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New comet is our second interstellar visitor

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Enlarge / Comet C/2019 Q4 (Borisov). Note the fuzzy appearance and faint tail.Canada-France-Hawaii Telescope

Due to complicated gravitational interactions from planets and other bodies, it's expected that our Solar System has ejected various small bodies like comets and asteroids. Since exosolar systems are likely to do the same, it's thought that the vast distances of interstellar space are sparsely populated by these small bodies. As such, we should expect one of these objects to wander through our Solar System, an expectation that was confirmed in 2017 with the arrival of 'Oumuamua, an odd, cigar-shaped object that shot through the Solar System at an extreme angle.

Now, just two years later, we seem to have our second. Officially termed C/2019 Q4 (Borisov), the comet is approaching the inner Solar System at an angle that almost certainly indicates it didn't originate here.

Hyperbolic orbits

Right now, there's not much public information about C/2019 Q4 (Borisov). A press release from the Jet Propulsion Lab provides some basic details. Discovered on August 30, it takes its name from Gennady Borisov, who spotted it from an observatory in the Crimea. Since then, observations have firmed up its orbit, indicating that it will make its closest approach to the Sun in December, passing no closer than Mars' orbit.

The release notes that indications of its non-solar origin include a high speed and its orbit's very large angle relative to the plane of the Solar System that the planets orbit in.

To find out more about the object, we talked with University of Maryland astronomer YE Quanzhi, who studies small bodies in the Solar System. He said one of Borisov's critical contributions to this discovery was reporting the find to the International Astronomical Union's Minor Planet Center, which has portals for both asteroids and comets and a software system that can rapidly determine if an object is likely to be something we've already seen. "Astronomers anywhere in the world, if they're interested, or they study this kind of stuff, they will check this page very often and see if there is anything that they need to follow up," Quanzhi told Ars.

In this case, C/2019 Q4 (Borisov) attracted follow-up observations from the Canary Islands, China, Hawaii, and Italy, among other places. With about 100 observations, Quanzhi said that we now have a pretty good sense of C/2019 Q4 (Borisov)'s orbit. And that orbit is strange. "This first came to my attention in on Sunday morning," Quanzhi said. "Somebody posted on a mailing list saying, 'Hey, guys, this looks really weird because the orbit seems hyperbolic.'"

An eccentric visitor

Hyperbolic, he went on to explain, refers to the eccentricity of the orbit. If an orbit is perfectly circular, it would have an eccentricity of zero (the Earth's eccentricity is just above that). Eccentricity goes up as you have orbits that are more off-center and stretched out along one axis and/or more elliptical. At an eccentricity of one, an orbit is parabolic, and the object will make a single pass through the Solar System and not return.

An eccentricity of one, however, is not enough to indicate extrasolar origins. If the eccentricity is slightly above one, "we tend to think that they're still Solar System comets, but their orbit was slightly modified by the gravity of major planets."

"But if we have something that's much larger than one, that is when things start becoming interesting," Quanzhi said. "'Oumuamua, the first extrasolar object that we ever found, has an eccentricity of 1.2. And we considered that very high. And this is three. It is, you know, much more clear, much more crazy."

An animation of C/2019 Q4 (Borisov)'s path through the Solar System.
Enlarge / An animation of C/2019 Q4 (Borisov)'s path through the Solar System.

He went on to say that we're lucky to have spotted this on its approach to the Solar System. 'Oumuamua was identified when it was already on its way out, and it quickly dimmed, limiting the observations we obtained before it faded from sight. C/2019 Q4 (Borisov), in contrast, will be visible for nearly a year. In addition, astronomers are probably better prepared for its appearance. "After 'Oumuamua, there have had been a lot of discussions on how we can best respond to the next interstellar object because these objects are so rare," Quanzhi told Ars. "They carry precious information from other solar systems that we otherwise we don't havRead More – Source

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