- Astronomers think they've detected an interstellar object approaching our solar system.
- Called "C/2019 Q4" (formerly "gb00234"), the object appears to be following a path originating from outside the solar system. It may pass near Mars in October.
- This would be only the second interstellar object ever observed in our solar system. The first such visitor, 'Oumuamua, took scientists by surprise in 2017. This time, they're getting ready to watch C/2019 Q4 with "everything" they can, one astronomer said.
- If C/2019 Q4 is indeed interstellar, scientists should be able to study the object until it grows too dim to see in early 2021.
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Astronomers may have spotted the second object ever to visit our solar system from another star system. The object may even fly near Mars in October.
Right now, the chances are much higher that the object, known as comet "C/2019 Q4 (Borisov)" (or "gb00234"), is interstellar, rather than a rock from within the solar system. But scientists are not yet entirely certain.
The first such interstellar object ever detected, the mysterious and cigar-shaped 'Oumuamua (which a few scientists controversially argued may be alien in origin), zoomed through our solar system in 2017.
An amateur astronomer in Crimea, Gennady Borisov, first spotted C/2019 Q4 in the sky on August 30. It hasn't yet entered our solar system, but astronomers have been collecting data in hopes of plotting the object's path through space and figuring out where it came from.
"It's so exciting, we're basically looking away from all of our other projects right now," Olivier Hainaut, an astronomer with the European Southern Observatory, told Business Insider. Hainaut was part of a global team of astronomers that studied 'Oumuamua as it passed through the solar system two years ago.
"The main difference from 'Oumuamua and this one is that we got it a long, long time in advance, " he added. "Now astronomers are much more prepared."
Why this newly discovered comet is likely from another star system
Canada-France-Hawaii TelescopeA telescope system at NASA's Jet Propulsion Laboratory, called Scout, automatically flagged C/2019 Q4 as a potential interstellar object. Though the comet's origin has not yet been confirmed, it's traveling at 93,000 miles per hour and is expected to cross our solar system's orbital plane on October 26.
"The high velocity indicates not only that the object likely originated from outside our solar system, but also that it will leave and head back to interstellar space," Davide Farnocchia, who studies near-Earth objects at NASA, said in a press release.
The object's core is between 1.2 and 10 miles (2 and 16 kilometers) in diameter. It's expected to pass through our solar system outside Mars' orbit and get no closer to Earth than 190 million miles (300 million kilometers).
Early images suggest C/2019 Q4 is followed by a small tail or halo of dust. That's a distinct trait of comets — they hold ice that gets heated up by nearby stars, leading them to shoot out gas and grit into space. The dust could make C/2019 Q4 simpler to track than 'Oumuamua, since dust brightly reflects sunlight.
That reflected light could also make it easier for scientists to study the object's composition, since telescope instruments can "taste" light to look for chemical signatures.
"Here we have something that was born around another star and traveling toward us," Hainaut said. "It's the next best thing to sending a probe to a different solar system."
Astronomers are preparing to watch the object with as many telescopes as possible
Astronomers around the globe are grabbing every telescope available to plot C/2019 Q4's path through space. The goal: see whether the object has an orbit that's elliptical (oval-shaped and around the sun) or hyperbolic (checkmark-shaped, and on an open-ended trajectory).
It seems much more likely that its path is hyperbolic, though astronomers say more observations are required to know for sure. In particular, they're trying to ascertain C/2019 Q4's eccentricity, or how extreme its orbit is.
"The error indicates it's still possible that's within the solar system," Hainaut said. "But that error is decreasing as we get more and more data, and the eccentricity is looking interstellar."
The object's seemingly high velocity and comet-like shroud of dust also tilt the scales toward interstellar, Hainaut added.
"It could be a few days or a few weeks before we have enough data to definitively say. But even with the very best data, we may need more," he said. "It's frustrating."
When 'Oumuamua sped past Earth at a distance of just 15 million miles in October 2017, astronomers had no idea it was coming.
"We had to scramble for telescope time," Hainaut said. "This time, we're ready."
Astronomers will be able to study C/2019 Q4 for at least a year.
"The object will peak in brightness in mid-December and continue to be observable with moderate-size telescopes until April 2020," Farnocchia said. "After that, it will only be observable with larger professional telescopes through October 2020."
Hainaut and his colleagues have some smaller telescopes queued up for observations, but he said he'd like to use "everything" to observe C/2019 Q4. His team is trying to get time on the "big guys," including the Very Large Telescope in Chile, the Keck Observatory, and the Gemini telescope in Hawaii.
He said at least one colleague and likely other astronomers are working on a proposal to have the Hubble Space Telescope take a look. Others are seeking to use NASA's two infrared space telescopes: Spitzer and the Wide-field Infrared Survey Explorer, or WISE.
But scientists remain cautious about C/2019 Q4's identity
ESA/Hubble; NASA; ESO; M. Kornmesser
Many astronomers are excited about C/2019 Q4, but more work has to be done to confirm it's truly interstellar.
Bannister noted that with such limited observations, an object could appear to have a rare interstellar orbit but later turn out to have an orbit within our solar system.
"Sometimes, we just have to wait for the motion of the heavens. And make...more observations," she added.
Currently, those observations aren't easy, Hainaut said. C/2019 Q4's position in the night sky places it close to the sun, giving astronomers a very limited window of time before dawn to study it.
"It's hard to see, but we have the best guys doing astrometry, trying to measure its position in the sky," he said. "It could be a few days or a few weeks before we have enough data to definitively say."
If C/2019 Q4 does turn out to be a second interstellar object, that would bode well for a mission Hainaut is proposing to send robotic probes into space to intercept future objects like this.
"One of the main issues is: How many of these are there? If we detect one every century, it's hard to plan a mission to intercept one," he said.
On the other hand, if these objects come every couple of years, astronomers might even be able to get choosy about which object to intercept.
"This suggests we can afford to wait one or two or three years to get the right one, and maybe not the first one we spot after organizing a mission," Hainaut said.
This story has been updated with new information. It was originally published on September 12, 2019.