3 explanations for ‘Oumuamua that aren’t alien spaceships

HITTING THE GAS ‘Oumuamua had its foot on the accelerator as it left the solar system. Some astronomers think the object was spewing jets of gas, as shown in this artist’s illustration, although there’s no evidence of that. Others think it was pushed by radiation from the sun. NASA, ESA, STScI
Possibilities for the interstellar object include a fluffy fractal and a comet skeleton

By Lisa Grossman | ScienceNews

The first known interstellar visitor to the solar system is keeping astronomers guessing.

Ever since it was spotted in October 2017, major mysteries have dogged the object, known as ‘Oumuamua (SN Online: 10/27/17). Astronomers don’t know where it came from in the galaxy. And they’ve disagreed over whether ‘Oumuamua is an asteroid, a comet or something else entirely.

One of the strangest mysteries is how ‘Oumuamua sped up after it slung around the sun and fled the solar system, a motion that can’t be explained by the gravitational forces of the sun or other celestial bodies alone. The most natural explanation is that ‘Oumuamua spouts gas like a comet, which would have given the object an extra push away from the sun — except astronomers saw no signs of such outgassing.

In November, Harvard University astronomers Shmuel Bialy and Avi Loeb sparked a firestorm of media coverage when they suggested that the acceleration could be explained if ‘Oumuamua is an alien spaceship, in a paper published in Astrophysical Journal Letters. In particular, the duo suggested, the object could be a solar sail: a large flat sheet less than 1 millimeter thick that uses pushes from starlight to navigate the galaxy (SN: 9/10/11, p. 18). Loeb is part of an organization called the Breakthrough Initiative that has suggested sending solar sails to visit a nearby planet orbiting the star Proxima Centauri (SN Online: 8/25/16). Maybe some other spacefaring civilization sent a similar sail to visit us, Loeb argues.

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