Gas emissions discovered from interstellar comet


This will help scientists work out what it’s made of. Richard A Lovett reports.


An artist's concept of the interstellar comet named 2I/Borisov.

NASA/JPL

Astronomers have detected gas emissions from a comet streaking into our Solar System from interstellar space.

The comet, named 2I/Borisov, was first spotted on 30 August by a Crimean amateur astronomer, and is only the second such interstellar interloper ever to be found.

Gas emissions from it are a significant find because they allow scientists to use spectrographic methods to begin deciphering exactly what the comet is made of.

That wasn’t possible with 1I/’Oumuamua, the only other interstellar object to be caught traversing the Solar System, because ’Oumuamua was never seen to emit detectable amounts of gas.

“For the first time, we are able to accurately measure what an interstellar visitor is made of and compare it with our own Solar System,” says Alan Fitzsimmons, an astrophysicist at Queens University, Belfast, UK.

So far, the astronomers have detected only one gas being emitted by the comet, cyanogen (CN). They have also put an upper bound on the amount of another gas, diatomic carbon (C2), which would have been detectable if the comet was producing a lot of it.

What’s more, they’ve been able to measure the rate at which CN is being emitted into the comet’s tail and coma (the cloud surrounding its nucleus), as well as making estimates about the amount of dust the comet is producing.

Based on these figures and the normal rates at which comets of various sizes emit such materials, it appears that the comet’s nucleus measures somewhere between 1.4 and 6.6 kilometers in diameter, they say.

That makes it a lot bigger than ’Oumuamua, which appears to have been a cigar-shaped body with an average diameter of no more than 200 meters.

’Oumuamua was so small, in fact, that it was not detected until late in its passage through the Solar System, allowing only a two-week opportunity for detailed observation.

Borisov, on the other hand, is still on its way into the Solar System and will be visible until October 2020, Fitzsimmons’s team says in their paper, which has been submitted to the journal Astrophysical Journal Letters.

But the most interesting thing is how ordinary Borisov appears to be. “If it were not for its interstellar nature, our current data shows that 2I/Borisov would appear as a rather unremarkable comet in terms of activity and coma composition,” Fitzsimmons’ team write.

So far, only a single gas has been discovered. “But that’s still one step further in understating the composition of the ‘exocomet,’ if you want to call it that,” says Humberto Campins, a planetary scientist from Central Florida University, Orlando, who was not part of Fitzsimmons’ team.

“And it is headed closer to the Sun, so we should have an opportunity to study it in more detail.”

Contrib ricklovett.jpg?ixlib=rails 2.1
Richard A. Lovett is a Portland, Oregon-based science writer and science fiction author. He is a frequent contributor to COSMOS.
  1. https://www.nationalgeographic.com/science/2019/09/bizarre-interstellar-comet-from-another-star-system-just-spotted/
  2. https://arxiv.org/abs/1909.12144
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