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Study: Interstellar Visitor Is Chunk of Distant Planet

Oumuamua is a cookie-shaped sliver of nitrogen ice, researchers say
By Newser Editors and Wire Services
Posted Mar 18, 2021 4:59 AM CDT

(Newser) – Our solar system’s first known interstellar visitor is neither a comet nor asteroid as first suspected and looks nothing like a cigar. A new study says the mystery object is likely a remnant of a Pluto-like world and is shaped like a cookie. Arizona State University astronomers say the strange 148-foot object appears to be made of frozen nitrogen, just like the surface of Pluto and Neptune's largest moon, Triton, the AP reports. The study's authors, Alan Jackson and Steven Desch, think an impact knocked a chunk off an icy nitrogen-covered planet 500 million years ago and sent the piece tumbling out of its own star system, toward ours. The reddish remnant is believed to be a sliver of its original self, its outer layers evaporated by cosmic radiation and, more recently, the sun.

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It's named Oumuamua, Hawaiian for scout, in honor of the observatory in Hawaii that discovered it in 2017. Visible only as a pinpoint of light millions of miles away at its closest approach, it was determined to have originated beyond our solar system because its speed and path suggested it wasn't orbiting the sun or anything else. But Oumuamua didn't fit into known categories—it looked like an asteroid but sped along like a comet. Unlike a comet, though, it didn't have a visible tail. It was even suggested it could be an alien artifact. Using its shininess, size, and shape—and that it was propelled by escaping substances that didn't produce a visible tail—Jackson and Desch devised computer models that helped them determine Oumuamua was most likely a chunk of nitrogen ice being gradually eroded, the way a bar of soap thins with use.

(Read more Oumuamua stories.)

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