An artist’s view of the first interstellar object discovered in the solar system, ‘Oumuamua.
ESA/Hubble, NASA, ESO, M. Kornme
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ESA/Hubble, NASA, ESO, M. Kornme
An artist’s view of the first interstellar object discovered in the solar system, ‘Oumuamua.
ESA/Hubble, NASA, ESO, M. Kornme
Scientists have come up with a simple explanation for the strange motions of the first known visitor to our solar system from another star.
In October 2017, astronomers in Hawaii discovered an object they named Oumuamua, which means “a messenger from far away who arrives first,” according to NASA. The reddish object was in the shape of a cigar or a pancake, and was more than 300 feet long. Its trajectory indicates that it came from another solar system, and traveled through the Milky Way for hundreds of millions of years before encountering our sun.
Oddly enough, this interstellar object appears to be accelerating slightly in a way usually associated with outgassing of some type of material. But astronomers couldn’t detect any comet-like tails of dust or gas.
Over the past few years, some have speculated that the object must be made of exotic materials, and this has even led to the mystery suggestions That “Oumuamua could be some kind of space probe or spaceship.
Now, though, in the magazine naturetwo researchers He says The answer may be the release of hydrogen from reserves trapped within the water-rich ice.
That was understandable Jennifer Bergneran astrophysicist at the University of California, Berkeley, who remembers that initially she didn’t spend much time thinking about Oumuamua when it was first discovered.
Oumuamua is circled in this image, which was made by combining multiple telescope images. Images of surrounding stars were smeared as telescopes tracked the moving object.
ESO / K. Meech et al.
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ESO / K. Meech et al.
Oumuamua is circled in this image, which was made by combining multiple telescope images. Images of surrounding stars were smeared as telescopes tracked the moving object.
ESO / K. Meech et al.
“It’s not closely related to my line of work. So I was like, ‘This is a really interesting thing,’ but it just kind of carried on with my life,” she says.
Then I happened to attend a seminar at Cornell University Daryl Seligman, who described the strangeness of the object and what might explain it. One possibility It is considered It consists entirely of hydrogen ice. Others have suggested it might be him instead component of nitrogen ice.
“Hearing about some of the explanations people have come up with to explain ‘Oumuamua’s strange properties kind of intrigued me,” says Bergner.
Bergner wondered if it could just be a water-rich comet that was exposed to a lot of cosmic radiation. This radiation will release hydrogen from the water. Then, if this hydrogen gets trapped inside the ice, it can be released as the body approaches the sun and starts to warm up. The astronomers who observed ‘Oumuamua weren’t looking for this kind of hydrogen gas release, and even if it was, the amounts involved may not be detectable from Earth.
I teamed up with Seligman to start investigating what happens when water ice is exposed to radiation. They also performed calculations to see if the object was large enough to store enough trapped hydrogen to account for the observed acceleration. They looked to see how the structure of water ice would react when heated, to see if small shifts could allow trapped gas to escape.
It turns out that this could actually explain the observed acceleration, says Bergner, who suggests that the type of “amorphous” water ice found in space has a kind of “thin” structure that contains empty pockets where gas can collect.
As this water ice gets warmer, its structure begins to rearrange, she says, “You lose pockets to hide the hydrogen. You can form channels or cracks inside the water ice where parts of it are kind of compressible.”
This Hubble Space Telescope shows Comet 2I/Borisov, the second known interstellar visitor. Unlike ‘Oumuamua, which looked like a rock, this one looked like a traditional comet.
NASA, ESA, De Jewett (University of California)
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NASA, ESA, De Jewett (University of California)
This Hubble Space Telescope shows Comet 2I/Borisov, the second known interstellar visitor. Unlike ‘Oumuamua, which looked like a rock, this one looked like a traditional comet.
NASA, ESA, De Jewett (University of California)
When the pockets collapse and these cracks form, she says, the trapped hydrogen will leak out into space, giving the body a boost.
“It’s a creative and interesting idea,” she says. Karen Mitch, with the University of Hawaii Institute of Astronomy, leading the team that initially discovered and observed ‘Oumuamua. “It doesn’t require some super-exotic mechanism.”
But she still thinks it’s possible that ‘Oumuamua could just be an ordinary, ordinary comet that released enough water, carbon dioxide, and carbon monoxide to account for the acceleration, and it wasn’t detected by astronomers.
“What a lot of people don’t realize is that in order to have a good gas detection spectrum you usually have to have a very bright comet,” she says. “Oumuamua was not shining.”
And although no one detected dust rising from it, she says it was probably not throwing up the kind of fine dust the machines are looking for. This is why she believes “it is not out of the bounds of reality that you can make it fit so perfectly into an ordinary comet.”
However, she is very happy that so many different people have been drawn into trying to spot this interstellar visitor, even though ‘Oumuamua is now too far away to notice anymore.
For her, the shape of this object remains the most pressing mystery. “It was very elongated,” she says.
A second interstellar object was discovered in 2019, and Meech says he thinks there’s always at least one inside Earth’s orbit, closer to the sun.
Another artist’s depiction of “Oumuamua traveling through space and outgassing a type of substance.
NASA, ESA, Joseph Olmsted (STScI), Frank Summers (STScI)
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NASA, ESA, Joseph Olmsted (STScI), Frank Summers (STScI)
Another artist’s depiction of “Oumuamua traveling through space and outgassing a type of substance.
NASA, ESA, Joseph Olmsted (STScI), Frank Summers (STScI)
“It’s just that we don’t see them,” she explains. “Either it’s small, or it’s dark, or it’s not in a position where you can aim telescopes.”
In 2024, the new Vera C. Rubin Observatory should come online and open a floodgate. “They expect maybe one interstellar object a year,” she says.
That’s a big deal, since the nearest star system to ours is more than four light years away, and with current technology, it would take thousands of years to send a probe there.
Meech notes that some researchers have already designed missions to intercept one of these interstellar travelers, which could contain clues about the formation of the star systems that shaped them.
“I think what’s important about this is getting all these creative ideas out there,” Meech says. “If we ever get an assignment to one of these things, we now have a wealth of testable ideas.”
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