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Lee Billings: Hello and welcome to Cosmos. Lee Billings. Today we are talking about the interesting case of ‘Oumuamua, which became the first known interstellar visitor to our solar system when it swooped around the Earth and Sun in October 2017.
Our news reporter Megan Bartels wrote about the new research into this mysterious object and spoke with one of the researchers behind it.
Hello Megan!
Megan Bartels: Hello Lee. I’m glad I came here!
Claim: I mean, ‘Oumuamua stopped us all over five years ago, and it wasn’t hanging out. Astronomers have had little chance to study it. Long time no see. why are we still talking about it?
Bartel: Hmm, ‘Oumuamua was really weird. Astronomers weren’t sure if it was an asteroid or a comet, and it had a strange shape, long and thin as a cigar (or flat and thin as a pancake?). And it seemed to speed up the outbound journey in a way that scientists struggled to explain.
Claim: speed up?
Bartel: As it moved away from the Sun and away from our star’s gravity, its departure speed was faster than expected. Scientists call it “non-gravitational acceleration”.
Claim: non-gravitational acceleration. I took And because it’s strange?
Bartel: It’s actually not that weird. Comets do so all the time when they get close to the Sun. The sun’s rays heat the ice, turning it into a gas that erupts from the surface like a rocket.
Claim: But you can usually see its gas and dust trails.
Bartel: Yes, that’s right.
Claim: This explains why scientists continue to offer bizarre and unconventional ideas about what causes acceleration.
Maybe it was a big ball of dust held together by electrostatic forces, like an oversized version of the dust rabbit under the couch. Maybe it was a giant iceberg made of solid hydrogen. Or maybe it was a derelict alien spacecraft.
(Some people have said all these things. To be clear, these are all things we’ve never seen before, to the best of our knowledge. Not enough people to believe they exist.) Not necessarily for a reason.)
Bartel: that’s right. And since Oumuamua’s visit, scientists have been wrestling with that puzzle.
I spoke with one of them, Jennifer Bergner. She is a chemist at the University of California, Berkeley. She and her colleague Darryl Seligman, an astronomer at Cornell University in Ithaca, New York, said, “Oumuamua’s strange speedup may be due to something not so strange after all. Instead, they think it may be small, but otherwise a typical comet rich in water ice.
They recently published their findings in Nature.
Burger: I think what we wanted here was to provide some sort of scenario that could explain the behavior we saw without invoking exotic physics or chemistry.
Bartel: The idea here is that ‘Oumuamua, like the comets we see around us all the time, was made of dusty water ice. They collided and broke some of the water ice to form hydrogen molecules.
Burger: This differs from crystalline ice, which is a very compact ordered structure. It is amorphous. This means that there are these large kinds of pores or kind of gaps within the structure of water ice.
Bartel: But as ‘Oumuamua passed by our star, its ice softened in the sunlight, producing hydrogen and causing its non-gravitational acceleration. Astronomers kept wax dust.
Claim: Clean and very convenient. So how confident are scientists in this new idea?
Bartel: Well, it’s really hard to say. Some people think math doesn’t work. Some say there must have been visible signs of outgassing. And worst of all, we’ll never know for sure.
Burger: Oumuamua’s traits are frustratingly little observed. It will be difficult to prove anything with certainty about ‘Oumuamua.
Bartel: But astronomers can’t be held back.
Burger: ….. I am certainly excited to keep an eye out for future interstellar visitors.
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Claim: And so are we. Cosmos, thank you for listening so quickly. Our show is produced by Jeff DelViscio, Tulika Bose, and Kelso Harper. Our music was composed by Dominic Smith.
Bartel: Like and subscribe wherever you can get a podcast. For more science news, visit ScientificAmerican.com.
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