Scientists Suggest New Origin Story for ‘Oumuamua, Our Solar System’s First Interstellar Visitor

A long time ago, in a stellar system far, far away, a large cosmic object got a little too close to its star—and got shredded to bits.

Buoyed by the star’s immense gravity, the stringy, shrapnel-like remnants of this object were then flung deep into interstellar space, until one of them—a long, thin chunk shaped like a cigar—meandered into our solar system, where skygazing scientists spotted it.

Such a series of events may have been the origin story of ‘Oumuamua, the first known interstellar object to traipse into our solar system, argues the scientists behind a paper published this week in the journal Nature Astronomy. Spotted in October 2017, this odd, foreign object dazzled the world’s astronomers, who have been working to uncover its cosmic roots ever since.

Apart from being the first known object hailing from another star system, ‘Oumuamua attracted immense attention for a slew of other unusual properties, reports Nadia Drake for National Geographic. Its apparent elongated shape resembled nothing in our own solar system, and its movements couldn’t be explained by gravity alone. And while some of ‘Oumuamua’s behaviors resembled those of typical comets, its surface looked rocky and dry, like an asteroid, and lacked the usual shroud of gas and dust, or coma, that comets normally give off.

These features made ‘Oumuamua difficult to categorize, and its origin even tougher to pinpoint, study author Yun Zhang, a researcher at the Côte d’Azur Observatory in France, tells National Geographic.

So Zhang and her colleagues attempted to retrace the mysterious object’s path through space and time with a series of computer simulations until they finally found one that fit. Their candidate scenario begins in another stellar system a bit like our own, with large, planet-like objects orbiting a central star. In this foreign cosmic neighborhood, however, objects that come within about 220,000 miles of their star can succumb to its gravity and get literally ripped apart—a known process called tidal disruption.

This theoretical star’s forces are so strong that they can distort the shape of the doomed object and the pieces fragmenting off it, the team’s simulation showed, elongating some into thin, cigar-like wafers. The violence of the interaction would then hurl the malformed hunks out of the star’s vicinity and into interstellar space, as they rapidly cool and solidify into their final shape.

Though the simulation proposes just one possibility for ‘Oumuamua’s birth, it does produce an object resembling the oblong object, Zhang tells Nicola Davis at the Guardian.

“Nature doesn’t make a lot of shard-like objects,” Greg Laughlin, an astronomer at Yale University who wasn’t involved in the study, tells National Geographic. “So the fact that tidal disruption does naturally do that makes it a very compelling idea to explore, and they’ve done a very complete and careful job of exploring that option.”

The simulation may also help explain ‘Oumuamua’s puzzling movements near our sun. When comets—balls of ice and dust—begin to warm, they’ll begin to shed water vapor and other gases, which act as propellants to speed the objects up. This was never observed directly with ‘Oumuamua—perhaps because all of those reactions were happening beneath the surface, Zhang and her colleagues argue.

The approach of ‘Oumuamua’s parent body to its star might have purged much of the ice from its surface. But water buried deep in ‘Oumuamua’s interior might have survived the trip to our solar system. Warmed by the sun, these substances may have then been ejected as gas, jetting ‘Oumuamua forward at faster-than-expected speeds. According to the Guardian, this scenario is especially likely if the original star that created ‘Oumuamua was smaller than our sun.

Avi Loeb, an astronomer at Harvard University who wasn’t involved in the study, isn’t yet convinced. Tidal disruptions are thought to be rare events, making it unlikely that the product of one could have found its way to us, he tells Christopher Crockett at Science News.

But already, ‘Oumuamua has been succeeded by a second interstellar invader—the comet 2I/Borisov—and researchers think many more will soon be detected. Perhaps we’ll soon find out if ‘Oumuamua was truly a total cosmic fluke.

Katherine J. Wu | | READ MORE

Katherine J. Wu is a Boston-based science journalist and Story Collider senior producer whose work has appeared in National Geographic, Undark magazine, Popular Science and more. She holds a Ph.D. in Microbiology and Immunobiology from Harvard University, and was Smithsonian magazine's 2018 AAAS Mass Media Fellow.