An alien machine already visited us, Harvard astrophysicist still contends

Harvard astrophysicist Avi Loeb says he has found good evidence for alien technology in the solar system, what could be called alien garbage, and that some other scientists don't take his ideas seriously because of "groupthink."

In his new book "Extraterrestrial: The First Sign of Intelligent Life Beyond Earth" (Houghton Mifflin Harcourt), set to be published Jan. 26, Loeb describes his journey to a radical position on the strange interstellar visitor that’s been dubbed 'Oumuamua — a cigar- or disc-shaped object that whizzed through our solar system in 2017.

When 'Oumuamua flashed through the sun's neighborhood in 2017, scientists didn't get a very good look at it, as it moved through so quickly. But even with those disadvantages, observers noted several anomalies. Loeb published a paper in 2018 arguing that the data showed an object unlikely to exist in nature: a wide, super-thin disk being pushed by sunlight and moving 16 miles per second (26 kilometers per second) through interstellar space relative to the sun. The solar system, according to Loeb, was possibly being visited by an alien light sail — possibly one that had been thrown out like technological trash by an intelligent alien civilization. He has consistently defended this idea in the years since, even as the wider scientific community has settled on the view that the object was probably natural.

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In "Extraterrestrial," Loeb makes his case for the alien interpretation of ‘Oumuamua, while responding  to the bulk of the scientific community that leans toward more mundane, natural explanations. 

'Oumuamua's biggest anomalies, which Loeb says are most important to the case for its alien origin, are its shape, its shininess and the way it moved.

Without a clear image of 'Oumuamua to work with, astronomers were left to infer its shape and size from its light — both the intensity and the way it rapidly brightened and dimmed as it rotated once every seven or eight hours. The significant difference between its brightest and dimmest reflections of sunlight led early observers to conclude it's much longer than it was wide and surprisingly bright, matching no asteroid or comet ever seen in the solar system.

That led to two possibilities: an unusually shiny, narrow cigar-shaped object, or a somewhat smaller, extraordinarily shiny disc. Later research showed that a disc was somewhat more likely based on the data, though the conventional view has leaned toward a cigar shape, which is easier to explain in nature, according to both Loeb and other researchers who have looked at the problem.

The final anomaly, and the one Loeb sees as most important, was that 'Oumuamua seemed to accelerate as it moved away from the sun. A space rock moving only due to gravity shouldn't do this, though a comet might. As the sun heats the side of a comet, gas bursts from its surface. That "off-gassing" can act like burning fuel that escapes from the bottom of a rocket engine, pushing a comet to higher velocities and new directions through space.

But the very precise telescopes trained on 'Oumuamua didn't see a trail of gas leading away from the object, which would be expected in the wake of a normal comet. That, combined with the likely disc shape, point to the object being light sail pushed by the sun, according to Loeb. 

The device might not have been sent deliberately to the solar system, he wrote. Instead, it could be the garbage of a civilization that produces huge numbers of machines that end up drifting uselessly through space — the equivalent of technological trash or "e-waste" on Earth.

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"A buoy. A grid of pods for communication. Signposts that an extraterrestrial civilization could navigate by. Launch bases for probes. Other intelligent living organisms' defunct technology or discarded technological trash," he wrote. "These all are plausible explanations for the ‘Oumuamua mystery — plausible because here on Earth, humanity is already doing these things, albeit on a far more limited scale, and we would certainly consider replicating them if and when we explore out into interstellar space."

In the years since, some scientists have offered alternative explanations for 'Oumuamua's anomalies. Maybe it's a "cosmic dust bunny" made of some fluffy, ultralight material and light enough to be pushed by sunlight like a light sail. Maybe it's a comet of nearly pure hydrogen, releasing molecules that would be invisible to telescopes. Loeb has sharply criticized these explanations, as Live Science previously reported. But now he says he appreciates that they at least treat 'Oumuamua as a deep mystery.

He reserves his sharpest criticism in the book for a "scientific establishment" engaged in "groupthink," which he says is embodied by a paper published in the journal Nature in 2019 by the International Space Science Institute's (ISSI) 'Oumuamua team. The ISSI group, following months of careful study, concluded that it's possible to explain the object's properties through natural processes. For instance, they wrote, its off-gassing could have spewed unusually large dust particles that would have been counterintuitively difficult for telescopes to detect.

(Clouds of fine dust make smudges in the sky visible to telescopes in ways loose collections of bigger clumps are not. A comet known as 2P/Encke sometimes releases a similar form of difficult-to-spot dust, the researchers noted, for reasons unknown.)

They also said that 'Oumuamua's shininess wasn't as anomalous as Loeb suggested, and actually closely matched other small bodies in the solar system. In other words: a weird comet, but not so weird a comet that it's reasonable to assume an alien origin.

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Loeb told Live Science that he's been ridiculed for his stance on 'Oumuamua, pointing to an article about his book published Jan. 4 in the Boston Globe, which quoted two critics, including one who suggested Loeb's ideas risked making astrophysicists seem like "nutballs," (the story did cite one physicist who called Loeb "brilliant"). 

No one is similarly mocked, he said, for studying higher dimensions or string theory — both "esoteric" ideas never observed in the real world. 

"Instead they get prizes or honors," Loeb said, while young researchers are warned away from studying advanced alien civilizations in favor of less "taboo" fields that won't harm their careers. Astrobiology, the study of life in space, is now taken seriously as a field, he said. But money flows toward hunts for possible signs of microbial life that are unlikely to turn up definitive proof of life — for example, the expensive hunts for oxygen in exoplanet atmospheres. Even if oxygen is found, Loeb said, that won't prove life exists on alien worlds, because natural processes also produce oxygen. Meanwhile, little cash goes to the hunt for advanced civilizations, he said, even though their signatures (like industrial pollution in their atmospheres) would be more conclusive.

Originally published on Live Science.