Interstellar Object 'Oumuamua Probably Moved Strangely Due To Gas, Study Says

Scientists have come up with a simple explanation for the strange movements of our solar system's first known visitor from another star. NPR reports: Now, though, in the journal Nature, two researchers say the answer might be the release of hydrogen from trapped reserves inside water-rich ice. That was the notion of Jennifer Bergner, an astrochemist with the University of California, Berkeley, who recalls that she initially didn't spend much time thinking about 'Oumuamua when it was first discovered. "It's not that closely related to my field. So I was like, this is a really intriguing object, but sort of moved on with my life," she says. Then she happened to attend a seminar that featured Cornell University's Darryl Seligman, who described the object's weirdness and what might account for it. One possibility he'd considered was that it was composed entirely of hydrogen ice. Others have suggested it might instead be composed of nitrogen ice. Bergner wondered if it could just be a water-rich comet that got exposed to a lot of cosmic radiation. That radiation would release the hydrogen from the water. Then, if that hydrogen got trapped inside the ice, it could be released when the object approached the sun and began to warm up. Astronomers who observed 'Oumuamua weren't looking for that kind of hydrogen outgassing and, even if they had been, the amounts involved could have been undetectable from Earth. She teamed up with Seligman to start investigating what happens when water ice gets hit with radiation. They also did calculations to see if the object was large enough to store enough trapped hydrogen to account for the observed acceleration. And they looked to see how the structure of water ice would react to getting warmed, to see if small shifts could allow trapped gas to escape. It turns out, this actually could account for the observed acceleration, says Bergner, who notes that the kind of "amorphous" water ice found in space has a kind of "fluffy" structure that contains empty pockets where gas can collect. As this water ice warms up, its structure begins to rearrange, she says, and "you lose your pockets for hiding hydrogen. You can form channels or cracks within the water ice as parts of it are sort of compacting." As the pockets collapse and these cracks form, the trapped hydrogen would leak out into space, giving the object a push, she says.

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