‘Oumuamua may be a comet, not an asteroid

The object’s path through the solar system can’t be explained only by gravitational pull


ROCK RETHINK  A new study suggests that the interstellar traveler ‘Oumuamua (illustrated) is a comet, not an asteroid like scientists had proposed.

M. Kornmesser/ESO

The solar system’s first known interstellar visitor may not be what we thought.

Evidence is growing that the object known as ‘Oumuamua, which careened into the solar system from parts unknown before veering off, is a comet, not an asteroid.

Unlike asteroids, comets are icy and tend to be surrounded by a halo of gas and dust. Astronomers saw no signs of a halo around the approximately 400-meter-long ‘Oumuamua. So the interloper, discovered in October 2017, was dubbed an asteroid. But some scientists questioned that conclusion: The object has a reddish surface, suggestive of a comet with an outer crust shielding an icy heart.

Now, in a paper published online June 27 in Nature, researchers report that the path ‘Oumuamua took on its whirlwind tour of the solar system can’t be explained just by the gravitational tugs from the sun and other celestial bodies. Some other force must also have been acting on the object. That force could be a result of spewing gas propelling ‘Oumuamua, the scientists say, strengthening the case for a comet.

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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