell of dust and gas surrounding the solid, icy core. On the left is a photo of the comet taken by NASA’s Hubble Space Telescope Wide Field Camera 3 on January 8, 2022. A model of the coma (middle panel) was obtained by fitting the assembled surface brightness profile from the observed image on the left. This subtracted the coma, revealing the pinpoint glow from the core. Combined with data from the radio telescope, astronomers arrived at an accurate measurement of the size of the nucleus. That’s no small feat of something around 2 billion miles. Although the core is estimated to be 85 miles in diameter, it is so far away that it cannot be resolved by Hubble. Its size is derived from its reflectivity as measured by Hubble. The core is estimated to be as black as charcoal. The core area is gleaned from radio observations.
Credits: NASA, ESA, Man-To Hui (Macao University of Science and Technology), David Jewitt (UCLA); Image processing: Alyssa Pagan (STScI)
The giant comet, C/2014 UN271 (Bernardinelli-Bernstein) is hurtling in this direction at 22,000 miles per hour from the edge of the solar system. But do not worry. It will never approach closer than a billion kilometers from the Sun, which is slightly further than the distance from the planet Saturn. And it won’t be until 2031.
The previous record holder is comet C/2002 VQ94, with a core estimated to be 60 miles in diameter. It was discovered in 2002 by the Lincoln Near-Earth Asteroid Research (LINEAR) project.
“This comet is literally the tip of the iceberg for several thousand comets that are too faint to be seen in the most distant parts of the solar system,” said David Jewitt, professor of planetary sciences and astronomy at the University of California at Los Angeles. Angeles (UCLA), and co-author of the new study in Letters from the Astrophysical Journal. “We always suspected that this comet must be big because it is so bright at such a great distance. Now we confirm that it is.”
Comet C/2014 UN271 was discovered by astronomers Pedro Bernardinelli and Gary Bernstein in archival footage from the Dark Energy Survey at the Cerro Tololo Inter-American Observatory in Chile. It was first observed by chance in November 2010, when it was 3 billion kilometers from the Sun, almost the average distance to Neptune. Since then, it has been intensively studied by ground and space telescopes.
“It’s an amazing object, considering how active it is when it’s still so far from the Sun,” said the paper’s lead author, Man-To Hui, from the University of Science and Technology in China. Macau, Taipa, Macau. “We guessed the comet might be quite large, but we needed the best data to confirm that.” So his team used Hubble to take five photos of the comet on January 8, 2022.
The challenge in measuring this comet was how to distinguish the solid core from the huge dusty coma that shrouds it. The comet is currently too far away for its nucleus to be resolved visually by Hubble. Instead, the Hubble data shows a bright peak of light at the location of the nucleus. Hui and his team then created a computer model of the surrounding coma and adjusted it to fit the Hubble images. Then the coma glow was subtracted to leave behind the star-shaped core.
Hui and his team compared the brightness of the core to earlier radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. These combined data limit the core diameter and reflectivity. The new Hubble measurements are close to previous ALMA size estimates, but convincingly suggest a darker core surface than previously thought. “It’s big and it’s blacker than coal,” Jewitt said.
This diagram compares the size of the solid, icy core of comet C/2014 UN271 (Bernardinelli-Bernstein) to several other comets. The majority of observed cometary nuclei are smaller than Halley’s Comet. They are usually a mile in diameter or less. Comet C/2014 UN271 currently holds the record for large comets. And that may just be the tip of the iceberg. There could be many more monsters astronomers can identify as surveys of the sky improve in sensitivity. Although astronomers know this comet must be big to be detected so far away at a distance of more than 2 billion miles from Earth, only the Hubble Space Telescope has the sharpness and sensitivity to make a definitive estimate of the size of the comet. core.
Credits: Illustration: NASA, ESA, Zena Levy (STScI)
The comet has been falling towards the Sun for more than a million years. It comes from the hypothetical nesting place of trillions of comets, called the Oort cloud. The diffuse cloud is believed to have an inner edge at 2,000 to 5,000 times the distance between the Sun and Earth. Its outer edge could extend at least a quarter of the way to the distance of the closest stars to our Sun, the Alpha Centauri system.
Oort Cloud comets did not form so far from the Sun; instead, they were thrown out of the solar system billions of years ago by a gravitational “pinball game” among the massive outer planets, while the orbits of Jupiter and Saturn were still evolving. Distant comets only return to the Sun and planets if their distant orbits are disturbed by the gravitational tug of a passing star – like shaking apples off a tree.
Comet Bernardinelli-Bernstein follows an elliptical orbit 3 million years long, taking it about half a light-year away from the Sun. The comet is now less than 2 billion miles from the Sun, falling almost perpendicular to the plane of our solar system. At this distance, temperatures are only about minus 348 degrees Fahrenheit. Yet it’s hot enough for carbon monoxide to sublimate to the surface to produce the dusty coma.
Comet Bernardinelli-Bernstein provides an invaluable clue to the size distribution of comets in the Oort cloud and therefore to its total mass. Estimates of the mass of the Oort Cloud vary widely, reaching up to 20 times the mass of Earth.
Hypothesized for the first time in 1950 by the Dutch astronomer Jan Oort, the Oort cloud is still a theory because the countless comets that compose it are too weak and too far away to be directly observed. Ironically, this means the largest structure in the solar system is virtually invisible. It is estimated that NASA’s pair of Voyager spacecraft will not reach the inner realm of the Oort Cloud for 300 years and could take up to 30,000 years to cross.
Circumstantial evidence comes from falling comets that can be traced back to this nesting site. They approach the Sun from all directions, which means that the cloud must be spherical in shape. These comets are frozen samples of the composition of the early solar system, preserved for billions of years. The reality of the Oort cloud is reinforced by theoretical modeling of the formation and evolution of the solar system. The more observational evidence can be gathered through deep-sky surveys coupled with multi-wavelength observations, the better astronomers will understand the role of the Oort cloud in the evolution of the solar system.
Hubble has determined the size of the largest icy comet nucleus ever discovered. And, it’s big! With a diameter of about 80 miles, it is about 50 times larger than typical comets. Its mass of 500,000 billion tons is a hundred thousand times greater than the average comet.
Credits: NASA Goddard Space Flight Center; Main producer: Paul Morris
The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.