Shortly before Halloween, the chairman of Harvard's astronomy department openly declared that an interstellar object hurtling through our Solar System might just be part of an extraterrestrial craft. And then…crickets.

The astrophysics blog Centauri Dreams broke the story to the cognoscenti three days later. It presented an informed survey of the academic paper which raised this brash possibility, bolstered with quotes and commentary from the paper's co-author (and noted department chair), Avi Loeb. It was well into November before outlets like CNN, Time, and The Washington Post picked up the story, replete with the inevitable sarcastic quotation marks and snarky headlines. The object, named 'Oumuamua, had a number of weird and seemingly contradictory properties; it could be that those properties appear the way they do because our observations weren't all that great. There are also other possibilities.

I read Loeb's paper—which by then had been speedily accepted for publication by the respected Astrophysical Journal. A few days later, Loeb and I sat down for the longest and—by Loeb's own account—the most serious and in-depth interview he's given on this subject. The embedded audio player following the colon at the end of this very sentence features an hour-ish edit of it, including all the highlights:

If you're not into spoken-word audio, we've got a transcript available as both plain text and as a PDF (which is probably a little easier to read).

“I’m not saying it’s aliens, but... ”

Avi Loeb is clearly nosing around one of the most extraordinary claims in astronomy. This of course requires extraordinary evidence—a requirement from which Loeb's fancy job title earns him no exceptions. But we should also avoid the inverted knee-jerk response, which goes something like, "Just because Harvard's astronomy chairman says it could be an alien craft doesn't mean it is one; and in fact, it means it isn't one, because irony! Oh, and smugness, too."

My interview with Loeb shouldn't settle this debate in favor of aliens for you, me, or anyone (Loeb himself needs far more evidence to come anywhere close to considering the case resolved). But the story of 'Oumuamua is inherently fascinating. Digging into it, non-astronomers can't help but learn a thing or three about how the Universe works. If you go down this path, you should bear in mind that alien technology has been considered, then ultimately dropped as explanations for many astronomical phenomena. 'Oumuamua will probably join this list definitively someday. But much is learned by chasing down leads—both by the field of astronomy and by curious outsiders who follow the process.

If you do listen to our interview (or read our probably-OK-ish transcript), you'll understand this debate on a subtler level than most of the people yammering about it. And the really cool thing? For reasons we discuss toward the end of our conversation, the big questions here might be dramatically resolved as soon as 2022, when an important new telescope goes online.

For those in a hurry, I'll now provide a synopsis of our interview, punctuated with time stamps to help you zip to the parts that most interest you.

There’s something about ‘Oumuamua

Our story begins on October 19 of last year (at timestamp 07:55 of the interview audio above, if you want to listen for more details than are contained in this brief write-up). That's when the object that would come to be named 'Oumuamua was first spotted by Hawaii's Pan-STARRS system, which tracks and detects near-Earth objects.

Astronomers soon established that 'Oumuamua was traveling too fast to be bound by our Sun, which meant it originated in a distant star system. This made it the first interstellar object definitively identified within our Solar System. Rightly intrigued, the astronomical community pointed a great deal of hardware toward the receding blip. Masses of observational data were thereby obtained before 'Oumuamua vanished from sight in January.

'Oumuamua was bizarre on multiple fronts from the get-go. An interesting one is that it travels at the "local standard of rest" (timestamp 15:36) amongst our local pack of stars. For reasons Loeb explains, this is a fascinating attribute—and an improbable (though not impossible) one for a natural object to have.

In June (timestamp 23:22), Nature released a rigorous analysis of 'Oumuamua's trajectory. Its authors determined—with 30 standard deviations of confidence—that the object was accelerating as it receded from the Sun. This was interpreted as proof that it was a comet, rather than an asteroid (the other likely candidate). Comets typically accelerate in this manner, propelled by the gases released by the heat of the Sun, which create their signature tails.

However, several observations ran counter to this. (timestamp 25:44). For instance, no tail was ever observed on 'Oumuamua. Neither was a coma (a comet's fuzzy head). There was no sign of water on it, and comets typically carry water. And 'Oumuamua's surface reflectivity lay far beyond the bounds associated with comets.

These and other quirks can each be explained or justified on their own. But for Loeb, the last straw was a September paper by Cambridge University's Roman Rafikov (timestamp 28:39). It argues that 'Oumuamua's spin rate (which was quite zippy—another oddity), remained constant throughout the span of observations, whereas outgassing should have perturbed the spin significantly.

Loeb concluded that outgassing could not have caused 'Oumuamua's acceleration. He considered alternate forces and settled on one that astronomers understand rather well: the pressure of radiation beaming out from the sun. But this is a much weaker force than outgassing. If it was responsible, 'Oumuamua would have to be far smaller than the quarter-mile-plus hunk of rock astronomers envisaged. Specifically, Loeb pegged it as being as small as 20 meters in diameter. And—here's the clincher—less than a millimeter thick.

Close encounters of some kind or another

No known natural process can produce anything remotely this thin in space. But this sounds an awful lot like a solar sail. And Loeb has spent many long hours modeling the physics of solar sails, in helping to lead Yuri Milner's Breakthrough Starshot project (timestamp 18:55). Yes, the cliché about hammer owners mistaking non-nails for nails instantly leaps to mind, and Loeb acknowledges this (30:07). But hammerers have also been known to identify nails accurately.

The most exotic possibility entertained in Loeb's paper (33:55) is that 'Oumuamua was on a targeted reconnaissance mission (not necessarily singling out Earth—but perhaps generally cruising the habitable zones of star systems). This is based on legacy calculations concerning the relative abundance of interstellar objects, and other factors.

Loeb and I then discuss the online archive where he and his co-author, postdoctoral fellow Shmuel Bialy, initially place their paper (36:58) and the uncommon rapidity with which Astrophysical Journal both accepted and published it (40:35). I then present Loeb with the jabs of some of his critics, to which he responds (44:51). This leads to a discussion of Loeb's philosophy about the roles and responsibilities of academics.

We close on the fascinating prospect that a large telescope debuting in 2022 might rapidly answer questions that elude current hardware (56:56). This gets back to the abundance of interstellar objects like 'Oumuamua. If they are as rare as earlier calculations indicated, the more powerful new gear will discover only a small handful of new ones. But if they are common enough to make Oumuamua's discovery unsurprising, the new telescope should rapidly spot thousands of them.

This argument is too involved to fully explore here (I'm a podcaster, not a journalist). So I urge you to listen to this section. It all but gives Loeb's controversial explanation a sell-by date, and that date is just a few years off.

Personally, I can't wait to follow events closely as they approach. Listen to this section, and you'll know the underlying issues as well as I do. However slim, there's at least a small chance that 2022 will bring jarringly suggestive evidence that 'Oumuamua is an artificial relic. And whatever the outcome, wouldn't it be cool to follow that story as it unfolds?

This interview is the most recent episode of my podcast After On. If you enjoy it, a full archive of my episodes can be found on my site or via your favorite podcast app by searching under the words "After On." The broader series is built around deep-dive interviews with world-class thinkers, founders, and scientists, and it tends to be tech- and science-heavy.