A little more than a year ago, on Oct. 17, 2017, an interstellar object flung itself into our solar system, bypassing Earth before heading into Jupiter’s orbit earlier this year and towards Pluto.
This object, dubbed, ‘Oumuamua didn't follow the typical behavior of asteroids or comets, and its shape and speed defied physics—all of which raised one question:
What was it?
A new paper in the journal Astrophysical Journal Letters by Avi Loeb and Shmuel Bialy at the Harvard Smithsonian Center for Astrophysics suggests that ‘Oumuamua might be one of two things: a new kind of interstellar object or an object of “artificial origin.”
In other words, an alien probe.
Loeb and Bialy have gotten a lot of attention for their theory, but they were hardly the first ones to investigate ‘Oumuamua.
When the UFO was first spotted, astronomers used the Green Bank Telescope in West Virginia to determine if the oblong, cigar-shaped rock could possibly be an instrument for sending radio signals. A Russian billionaire, Yuri Milner, who founded the $100 million research project Breakthrough Listen, led that project.
In June, NASA astronomers published a paper in Nature that declared ‘Oumuamua wasn’t an alien spy ship, just a weirdly shaped comet. Co-author Davide Farnocchia from the Center for Near Earth Object Studies at NASA’s Jet Propulsion Laboratory explained the way it accelerated instead of slowing down as it traveled through our solar system was consistent with how comets behave. A NASA press release said the speeding-up was “likely caused by jets of gaseous material expelled from its surface. This same kind of outgassing affects the motion of many comets in our solar system.”
Loeb and Bialy’s new paper questions the NASA astronomers’ conclusions, concluding that ‘Oumuamua defies every characteristic of comets as we know them.
Comets are icy and small and release gases as they warm up, producing a tail that is shaped further by solar radiation and wind.
But, Loeb told The Daily Beast, “there is no evidence for a cometary tail” around the mystery object. “Moreover, comets change the period of their spin and no such change was detected for ‘Oumuamua.”
Moreover, comets tend to decelerate, and Bialy said the Nature paper couldn't really explain why ‘Oumuamua did the opposite.
“We propose that maybe there's solar radiation pressure that hits the body and accelerates it,” Bialy said, explaining that ‘Oumuamua's unique shape could make that pressure more powerful than if it hit a normal circular comet.
The object’s “sail” shape—long and narrow with a flat surface—would allow the radiation to push it through our solar system, Bialy said.
He and Loeb estimate that it was less than a millimeter thick but about 100 meters wide. That would make it “a very thin sheet that we don't know of having any natural formation in the universe,” Bialy said.
“It's just a very long rock,” he said said. “It's something we have never before seen in our solar system.”
Paul M. Sutter, an astrophysicist at Ohio State University, doesn’t think there’s anything particularly esoteric about it. “In my opinion, based on all available evidence, ‘Oumuamua is a big dumb rock,” he said.
Sutter said that Loeb and Bialy’s theory is questionable because we don’t have precise measurements for ‘Oumuamua. “Even if we had ideal observations, it’s easy to misunderstand or misinterpret the results,” he said. “This is the first time we’ve encountered such an object, and it already has a lot of strange properties, and we don’t have a good understanding of how those properties might influence our observations.”
Sutter is inclined to believe solar radiation pressure is at play in how the object moved. But he is not sure the sail theory works, arguing that just because the interstellar object defies our current understanding of physics doesn’t mean that there isn’t physics to support its odd behavior.
“Adding something like a solar sail does not advance the conversation,” he said. “It’s not a useful hypothesis because once you include alien intelligence, you’re able to explain any observation whatsoever. Aliens can explain anything, but that means there’s no scientific power, there’s nothing to test.”
That goes for the odd shape, too. Sutter noted that it’s not often rocks get flung into our solar system, and that its long shape could simply be a product of chance.
But as a sail by which extraterrestrials could reach out to us? “It would be an exceptionally strange and wasteful way to reach us,” Sutter said. “As fast as it is, it's been cruising for potentially millions of years before encountering our solar system, and there's no way you can ‘target’ your destination over such long times.”
Loeb said he welcomed Sutter’s critique. He said that he views ‘Oumuamua like shells on a beach, and that its existence was something to consider seriously, alien object or not.
“Not all shells are the same, and similarly only a fraction of the interstellar objects might be technological debris of alien civilizations,” he said. “But we should examine anything that enters the Solar System from interstellar space in order to infer the true nature of ‘Oumuamua or other objects of its mysterious population.”