Interstellar Object ‚Oumuamua Is Probably a Small, Surprisingly Shiny Comet

An artist’s illustration of the interstellar object ‚Oumuamua passing through the solar system in October 2017. Observations of ‚Oumuamua indicate that it must be very elongated because of its dramatic variations in brightness as it tumbled through space. Credit: M. Kornmesser/European Southern Observatory
The history-making interstellar visitor ‚Oumuamua is a relatively small and reflective object, a new study suggests.

By Mike Wall |

Astronomers spotted ‚Oumuamua streaking through the inner solar system in October 2017 and quickly determined, based on its trajectory, that it’s not from around here. No object from interstellar space had ever been confirmed in our solar system before.

Researchers therefore scrambled to learn more about ‚Oumuamua, training a variety of telescopes on the mysterious body as it barreled toward the outer solar system. No instrument was able to resolve ‚Oumuamua, but measurements of its brightness over time indicated that it’s an oddly tumbling, needle-shaped rock perhaps six times longer than it is wide. [‚Oumuamua: Our 1st Interstellar Visitor Explained in Photos]

Astronomers also noticed that ‚Oumuamua was displaying „nongravitational acceleration“ — motion not attributable to the gravitational pull of the sun or any other solar system body. Such motion could be caused by „outgassing,“ strongly suggesting that ‚Oumuamua is a comet rather than an asteroid, scientists argued in a study published this summer.

(A different research team recently put forward an alternative hypothesis to explain the acceleration — that ‚Oumuamua may be a „sailcraft“ built by an alien civilization.)

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