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This is the second known interstellar object after 'Oumuamua in 2017 (artist's impression shown).
Break out the party hats. Astronomers have all but confirmed that the second known interstellar object is currently whizzing through our Solar System – and unlike the first event, we’ll be able to study it in a huge amount of detail.
The object was originally given the moniker gb00234, and was discovered by an amateur astronomer called Gennady Borisov in Crimea using his own observatory called MARGO. Borisov first spotted the object on August 30 and was immediately alerted by its odd path – suggesting it was not bound to our Sun.
Subsequent analysis and observations have confirmed the object has a high eccentricity, meaning it is on a hyperbolic path that will take it in and out of our Solar System, never to return. The Minor Planet Center (MPC) at the Harvard-Smithsonian Center for Astrophysics confirmed the orbit of the object earlier today and gave it a new name in honor of its discoverer: C/2019 Q4 (Borisov).
“We were somewhat cautious as to whether it was hyperbolic or not,” says Matthew Payne from the MPC. “Over the course of the past few days, it became increasingly apparent that it looks like it has a hyperbolic trajectory.”
As mentioned this would be the second known interstellar object to enter our Solar System, since a first called ‘Oumuamua (or 1I/2017 U1) was spotted in October 2017. Both are believed to have traveled from other planetary systems to our own across the vast expanse of the galaxy over millions or even billions of years.
There are a couple of key differences this time around though. The first is that from images, we are fairly certain C/2019 (which will likely be given the label 2I/2019) is a comet about 10 kilometers across as it appears to have a visible tail, whereas ‘Oumuamua appeared to be something more sedate.
“The first one did not appear cometary, it appeared asteroidal,” says Payne. “Whereas this one definitively is cometary in nature.”
The other major difference is that ‘Oumuamua was on its way out of the Solar System when we saw it, allowing us to study it for only a matter of weeks before it became too dim to see any more. C/2019, however, is not only about six times brighter but is also making its way into the Solar System at about 30 kilometers per second, giving us a much longer period of time to study it.
“[It will stay in the Solar System] for about six months at least,” says astronomy-software developer Bill Gray, who has been closely involved in the discovery, although he notes there are still uncertainties. “We don’t know how bright it’s going to be. That’s always an issue with comets, so you’ve got that unpredictability, combined with the fact that it is interstellar. And this is the first interstellar comet we’ve seen.”
At its closest, the object is expected to reach about 1.8 times the Earth-Sun distance (1.8 AU, or astronomical units) on December 10 (it was discovered at a distance of three AU). "That's the closest approach, which will be in December of this year," says physicist Marshall Eubanks from Space Initiatives and the Institute for Interstellar Studies in the US. “And the closest approach to the Sun is about the same time."
Now the race will be on to train any and all telescopes possible, from the Hubble Space Telescope to backyard observatories, on this fascinating object as it pays us a prolonged visit. Its cometary nature means we could study its composition and origins in great detail, giving us a better insight into an alien planetary system than ever before. 'Oumuamua was simply too inactive, and passed too quickly, for us to learn anywhere near as much.
The discovery will be music to the ears of many who have been expecting more of these objects, too. Some estimates suggest that at least one interstellar object should be in our Solar System at any given time, while the upcoming Large Synoptic Survey Telescope (LSST) plans to find many more of these objects. The European Space Agency (ESA), meanwhile, may even send a spacecraft to an interstellar visitor in the future.
C/2019’s status as an interstellar object will still need to be completely verified to be sure it really is a visitor from afar. But many astronomers are already certain, and are beginning to dream of what will come over the next six months. “Personally, as soon as I saw that the incoming orbit was close to the galactic plane, I was sure it was interstellar,” says Eubanks.