A new “alien spacecraft” paper poses a challenge for astrophysicists

An artist’s rendition of the first interstellar asteroid discovered in our solar system.
An artist’s rendition of the first interstellar asteroid discovered in our solar system.
Image: ESO/M. Kornmesser
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About a year ago, scientists using the Pan-STARRS1 telescope in Hawaii noticed what seemed to be a peculiar asteroid passing through our solar system. It was speeding ahead so quickly, at roughly 64,000 kilometers per hour (40,000 mph), that they realized that it must be from somewhere else entirely.

They dubbed the asteroid ‘Oumuamua, the Hawaiian word for “messenger from afar arriving first.” They thought it could be a potential host of extraterrestrial life. But the current telescope technology available found nothing of note on the asteroid.

Still, there were some strange things about ‘Oumuamua: Normally, scientists would assume that an interstellar object would be a comet. But comets have clouds of gas surrounding them, and ‘Oumuamua seemed to have none. Second, it seemed to be getting faster—and not through the gravitational pull of other objects, as researchers would expect.

The mystery prompted Shmuel Bialy, a postdoctoral fellow at the Harvard-Smithsonian Center for Astrophysics, and Avi Loeb, another Harvard astronomer, to attempt to figure out what was going on with ‘Oumuamua. One possibility was that the asteroid was sailing on solar radiation. “It’s already a known phenomenon that when radiation hits an object, it can cause acceleration,” says Bialy. “It’s just like wind hitting a sail,” except instead of wind, it’s light propelling the object forward.

On Nov. 1, Bialy and Loeb released a pre-print of a paper, to be published in The Astrophysical Journal Letters later this month, exploring the solar-radiation hypothesis. Their conclusion: If  ‘Oumuamua was being propelled by solar radiation, it would have to be less than a millimeter thick, and hundreds of meters long. That shape would likely have a hard time withstanding the dust, plasma, and extreme temperatures of the interstellar medium. And even if the shape could hold up against interstellar weathering, it would still be a form unlike anything that exists on Earth, or anything that could exist under the currently-understood laws of astrophysics. 

In other words? Something weird is going on with ‘Oumuamua. Bialy and Loeb concluded maybe it came from an “artificial origin,” implying that it was made by something other than natural formation. Or, as they write, “a more exotic scenario is that ‘Oumuamua may be a fully operational probe sent intentionally to Earth vicinity by an alien civilization.”

News outlets have since gone to town with headlines proclaiming scientists at a prominent institution were suggesting aliens as a real possibility. Many outlets also cited dissenting astrophysicists. “I am distinctly unconvinced and honestly think the study is rather flawed,” Alan Jackson, fellow at the Centre for Planetary Sciences at the University of Toronto Scarborough, told CNN. Other scientists took to Twitter:

As many have pointed out, there’s not enough evidence to show that ‘Oumuamua is an alien probe—it’s just a theory that hasn’t been disproven. And as the Verge points out, Loeb may be predisposed to be on the lookout for razor-thin alien probes: He’s currently advising a project called Breakthrough Starshot, a project founded by tech entrepreneur Yuri Milner and his spouse Julia, which hopes to send a space craft similar to the proposed shape of ‘Oumuamua to Alpha Centauri, the closest star to our solar system at four light-years away. The project’s board included the late Stephen Hawking, along with Facebook’s Mark Zuckerberg. Loeb readily admits that he’s got light sails on the brain. “The fact that I’m involved in a project that uses the light sail allowed me, or encouraged me, to think about it,” he told the Verge.

Bialy, meanwhile, has a different perspective. “Most probably, our paper is wrong and there’s a more simple explanation [for ‘Oumuamua],” he says. But so far, no one’s put forward a better explanation for what the interstellar object could be. If it isn’t aliens, astrophysicists have to come up with a better option.

Finding another answer will be challenging. There’s limited data on ‘Oumuamua, since scientists could only observe it for about two weeks before it zipped beyond our solar system. It may be impossible to find the simple answer with the information we have. 

However, the fact that scientists were able to spot this interstellar object at all likely means that they could find more in the future, Bialy argues. And if scientists are better-prepared to observe interstellar objects, perhaps they can get more data on them in order figure out what they actually are. A good starting point would be to get an actual photographic image of ‘Oumuamua; right now, scientists are working with an artist’s conceptions alone, based on the measurements taken by far-away telescopes.

Until then, scientists can’t rule out the idea that  ‘Oumuamua isn’t an alien probe. Bialy hopes that will be inspiration enough to try to find out what it really is.