LCO Astronomers Say Comet C/2014 UN271 Is The Largest Ever Discovered

A new comet was discovered last month by astronomers called Comet C/2014 UN271 Bernardinelli-Bernstein. The image below is a synthetic color composite image made using the Las Cumbres Observatory (LCO) one-meter telescope located in Sutherland, South Africa. The image was taken on June 22, 2021, and the comet is in roughly the center of the image with a hazy and diffuse cloud around it.

Astronomers say the diffuse cloud surrounding the brighter nucleus is the comet's coma. C/2014 UN271 was found by reprocessing four years worth of data from the Dark Energy Survey performed using the four-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile between 2013 and 2019. Astronomers determined the object had become an active comet in the three years since the Dark Energy Survey first saw it. Researchers have now found that C/2014 UN271 is the largest known comet ever discovered.

Multiple images were taken of the comet as a team worked to discover if it was active, with the first image returned being obscured by a satellite streak. However, other images were clear, and astronomers could easily tell the fuzzy dot wasn't crisp like neighboring stars signaling that it was a comet. Images also allowed researchers to determine it was still 1,800,000,000 miles from the sun, which is more than double the distance that Saturn orbits at.

C/2014 UN271 is estimated to be over 100 kilometers in diameter, which is more than three times the size of the next biggest comet nucleus known to man, which is Hale-Bopp, discovered in 1995. C/2014 UN271 isn't expected to be bright enough to be seen with the naked eye because the closest distance it will come to the sun will still be beyond the orbit of Saturn.

However, since the comet was discovered at such a vast distance from Earth, astronomers will have over a decade to study it. Its closest approach to the sun will happen in January 2031.