‘Oumuamua is not the alien probe you’re looking for

Despite what Harvard scientists say.

a cigar-shaped comet in space
An artist's idea of what 'Oumuamua might look like.European Southern Observatory/M. Kornmesser

Three things are certain in this world: death, taxes, and people going bananas over aliens. Enter famed Harvard University physicist Avi Loeb and postdoc Shmuel Bialy and their new pre-print paper, which suggests a possibility that the interstellar asteroid known as 'Oumuamua might be a lightsail-propelled spacecraft of artificial origin designed for interstellar travel. Yes, they're saying it might be aliens.

Don’t get carried away. The paper does not present any evidence of the sort—it’s basically an attempt to explain some of the object’s weird behavior with an unrealistic hypothesis. The entire riff-raff over the new paper is a good example of why extreme ideas, even from those who hail from the most prestigious institutions in the world, should be treated with caution.

Here's the deal: one year ago, 'Oumuamua came from interstellar space for a quick visit to the solar system, zipping through at 196,000 miles per hour for what was basically, in cosmic terms, a weekend trip. Once scientists realized this was the first interstellar object spotted visiting our solar system, they hastily went to work collecting as much data as they possibly could. They had barely two weeks with ground-based telescopes and about three months with the Hubble Space Telescope to observe 'Oumuamua before it was gone forever.

'Oumuamua is not your garden variety "minor planet." It's 800 meters long, 80 meters wide, composed of rock and ice mushed together into the bizarre shape of a cigar. It was pretty unclear whether the object qualified as a comet or an asteroid; its shape suggested a comet, but it was not shedding the sort of small dust comets typically shed.

And ‘Oumuamua’s lost weekend through the solar system was equally strange to boot. The object had small changes in direction and speed that could not be attributed to gravitational forces alone, accelerating as it left the solar system. A good explanation for this would be outgassing—where jets of gaseous material are expelled from the surface thanks to interactions between the sun’s heat and the object’s volatile icy components, increasing the ‘Oumuamua’s overall velocity. This also would have been a clear sign that ‘Oumuamua was a comet.

But outgassing is supposed to happen as a comet inches closer to the sun, not as it moves away. Loeb and Bialy have put forth a counterargument that suggests 'Oumuamua's movement is what we might expect if the object was designed to be propelled through space using the force of the sun's light. That's how a lightsail is supposed to work—solar radiation hits the surface and induces a force that speeds up an object as it moves through space. And something like a lightsail, optimized for interstellar travel, would have to be made by intelligent life.

In his defense of the paper, to be published next week in The Astrophysical Journal Letters, Loeb told NBC News Mach that his new hypothesis was "purely scientific and evidence-based…I follow the maxim of Sherlock Holmes: when you have excluded the impossible, whatever remains, however improbable, must be the truth."

That's a pretty wild way to come to such a radical conclusion. Michele Bannister, an astrophysicist at Queen's University Belfast in Northern Ireland, emphasizes that Loeb's hypothesis would only be appropriate if there were no other good explanations for the abrupt increase in 'Oumuamua's acceleration. "And we do have a good explanation that fits the data well," says Bannister, citing a paper published in Nature earlier this year that uses data to support the notion that outgassing occurred on the object's exit from the solar system. Bannister argues that the lack of outright outgassing observations might simply be a symptom of how little time astronomers had to study 'Oumuamua before it was too far away. "Do the data need extreme hypotheses when you have reasonable hypotheses that perfectly fit the data?" she asks rhetorically.

And if ‘Oumuamua is a comet, it’s certainly not the first to refrain from emitting small dust. 2P/Encke is a prime example of such a comet, yielding larger particles on the scale of several millimeters in diameter versus smaller bits of dust just microns in diameter.

“There’s a range of comet behaviors,” says Bannister. There are trillions on trillions of tiny ice-and-rock worlds strewing about the universe. It’s probable, she argues, that we’d expect to see one acting a bit unusual like ‘Oumuamua.

The truth is, this latest paper isn’t even the first time scientists have speculated whether ‘Oumuamua might have an origin story tied back to intelligent aliens. And for a while now, the hype around ‘Oumuamua as the first interstellar visitor on record means every little bizarre trait will be picked up on—and possibly interpreted as evidence of something outlandish.

But there’s a big difference between that speculation from a year ago and what Loeb and Bialy and are pitching now. A year ago, people were trying to understand the data as quickly as possible in order to figure out whether our instruments should look for something in particular, and that’s why wilder ideas were taken more seriously. Now, “it’s been over a year since the flyby of ‘Oumuamua,” says Bannister. “We’re not in a hurry at this point. We have all the data that’s ever going to be collected on this object.” We’re now seeking to simply increase our overall understanding of the visitor, and those things will take time to crystallize. A new hypothesis like the Harvard researchers’ is more noise than signal.

So why does this paper exist? Astrophysicist Katie Mack raised a good point on Twitter that many scientists are happy to speculate on even the most extreme explanations for a phenomenon when it can't be proven 100 percent false, even if they don't really take those explanations seriously. In space, any mysterious object could theoretically be the handiwork of aliens. But just because something eludes conventional explanation doesn't mean it's the work of intelligent lifeforms from beyond our solar system.

Loeb and Shmuel may have actually sought to provoke some strong responses through their paper. Why? Loeb is heavily involved with lightsail research in development on Earth, particularly as a part of his work as the chair of the advisory committee in the Breakthrough Starshot Initiative. A cynical reading of these events could be that Loeb pitched a weird theory about 'Oumuamua to drum up some chatter about lightsails. But Loeb is a pretty big name in his field, and it would make for a strange tactic to draft and submit a paper solely for publicity. At the very least, lightsails are on his mind, and it makes sense he would take a stab at seeing whether 'Oumuamua exhibited some characteristics of one.

It’s going to take a lot more work to really figure out the deal with ‘Oumuamua, but those like Bannister have no problem being blunt about what the object is not: “it’s not aliens.”