This Comet Is the 

Second Object We've 

Found That Came 

From Outside

 the Solar System

Guess who's interstellar? This comet. Scientists confirmed that a new object known as 2I/Borisov is definitely from outside of the solar system. It's only the second time that such an object has ever been found.

Come on in, the Solar System's Fine

Back on August 30, amateur astronomer Gennady Borisov was working at the MARGO observatory in Crimea using a telescope he built himself. He found an object that looks like a comet — which is to say, a small world of ice and rock that's bleeding off gas into space as it whizzes by the sun.

Comets can orbit the solar system from all sorts of different directions, but there's one thing that unites them: They all have a parabolic orbit. This means that they loop around in some sort of stretched-out circle that takes them from the sun to somewhere further out in the solar system and back again.

But as astronomers peered at this newly found object, they saw something strange. The path appeared to be a hyperbola — that is, a boomerang path through the solar system with no return back to the sun. It takes a long time to confirm these orbits (because you need to watch the comet for a while to predict its path), but after watching for a few weeks, we now know for sure that this thing is interstellar.

It's hard to tell just how big 2I/Borisov is, but telescopes watching it fly through our solar system have been monitoring its brightness. The measurements suggest that the comet nucleus is a few kilometers across.

New Interstellar Visitor: 2I/Borisov imaged with Gemini

IAU

Here We Go Again

This find is especially exciting for astronomers because this comet is only the second known interstellar object ever found. Almost two years ago, on October 18, 2017, astronomers saw an interstellar object make a quick pass through the solar system.

It was nicknamed 'Oumuamua and was a long, cigar-shaped object. At only 525 feet (160 meters) across, it was probably wandering the galaxy for millions or billions of years before the sun's gravity pulled it into our solar system and past Earth.

What makes our new comet find so special, though, is that it will make a much slower tour of the solar system than 'Oumuamua. This makes it easier to nab precious telescope time to learn as much as possible about 2I/Borisov before it disappears forever.

The comet is expected to make its closest approach to our sun on December 7, at just two AU away from the sun (one AU is the distance from Earth to the sun) and, coincidentally, two AU from Earth. The comet will get even brighter in the southern sky by January, before fading away into the blackness.

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