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The Nearly Spherical Cow of Comets Heading Our Way

Accepted submission by fliptop at 2021-10-11 16:52:14
Science

Dubbed Bernardinelli-Bernstein [wikipedia.org], it is thousands of times more massive than an average comet. Its close approach [thedailybeast.com] is a rare chance to learn more about how Earth and its neighbors were born:

Seven years ago, a pair of scientists scouring high-resolution images of space caught fleeting glimpses of a bright round object peeking from a vast cloud of icy objects more than 2 billion miles from Earth.

As if that whole scene wasn’t exciting enough, the object appeared to be a huge comet. Thought to be between 60 and 100 miles wide, it was the biggest comet a human being had ever witnessed. And it seemed to be heading toward us, very loosely speaking.

[...]Because it’s so much bigger than other known comets—the famous Hale-Bopp comet, which itself is on the larger side, measures just 37 miles across—Bernardinelli-Bernstein possesses enough gravity to hold itself together as it lazily loops through space. It’s harder to break apart.

The comet’s extreme distance from the sun also helped preserve it. “It spends most of its time in the deep freeze of the outer solar system,” Mainzer explained. Models of the megacomet’s orbit indicate it last entered our part of the solar system around 5 million years ago and got no closer than Uranus. From that distance, the sun’s heat hardly touched it.

Mainzer says that as a result, the comet she affectionately calls “BB” probably resembles the original chemical state of the nebula of gas and dust that formed our solar system about 4.5 billion years ago.

[...]It’s highly unlikely NASA or some other space agency building a probe to intercept and collect samples from Bernardinelli-Bernstein (which is ironically what NASA is currently doing with the asteroids surrounding Jupiter).


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