Comet 85 miles wide is officially the largest comet ever observed

The new record, report­ed on the preprint web­site arX­iv and now accept­ed for pub­li­ca­tion in the jour­nal Astron­o­my and Astro­physics Let­ters, moves comet Hale-Bopp from the top spot. Hale-Bopp was dis­cov­ered in 1995 and became vis­i­ble to the naked eye in 1996; it was about 46 miles (74 kilo­me­ters) in diam­e­ter. Bernar­dinel­li-Bern­stein, also known as comet 2014 UN271, has now been cal­cu­lat­ed to be about 85 miles (137 kilo­me­ters) in diameter.

Comet Bernar­dinel­li-Bern­stein is named after its dis­cov­er­ers, Uni­ver­si­ty of Penn­syl­va­nia cos­mol­o­gist Gary Bern­stein and Uni­ver­si­ty of Wash­ing­ton post­doc­tor­al researcher Pedro Bernar­dinel­li, who first spot­ted the comet in the Dark Ener­gy Sur­vey data set.

The images show­ing the comet are from 2014, which is why this year is includ­ed in the comet’s offi­cial sci­en­tif­ic des­ig­na­tion. Bernar­dinel­li and Berstein noticed that the small dot was mov­ing as they stud­ied images from sub­se­quent years.

At that time, the comet was too far away for researchers to have a good idea of its size, although they could tell it was prob­a­bly quite large.

The comet orig­i­nat­ed in the Oort cloud, a cloud of chunks of ice and rock hov­er­ing at the edge of the solar sys­tem. Its orbit takes it to with­in a light year of the sun — and takes 5.5 mil­lion years to complete.

The comet is cur­rent­ly head­ing towards the inte­ri­or of the solar sys­tem. It will come close to Earth in 2031, but not too close for com­fort: the comet will stay just out­side Sat­urn’s orbit, Live Sci­ence reported.

The new research was led by Emmanuel Lel­louch, an astronomer at Paris Obser­va­to­ry, and used data from the Ata­ca­ma Large Mil­lime­ter Array in South Amer­i­ca, tak­en in August 2021 when the comet was 19.6 AU away. (An AU is the dis­tance between Earth and the sun and trans­lates to about 93 mil­lion miles, or 150 mil­lion kilometers).

The researchers stud­ied microwave radi­a­tion from the comet’s mass. From these reflect­ed light wave­lengths, the team was able to deduce the size of the comet. This is the longest dis­tance at which this type of mea­sure­ment has been done before, the researchers wrote in their new paper.

It’s excit­ing to get a mea­sure­ment while the comet is still so far away, the researchers added, because Bernar­dinel­li-Bern­stein will like­ly shrink con­sid­er­ably as it approach­es Earth. As the comet gets clos­er to the sun, its tail of dust and gas expands and its main body melts and shrinks.

The comet will not be vis­i­ble to the naked eye, as Hale-Bopp was at its clos­est approach, but sci­en­tists expect to learn a lot about the objects in the vis­i­tor’s Oort cloud.

Large tele­scopes like the Ata­ca­ma Array will allow sci­en­tists to learn more about the comet’s chem­i­cal com­po­si­tion as it pass­es by, Lel­louch and col­leagues wrote. They should also soon learn more about the comet’s tem­per­a­ture, rota­tion and shape.

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