The biggest comet ever spotted from the outer solar system is 137 kilometres wide


Astronomers have calculated the size of a ‘mega comet’ originating in the Oort Cloud (biggest comet ever), a grouping of ice debris that surrounds our solar system.

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Comets are cosmic snowballs of frozen gases, rock, and dust that orbit the Sun. When frozen, they are the size of a small town. When a comet’s orbit brings it close to the Sun, it heats up and spews dust and gases into a giant glowing head larger than most planets. The dust and gases form a tail that stretches away from the Sun for millions of miles. There are likely billions of comets orbiting our Sun in the Kuiper Belt and even more distant Oort Cloud.

Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years. Short-period comets originate in the Kuiper belt or its associated scattered disc, which lie beyond the orbit of Neptune. Long-period comets are thought to originate in the Oort cloud, a spherical cloud of icy bodies extending from outside the Kuiper belt to halfway to the nearest star.

Comet C/2014 UN271 (Bernardinelli-Bernstein) was discovered beyond Uranus’ orbit in June 2021, according to astronomers. Its brightness suggested it was a massive object emanating from the Oort Cloud, a cloud of ice bodies that orbits our solar system. It measured from 100 to 370 kilometres in size.

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