Hubble Space Telescope Spots Largest Comet Ever Discovered

A distant point of light captured by NASA's Hubble Space Telescope has been confirmed as the largest comet ever detected. Stretching 80 miles wide, the comet, known as C/2014 UN271 or Bernardinelli-Bernstein, is larger than the state of Rhode Island, reports Chelsea Gohd for Space.com.

The observations found that the comet is 50 times larger than the average comet core and will pass by the sun in the next decade. Details on the comet's discovery were published in The Astrophysical Journal Letters.

The colossal comet may be dashing our way from the Oort cloud at a speedy 22,000 miles per hour, per Space.com. It is expected to make its closest approach in 2031 at one billion miles away from the sun.

"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," says study author David Jewitt, an astronomer 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."

Astronomers Pedro Bernardinelli and Gary Bernstein discovered the comet in archival images from the Dark Energy Survey at the Tololo Inter-American Observatory in Chile, a statement explains. Comet Bernardinelli-Bernstein was officially observed in 2010 on accident when it was three billion miles from the sun and has since been studied by both ground and space telescopes.

At such a far distance, the comet's brightness tipped astronomers off to its large size. In January 2022, the research team confirmed its heft with five images taken by the Hubble Space Telescope. To confirm the size, researchers had to differentiate the comet's solid body, or nucleus, from its coma, the dusty cloud surrounding the object and long tail of debris trailing off of it. When a comet gets closer to the sun, its coma expands, per USA Today.

The comet's orbit is two billion miles from the sun, and its temperature is minus 348 degrees Fahrenheit. Despite the chilly temperature, it is warm enough to shed carbon monoxide from its surface, creating a cloud of dust and gas surrounding its center, per Space.com.

Hubble Confirms Largest Comet Nucleus Ever Seen

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With the five images, researchers created a computer model of the comet's coma and adjusted it to fit Hubble's images. With the model, the team removed the hazy glow of the coma to leave behind the bright nucleus. To confirm the comet's size further, the team also compared the bright nucleus to radio observations from the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, per USA Today. 

Researchers are interested in the Bernardinelli-Bernstein comet because of its origin from the Oort cloud. Comets from this region of space are thought to have formed in the inner solar system before being thrown to the edge by gravitational forces brought on by the evolution of massive planets like Jupiter and Saturn, per a statement. Astronomers hope C/2014 UN271 will reveal more details about what comets in the Oort cloud are like, USA Today reports. 

Elizabeth Gamillo | | READ MORE

Elizabeth Gamillo is a correspondent for Smithsonian and a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.