Remember that alien comet? Scientists figured out what it’s made of

Late last year, astronomers grabbed the public’s attention when they announced they has observed an alien comet. 2I/Borisov, as it was named, had traveled to our solar system from a different planetary system, making it a very rare visitor. Now, a study of the comet using data from the Hubble Space Telescope has revealed more about its composition and origin.

There was great interest in studying the comet because of its unusual status. “With an interstellar comet passing through our own solar system, it’s like we get a sample of a planet orbiting another star showing up in our own back yard,” said John Noonan of the Lunar and Planetary Laboratory at the University of Arizona.

The researchers found that the coma of the comet, or the envelope which forms around its nucleus, had a larger amount of carbon monoxide than water ice. In fact, its ratio of carbon monoxide to water ice was three times greater than any comet we’ve seen in our solar system.

That was unexpected, as carbon monoxide shifts from ice to gas very easily, much more so than water ice, so typically you find a lot more water ice than carbon monoxide ice. It also had carbon monoxide in its inner layers that were revealed when outer layers were stripped away as it passed close to the sun.

Comet 2I/Borisov
Comet 2I/Borisov NASA , ESA , K. Meech (University of Hawaii), and D. Jewitt (UCLA)

That tells astronomers that the comet’s home system must have been unusual as well. “Borisov’s large wealth of carbon monoxide implies that it came from a planet formation region that has very different chemical properties than the disk from which our solar system formed,” astrophysicist Dennis Bodewits, the study’s lead author from Auburn University in Alabama, said in a statement.

“Because of the abundance of carbon monoxide ice that survived so close to the Sun, we think that comet Borisov comes from a much colder place and from a very different debris disk around a star than our own.”

Astronomers believe that the comet was formed a long way away from its star, which is why its carbon monoxide didn’t largely sublimate away. They also think that, because of its very high speed (it traveled through our solar system at 21 miles per second), the comet must have been kicked out of its system by a passing star or giant planet.

Studying this object is not merely a curiosity, however, as it can also teach astronomers about the evolution of different planetary systems. “We’ve been studying the composition of comets here for decades and using this information to understand how planets in our solar system formed and evolved,” said Kathleen Mandt, a planetary scientist and study author from the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.

“Measuring the composition of a comet from another planetary system was an opportunity we couldn’t miss!”

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