Interstellar visitor is reddish, new study finds

In a new study published in Nature Astronomy on Monday, astronomers are pulling back the curtain on some of the mysteries behind our solar system's first confirmed interstellar comet.

The comet, 2I/Borisov, was discovered by amateur astronomer Gennady Borisov on Aug. 30, though its orbit was unknown.

But by the end of September, the International Astronomical Union's Minor Planet Center confirmed that the comet came from beyond our solar system. 

Because Borisov is so distant — 420 million kilometres from Earth — it's difficult to determine a lot of its characteristics. However, this new study, the astronomers were able to determine a few of its interesting qualities.

Using two telescopes, the Gemini North Telescope in Mauna Kea, Hawaii, and the William Herschel Telescope in La Palma, Spain, they were able to determine that the nucleus, or core, is roughly one kilometre in diameter. 

They also identified a short tail and an extended coma, or cloud of debris that gives comets their fuzzy appearance. And they determined its colour.

"We found this colour of the comet is almost the same as other colour of the typical comets in our solar system," said co-author of the paper Piotr Guzik, an astronomer at the Astronomical Observatory at Jagiellonian University in Krakow, Poland. "It's not red like Mars … it's just a bit more red light in its spectrum than the blue light."

In another study, researchers also found that Borisov contained cyanogen, which is made up of a carbon atom and a nitrogen atom that are bonded. It is a poisonous gas to us, but commonly found in comets.

Second interstellar visitor

Borisov is the second known object to come from another star system.

The first was 1I/'Oumuamua. It's believed that it was an asteroid, however, it's also been hypothesized that it did have some activity — called outgassing — that is similar to a comet's.

While 'Oumuamua was detected on its way out of the solar system, Borisov was detected on its way in, which means astronomers will be able to study this one for some time.

"The next year is going to be extremely exciting, as we will be able to follow 2I's evolution as it zooms through our solar system," said Olivier Hainaut, an astronomer at the European Southern Observatory, in a statement. "In comparison, we had only a few weeks to study 'Oumuamua before it became too faint."

So far, the Borisov findings suggest it isn't very different from our own local comets, something that Guzik believes could shed light on exoplanets, which orbit other stars.

"Such objects are just part of other planetary systems. It was not until, I guess, around 1990 that we found the first planet systems around other stars, and now part of such a system is here," Guzik said. "So we can investigate some material that left some planetary system and compare it to what we see here and probably learn something about the formation of other planetary systems."

Though the recent study found cyanogen, Guzik said that he's hopeful that, as the comet gets nearer the sun, astronomers will discover more about its composition.

"It will be very interesting to find out more, especially what's driving its activity," he said.

Borisov will reach perihelion — its closest approach to the sun — on Dec. 7, when it will be roughly 300 million kilometres away. 

Guzik also hopes that, eventually, astronomers will be able to determine its home star system.

"It would be really nice to know where it originated," Guzik said. "If we could point to the star and say, 'This is the star.'"