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But researchers think they finally have the mystery object pegged: It could be a shard of nitrogen ice broken off a Pluto–like planet orbiting another star.
Alan Jackson and Steven Desch, planetary scientists at Arizona State University in Tempe, set out to discover what other kind of evaporating ice could give ‘Oumuamua a big enough nudge to explain its movement.
The pair reported their results March 17 at the virtual Lunar and Planetary Science Conference and in two studies published online March 16 in the Journal of Geophysical Research: Planets.
By calculating the rocketlike push on ‘Oumuamua if it were made of ices such as nitrogen, hydrogen and water, “we learned that nitrogen ice would work perfectly well,” Desch says.
Because nitrogen ice covers outer solar system bodies such as Pluto and Neptune’s moon Triton, but not smaller objects like comets, ‘Oumuamua is probably a chip off a Pluto-like exoplanet, the researchers report.
To determine how realistic that scenario is, Jackson and Desch calculated how many chunks of nitrogen ice could have been knocked off Pluto-like bodies in the early solar system.
Back then, the Kuiper Belt of objects beyond Neptune was much more crowded than it is today, including thousands of Pluto-like bodies iced with nitrogen.
Under such chaotic conditions, collisions could have broken trillions of nitrogen ice fragments off Pluto-like bodies, Jackson and Desch estimate.
If other planetary systems throw out as many shards of ice, those objects could make up about 4 percent of the bodies in interstellar space.
That would make seeing an object like ‘Oumuamua mildly unusual but not exceptional, the researchers say.
But the upcoming Vera Rubin Observatory and European Space Agency’s Comet Interceptor mission could detect more interstellar objects, says Yun Zhang, a planetary scientist at Côte d’Azur Observatory in Nice, France not involved in the research.
Getting a closer look at more of these objects could narrow down which possible explanations for ‘Oumuamua are most reasonable, she says (SN: 2/27/19).