In 2017, 1I/‘Oumuamua was identified as the first known interstellar object in the Solar System1. Although typical cometary activity tracers were not detected, ‘Oumuamua showed a notable non-gravitational acceleration.
Here we report that the acceleration of ‘Oumuamua is due to the release of entrapped molecular hydrogen that formed through energetic processing of an H2O-rich icy body...We show that this mechanism can explain many of ‘Oumuamua’s peculiar properties without fine-tuning.
But when ‘Oumuamua was discovered, it had no tail and was too small and too far from the sun to capture enough energy to eject much water, which led astronomers to speculate wildly about its composition and what was pushing it outward. Was it a hydrogen iceberg? A large, fluffy snowflake pushed by light pressure from the sun?
Perhaps, they wondered, its strange acceleration actually came from hydrogen...If so, perhaps the force produced by the hydrogen outgassing could explain ‘Oumuamua’s odd movement.
“For a comet several kilometers across, the outgassing would be from a really thin shell relative to the bulk of the object, so both compositionally and in terms of any acceleration, you wouldn’t necessarily expect that to be a detectable effect,” she said. “But because ‘Oumuamua was so small, we think that it actually produced sufficient force to power this acceleration.”
NPR:
Scientists have come up with a simple explanation for the strange movements of our solar system's first known visitor from another star.
Oddly, this interstellar object appeared to be slightly accelerating in a way that normally is associated with the outgassing of some kind of material. But astronomers couldn't detect any comet-like tail of dust or gas...Now, though, in the journal Nature, two researchers say the answer might be the release of hydrogen from trapped reserves inside water-rich ice.
"It's an interesting, creative idea," says Karen Meech, with the Institute for Astronomy at the University of Hawaii, who leads the team that initially found and observed 'Oumuamua. "It doesn't require a super-exotic mechanism." But she still thinks it's possible that 'Oumuamua is just a regular, ordinary comet that released enough water, carbon dioxide, and carbon monoxide to account for the acceleration, and astronomers just didn't detect it.
Meech also finds the elongated shape of the object far more intriguing than the odd acceleration, which could be explained by low quantities of ordinary comet ejecta. The currently accepted explanation for the shape is that 'Oumuamua like objects are kicked out during planetary formation.
Planet formation is a messy process in which worlds emerge from the embryonic disks of gas and dust that give birth to stars themselves. As debris clumps together and grows, whirling around the central star, its gravity pushes and scatters smaller clumps throughout the disk.
Multiple theories postulate that such processes are responsible for sending ‘Oumuamua our way. Researchers have proposed that the strange object may have been thrown out of its young system after a brush with a giant planet there.
NASA:
The object, named ‘Oumuamua by its discoverers, is up to one-quarter mile (400 meters) long and highly-elongated—perhaps 10 times as long as it is wide. That aspect ratio is greater than that of any asteroid or comet observed in our solar system to date. While its elongated shape is quite surprising, and unlike objects seen in our solar system, it may provide new clues into how other solar systems formed.
