The Mystery of Alleged Alien Object 'Oumuamua Has Been Solved, Scientists Say

A new study claims to definitively point to a natural origin for 'Oumuamua, but alien-hunting Harvard astronomer Avi Loeb is not convinced.
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The first interstellar object ever discovered in our solar system, known as ‘Oumuamua, has attracted immense interest and controversy since it was spotted in October 2017. Though this weird object is long gone, having since sped back into the interstellar wilds, a raucous debate over its origin has persisted here on Earth, driven in part by speculation among some scientists that the object could have been an alien artifact instead of a natural entity.


Now, a pair of scientists have presented a robust natural explanation that accounts for ‘Oumuamua’s strangest behaviors, including its puzzling speed boost as it hurtled through the solar system. The new research suggests that the object’s many years in interstellar space left it with an abundance of molecular hydrogen, which was transformed into gas in the presence of the Sun.

This specific mechanism could finally thread the needle between the acceleration of ‘Oumuamua and the lack of hallmark signs of so-called “outgassing” events that are associated with similar speed bursts observed in solar system objects. To that end, the “mechanism can explain many of ‘Oumuamua’s peculiar properties without fine-tuning” and “provides further support that ‘Oumuamua originated as a planetesimal relic broadly similar to Solar System comets,” according to a study published on Wednesday in Nature.

“Given the information that we have, I think that this is our best hope of explaining ‘Oumuamua without having to resort to more sensational ideas, or, as we might say in the science community, ‘fine-tuned’ ideas,” said Jennfer Bergner, an assistant professor of chemistry at the University of Berkeley who led the study, in a call with Motherboard. “We're excited about this idea because it seems very generic, and a natural explanation for a process that should be happening anyways.”


“The takeaway is that it closes the book on the five-year long fierce debate about what ‘Oumuamua was,” noted Darryl Seligman, a postdoctoral researcher at Cornell University and the co-author of the study, in a separate call with Motherboard. “But it has completely opened up what these interstellar objects are going to tell us about planet formation. It's the beginning of an entirely new field.”

‘Oumuamua ignited a scientific firestorm because it exhibited weird properties and behaviors that scientists have struggled to explain for years. At first glance, its speed burst away from the sun wasn’t all that unexpected, because space rocks in our solar system often accelerate in similar ways during outgassing events. Outgassing can occur when icy materials on these objects sublimate into gas, which causes a brief burst that is somewhat akin to a rocket burn.

“It’s important to note that non-gravitational accelerations are not, by themselves, strange,” Seligman said. “Every comet has non-gravitational accelerations. We haven't measured them on all of them, but for some, we've measured them. If you sublimate ice off of the comet, it's like a rocket effect. Ice heats up, sublimates, and produces this outflowing coma and tail, and that'll push the comet away from the coma.”

“The super-weird thing was that the amount of energy [‘Oumuamua] got from the Sun was not enough to produce the acceleration from just water or CO2 outgassing,” he continued. “That's really weird because almost every comet in the solar system is mainly made of water.” Indeed, one of the aspects of the object that made it so strange was that it did not produce the coma of dust that you would normally expect from an outgassing event.  


“It was a puzzle of why you would see something that, in some regards, behaves and looks like a comet, but you don't see any of the normal suspects to explain its dynamical behavior,” Bergner said. “This led to a lot of work in the field trying to explain how you could have something outgassing that wouldn't be spectroscopically active or how you could have even an entirely different type of body that could display this type of non-gravitational acceleration.”

“This is like saying an elephant might be a zebra without stripes”

The natural explanation for ‘Oumuamua’s strange movements cuts against a theory forwarded by Harvard astronomer Avi Loeb. Loeb, who has recently completed work for the Pentagon’s UFO investigation department, believes that the object was actually an alien artifact. It might sound outlandish, but Loeb’s approach is more rigorous than your typical alien-hunter. He and his colleagues have debunked reports of UFOs above Ukraine, and recently confirmed the presence of the first interstellar object on Earth using classified government data. 

In emails to Motherboard, Loeb defended his theory and said that the new analysis does not disprove it because he thinks the observed speed-up of ‘Oumuamua would require the complete evaporation of its hydrogen. 


“This is unreasonable because it is impossible for all the hydrogen trapped deep in the object's interior to leave to the surface without releasing the oxygen atoms with them along the way,” Loeb said. “Keep in mind that Oumuamua had the size of a football field (100-200 meters) . How can all the hydrogen from a depth of tens of meters reach the surface while leaving an object of pure oxygen behind? This is implausible.”

“Finally,” he continued, “regarding my proposal of a push by the reflection of sunlight, in September 2020 Pan STARRS observed an object exhibiting such a push without a cometary tail. This object, named 2020 SO (click here for details), was a rocket booster made of stainless steel, launched by NASA in 1966.“

“These authors claim that it was a water ice comet even though we did not see the cometary tail,” Loeb added. “This is like saying an elephant might be a zebra without stripes.”

Previously, research led by Seligman proposed that ‘Oumuamua was in fact made up of extremely rare solid hydrogen—making it the first observed example of a “hydrogen iceberg”—and that this hydrogen boiled off the surface, giving the object its distinctive shape and providing the observed speed boost without a coma. 

This hypothesis interested Bergner, who realized that radiation from cosmic rays could have seeded ‘Oumuamua with a store of so-called “amorphous” ice, a more chaotic version of the typical crystalline ice seen in most comets. This unique composition could account for the specific way that the object blasted out hydrogen that it had accumulated while traveling between stars, while leaving no trace of observable dust, according to the study.


“Hydrogen is a really compelling accelerant to explain ‘Oumumua’s behavior, but how you end up with something that's like a hydrogen iceberg is a little bit difficult to explain,” Bergner said. “I study the chemistry of icy material at really low temperatures, and from that field, we know that when you irradiate these amorphous ices you tend to lose hydrogen.”

“The thought occurred to me that if you could build up enough of this hydrogen in reserve and then outgas it when the body enters the solar system, this could give you the best of both worlds,” she continued. “I approached [Seligman] about it, and we started looking into it more and the pieces just kept falling into place.” 

Next-generation telescopes like Chile’s Vera Rubin Observatory are set to discover a lot more interstellar objects, which will give us a better idea of what’s out there—and whether ‘Oumuamua is really as unique as it appears. Already, as laid out in another recent study led by Seligman, researchers have observed a number of so-called “dark comets” that demonstrate nongravitational acceleration without comas.

“If this was a generic process, then we should see this kind of hydrogen outgassing in Oort Cloud comets as they're entering the inner solar system and starting to warm up,” Bergner said. “We would love to have our eyes out for ways to detect either small non-gravitational explorations from small bodies that are otherwise inactive. or even directly detecting molecular hydrogen.” 

Though most scientists think the interstellar objects observed to date, including ‘Oumuamua, are likely not artificial objects, they can still teach us a lot about the universe we live in—and even help us assess the potential habitability of exoplanet systems. 

“You could argue that the comets and the asteroids in the solar system have told us more about the solar system's formation and evolution than the planets themselves have,” Seligman concluded. “In some sense, you could make the same argument that potentially the interstellar comments could tell us more about exoplanets than measurements of exoplanets as far away as they are, because you get to look up closer like the building blocks of exoplanets.”