Skip to Content

That comet from outside our solar system is giving off gas as it zips past us

October 1, 2019
Artist's impression of a cometary nucleus.
Artist's impression of a cometary nucleus.
Artist's impression of a cometary nucleus.ESA

Comet 21/Borisov, the second recorded interstellar visitor to the solar system, is tumbling through space with gas molecules. While that's not surprising, it's the first time we've been able to study an interstellar object as it passes through our solar system in this way.

So what?: Since discovering it just a few weeks ago, scientists have strongly suspected 21/Borisov was, well, a comet. Previously known as gb00234 and C/2019 Q4 (Borisov), the object was flaunting a large tail that was nearly 6.2 miles long. Subsequent observations confirmed the presence of outgassing matter as well as a hazy cometary coma. 

So it comes as little surprise that 21/Borisov is gassy. Astronomers using the William Herschel Telescope in the Canary Islands in Spain report detections of hydrogen cyanide molecules—toxic to humans, but a pretty common compound for comets. That gas is shaving off the comet at about 100 grams per second, which is also really common for comets this far from the sun. Through other observations of the dust and gas, the team also believes the comet is about 4.6 billion years old, and its nucleus is between 0.9 and 4.1 miles wide. 

Boring or not?: One of the strangest things about 21/Borisov is how mundane it seems. Its only notable feature so far is that it’s from outside the solar system. 

From another perspective, however, 21/Borisov is a sign that perhaps there isn’t a whole lot of variation between different star systems across the galaxy, and that they possess mostly the same types of building blocks. 

What’s next: What is exciting about 21/Borisov is that we have many more months to study it in depth. There’s hope we might be able to determine what star system it hails from, whether it possesses rarer materials, and exactly why it’s heading in our direction. The most probable explanation is that a massive planet-like object exerted enough gravity to fling 21/Borisov out of its original system like a discarded toy. Right now, some astronomers believe the star system Kruger 60, 13 light-years away, is a plausible candidate.

Keep Reading

Most Popular

transplant surgery
transplant surgery

The gene-edited pig heart given to a dying patient was infected with a pig virus

The first transplant of a genetically-modified pig heart into a human may have ended prematurely because of a well-known—and avoidable—risk.

open sourcing language models concept
open sourcing language models concept

Meta has built a massive new language AI—and it’s giving it away for free

Facebook’s parent company is inviting researchers to pore over and pick apart the flaws in its version of GPT-3

Muhammad bin Salman funds anti-aging research
Muhammad bin Salman funds anti-aging research

Saudi Arabia plans to spend $1 billion a year discovering treatments to slow aging

The oil kingdom fears that its population is aging at an accelerated rate and hopes to test drugs to reverse the problem. First up might be the diabetes drug metformin.

images created by Google Imagen
images created by Google Imagen

The dark secret behind those cute AI-generated animal images

Google Brain has revealed its own image-making AI, called Imagen. But don't expect to see anything that isn't wholesome.

Stay connected

Illustration by Rose WongIllustration by Rose Wong

Get the latest updates from
MIT Technology Review

Discover special offers, top stories, upcoming events, and more.

Thank you for submitting your email!

Explore more newsletters

It looks like something went wrong.

We’re having trouble saving your preferences. Try refreshing this page and updating them one more time. If you continue to get this message, reach out to us at with a list of newsletters you’d like to receive.