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NASA’s Hubble Space Telescope has determined the size of the nucleus of the largest icy comet ever seen by astronomers. Its estimated diameter is approximately 130 km wide, almost as long, for example, as the distance in a straight line between Madrid and Valladolid. The nucleus is about 50 times larger than that at the heart of most known comets, and its mass of 500 trillion tons is 100,000 times greater than that of a typical comet much closer to the Sun. .
The giant comet, C/2014 UN271 (Bernardinelli-Bernstein) is heading toward Earth at 35,400 km per hour from the edge of the solar system.
Fortunately, it will not come closer than 1,600 million km from the Sun, a little further than the distance of the planet Saturn, something that will happen in the year 2031.
The new comet “is literally the tip of the iceberg of many thousands of comets that are too faint to see in the most distant parts of the solar system,” says David Jewitt, a professor of planetary science and astronomy at the University of California, Los Angeles ( UCLA), and co-author of a new study published in The Astrophysical Journal Letters. “We’ve always suspected that this comet had to be big because it’s so bright at that distance. Now we confirm that it is », he points out. The previous record holder is Comet C/2002 VQ94, with a nucleus estimated to be 96 km in diameter.
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. It was first observed by chance in November 2010, when it was 4.8 billion km from the Sun, which is about the average distance to Neptune. Since then, it has been intensively studied by ground and space telescopes.
“This is an amazing object, given how active it is when it’s still so far from the Sun,” says Man-To Hui, of Macau University of Science and Technology, Taipa, Macau, and lead author of the study. “We guessed it could 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.
blacker than coal
The great challenge was differentiating the solid core from the huge dusty coma that enveloped it. The comet is currently too far away for Hubble to visually resolve its nucleus, so the researchers had to use a computational model of the surrounding coma to ‘separate’ it from the nucleus.
The new Hubble measurements are close to previous size estimates from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, but convincingly suggest a darker core surface than previously thought. “It’s big and blacker than coal,” says Jewitt.
The Bernardinelli-Bernstein has been falling towards the Sun for more than 1 million years. It comes as trillions of comets from the hypothetical Oort Cloud and follows a 3-million-year elliptical orbit, taking it as far from the Sun as about half a light-year. In its current situation, it is warm enough for carbon monoxide to sublime from the surface and produce the dusty coma.
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