A big visitor from the fringes of the solar system is headed for its closest-ever encounter with the Sun. It won’t reach that point for another nine years. And even then, it’ll be a long way out. But it should be bright enough to allow astronomers to learn a lot about it.

Comet Bernardinelli-Bernstein was discovered in 2014.

When astronomers first saw it, the comet was as far from the Sun as Neptune, the most-remote major planet. For it to be visible from that range, it must be unusually bright — which means unusually big. Astronomers aren’t quite sure how big, but it’s at least several dozen miles wide — compared to only a few miles for most comets.

The comet came from the Oort Cloud — a shell of icy bodies far from the Sun. In fact, it may be the biggest Oort Cloud comet yet seen. It probably formed closer to the Sun, then was hurled far away by the gravity of one of the giant planets.

The comet approaches the Sun every few million years. It appears to get a little closer with each visit. This time, it’ll pass a billion miles from the Sun — more than 10 times Earth’s distance.

Because it’s stayed so far away, Bernardinelli-Bernstein probably hasn’t changed much since it formed, billions of years ago. So it may reveal details about conditions when Earth and the other planets were born — details from a visitor that won’t be seen again for millions of years.
 

Script by Damond Benningfield

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