Hubble Confirms Comet C/2014 UN271 is an Absolute Unit, Astronomically Speaking

This diagram compares the size of the icy, solid nucleus of comet C/2014 UN271 (Bernardinelli-Bernstein) to several other comets. The majority of comet nuclei observed are smaller than Halley’s comet. They are typically a mile across or less. Comet C/2014 UN271 is currently the record-holder for big comets. And, it may be just the tip of the iceberg. There could be many more monsters out there for astronomers to identify as sky surveys improve in sensitivity. Though astronomers know this comet must be big to be detected so far out to a distance of over 2 billion miles from Earth, only the Hubble Space Telescope has the sharpness and sensitivity to make a definitive estimate of nucleus size. Credits: Illustration: NASA, ESA, Zena Levy (STScI)

It’s official. Comet C/2014 UN271 (Bernardinelli-Bernstein) has the largest nucleus ever seen in a comet. The gargantuan comet was discovered in the fall of 2021, and in January 2022, astronomers turned the Hubble Space Telescope to ascertain more details and determine the exact size.

NASA said a team of scientists has now estimated the diameter is approximately 129 km (80 miles) across, making it larger than the state of Rhode Island. The nucleus is about 50 times larger than other known comets. Its mass is estimated to be a staggering 500 trillion tons, a hundred thousand times greater than the mass of a typical comet found much closer to the Sun.

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