Photos of ‘Oumuamua went viral around the world in 2017. The cigar-shaped UFO floating in space was the first known visitor from outside our solar system. But what was it?
‘Oumuamua did not have a tail of dust or a hazy cloud of gas around it like other comets. Plus, there was that odd shape halfway between a cigar and a pie. The thing was also too small to be guilty. But the craziest thing was that ‘Oumuamua was moving faster and faster as it hurtled away from the sun. It even made some scientists dare to talk about an alien spacecraft.
Unfortunately, the reality is much less exciting. The mysterious deviation from their orbit around the sun can be explained by a simple mechanism common in icy comets: When they get warmed by the sun, they release hydrogen gas.
But if it was so natural, why didn’t the researchers think about it right away? What made Oumuamua (Hawaii Boy Scouts) so different was its size. The comet was so small that the push of the hydrogen fart was enough to slightly change its orbit around the Sun.
In fact, most comets are sloppy snowballs, which periodically approach the Sun from the far reaches of our solar system. As it heats up in sunlight, it releases water and other molecules, creating a bright halo around the comet and often a tail of gas and dust. The gases that are released are a kind of thrust that gives the comet a boost, so that the trajectory deviates slightly from the normal elliptical orbit, in which planets and asteroids travel, for example.
When ‘Oumuamua was discovered, the comet had neither a halo nor a tail. It also seemed too small and too far from the sun to emit much water. This caused a lot of confusion among astronomers. They wondered what made the object and what made it move so fast. Was it all a big hydrogen iceberg? Or just a big, airy snowflake pushed by sunlight? Or a light sail made by an extraterrestrial civilization? Or just a spacecraft with its own fuel?
Cooked with radiation
Researcher Jennifer Bergner University of California, Berkeley Thought there was one Much simpler explanation It had to be. she asked her colleague Darrell Seligman Cornell University To test the hypothesis together. “A comet hurtling through the middle of our solar system is already being cooked by cosmic rays, creating hydrogen. Our thinking was: If this happens, could it still be trapped in the object so that it can expel the hydrogen as it enters our solar system and heats up?” Bergner says. “Could this produce enough force to account for the acceleration?”
And the answer is yes. Surprisingly, Bergner found experimental research from the 1970s, 1980s, and 1990s actually showed that ice under the influence of cosmic rays can produce so much hydrogen that it remains trapped in the ice. Cosmic rays were found to be able to penetrate tens of meters deep into the ice, converting at least a quarter of the water into hydrogen gas.
“With a comet several kilometers thick, it is just a very thin shell compared to the bulk of the body. Then the release of hydrogen gas would be barely noticeable, ”says the researcher. “But because ‘Oumuamua was so small, we think the hydrogen provided enough force to cause acceleration.”
The comet, which was slightly reddish, is estimated to be 115 by 11 by 19 metres, although this is not entirely certain as it was too small and too far to be seen by telescopes. Thus, its size was determined based on the comet’s brightness. Anyway, it’s a small thing. Comets known so far have a diameter of at least one kilometer to hundreds of kilometres.
Exactly how it should be
“The great thing about Jenny’s idea is that it’s exactly what should happen to interstellar comets,” Seligman says. “We had all these stupid ideas, like hydrogen icebergs and other crazy things, and then it turned out to be the most plausible explanation.”
Her idea also explains the lack of a dust aura, something that had never been seen before. “Even if there was dust in the ice, there was no need to release it. The ice did not evaporate, but the water molecules rearranged, after which hydrogen gas was released. So that the dust did not come out, ”Seligman explains. “The main conclusion is that ‘Oumuamua is an ordinary offender who has just gone through a difficult process,” he concludes.
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