...two astronomers have found what they call “a surprisingly simple explanation” for Oumuamua’s behavior: The object was a comet after all, propelled by minuscule amounts of hydrogen gas spurting from an icy core.
“We show that this mechanism can explain many of Oumuamua’s peculiar properties without fine-tuning,” write Jennifer Bergner, an astrochemist at the University of California, Berkeley, and Darryl Z. Seligman, of Cornell University, in a paper published on Wednesday in Nature. “This provides further support that Oumuamua originated as a planetesimal relic broadly similar to solar system comets.”
Over the last few years, some speculated that the object must be made of exotic materials, and the mystery even led to suggestions that 'Oumuamua could be some kind of alien probe or spaceship.
Now, though, in the journal Nature, two researchers say the answer might be the release of hydrogen from trapped reserves inside water-rich ice.
Jennifer B. Bergner & Darryl Z. Seligman; Acceleration of 1I/‘Oumuamua from radiolytically produced H2 in H2O ice, Nature, 2023