Comets are not known to be giant, but there are obviously exceptions to this rule. Researchers using the Hubble Space Telescope have spotted the largest known comet to date, C / 2014 UN271 (Bernardinelli-Bernstein). With a core of 80 miles in diameter, it easily overshadows the 60-mile circumference of the previous C / 2002 VQ94 recorder – it is about 50 times larger than a typical comet.
The comet was first discovered in 2010 by its astronomers Pedro Bernardinelli and Gary Bernstein. However, scientists have only recently confirmed the size by comparing Hubble images with a computer model of the comet (the comet’s “atmosphere” as it releases gas) and data from the large millimeter / submillimeter array Atacama. Approximately 2 billion miles from Earth, C / 2014 UN271 is too far away for Hubble to visualize the core.
And before you ask: no, there is no danger of a collision shaking the Earth. C / 2014 UN271 is in an elliptical orbit 3 million years long, which will take it no closer than 1 billion miles from the Sun or just beyond the distance of Saturn in 2031. It appears to originate from the Oort Cloud (still theoretical comet nest at least 2000 AU from the Sun) and can travel up to half a light year away. Its temperature of -348F may seem cold, but it is warm enough to cause a coma of carbon monoxide.
Confirmation of the size is not just a boast. This discovery expands humanity’s understanding of the size of comets and adds to the still small catalog of very distant comets. It can also provide more evidence for the existence of the Oort cloud and, in addition, help explain the role of the cloud in the development of the solar system.
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