In 2017, the mysterious bolide had so stunned astrophysicists that some hypothesized an alien spacecraft.
By Le Figaro with AFP
Published on 03/22/2023 at 21:08
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Artist’s impression of the first interstellar asteroid named “Oumuamua”, from the European Southern Observatory, November 20, 2017. M. KORNMESSER / AFP
The passage of a mysterious bolide through our solar system in 2017 had stunned astrophysicists, one of whom went so far as to see it as alien technology. A study published Wednesday, March 22 offers a “non-alien” explanation for the exotic visit.
“Oumuamua” (which means “scout” in Hawaiian) was spotted by a telescope in Hawaii and was hurtling so fast it could only have come from another star system, and this was the first time. The discovery has upset the astronomical community, which has long been searching for comet-like objects entering our solar system from the far reaches of space.
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A strange object
Except that Oumuamua didn’t look like the usual comets: it didn’t have that characteristic hairiness formed by its immense halo of gas and dust as it approached the Sun. The interstellar visitor, which is about a hundred meters wide, was also notable for its brilliance and a large variation in brightness, which gave the impression of a metallic object rotating on its own.
But even stranger, after orbiting the sun, ‘Oumuamua accelerated and went off course, propelled by a mysterious force that ejected it from the solar system. The scientists were stunned, and ended up with four months of incomplete and seemingly conflicting data they were trying to figure out. A whole series of theories arose from this. Some “were beyond imagination,” Jennifer Bergner, an astrochemist at the University of California, Berkeley, who co-authored the study published in Nature, told AFP.
Trapped hydrogen is simply the most general explanation.
Darryl Seligman, researcher at Cornell University and co-author of the study
According to his explanation, regardless of its origin, Oumuamua is a water-rich, comet-like object. During its journey through interstellar space, it was exposed to cosmic rays that bombarded the water and released hydrogen, which became trapped in the object’s body.
As the fireball neared the sun, the heat in turn released the trapped hydrogen and acted as an “engine” that sent it on an unexpected course. “Trapped hydrogen is simply the most general explanation,” explains Darryl Seligman of Cornell University and co-author of the study in a press release. This work “provides without a doubt the first simple and realistic explanation of the peculiarities of this object,” commented Marco Micheli, astronomer at the European Space Agency (ESA).
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An alien ship
But not everyone agrees with these conclusions. Starting with Avi Loeb, former director of Harvard University’s astronomy department: the eminent scientist had argued that the most believable scenario is that ‘Oumuamua is an extraterrestrial ship. A controversial thesis he defended in a 2021 book entitled The first sign of extraterrestrial intelligent life.
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Asked by AFP about studying nature, the astrophysicist confirms that saying a comet has no tail “is like saying an elephant is a zebra with no stripes”. He recalls that Comet 2I/Borisov, the second visitor from outside the solar system discovered in 2019, had a long dusty hair. Answer from Jennifer Bergner: If Oumuamua doesn’t have a tail, it’s probably because it’s much smaller than any comet observed so far, including 2I/Borisov.
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Observations in 2025
The situation could change soon. Observations from the Vera C. Rubin Telescope in Chile, scheduled to begin in 2025, are expected to discover many new comets both inside and outside the solar system. If the smaller signs show them releasing trapped hydrogen and lacking a tail, like Oumuamua, that would confirm the theory, the astrochemist added.
As for the possibility of extraterrestrial intelligent life, “it all depends on the level of evidence that is required” to invoke it, the scientist comments. “We will never know exactly what Oumuamua was, we missed our chance. But for now, I think we have a compelling non-alien explanation,” she concludes.