Oumuamua – which means scout in Hawaiian – was spotted by a telescope in Hawaii, racing so fast it could only have come from another star system, and this was a first.
This discovery has caused an uproar in the astronomical community, which has long been searching for comet-like objects entering our solar system from the far reaches of space.
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.
This interstellar visitor, about 100 meters wide, was also notable for its brilliance and wide variation in brightness, giving the impression of a spinning metallic object.
Even stranger, however, is that after orbiting the sun, Oumuamua accelerated and went off course, propelled by a mysterious force that ejected him 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, leading to a whole host of theories.
Some were unimaginable, says Jennifer Bergner, an astrochemist at the University of California, Berkeley and co-author of the study published in Nature (New window).
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 bolide approached the sun, the heat in turn released the trapped hydrogen and acted as a propellant, sending it on an unexpected course.
Trapped hydrogen is simply the most general explanation, says Darryl Seligman of Cornell University, also a co-author on the study, in a press release.
This work undoubtedly provides the first simple and realistic explanation of the peculiarities of this object, commented Marco Micheli, astronomer at the European Space Agency (ESA).
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.
Asked by AFP about studying nature, the astrophysicist says 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.
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 intelligent extraterrestrial life, it all depends on how much evidence is needed to invoke it, the scientist comments.
We’ll never know exactly what Oumuamua was: we missed our chance. But for now, I think we provide a compelling non-alien explanation, she concludes.