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Jupiter's moon Io in orbit around the gas giant. Io is casting a dark shadow on Jupiter's atmosphere. (Courtesy of Cassini / NASA)

Did Astronomers Just Find the First Moon Outside Our Solar System?

The potential moon is half the size of Earth and in orbit around a planet four times bigger than Jupiter.

smithsonian.com

As ever more advanced telescopes have shown that our Earth is similar to at least 17 billion Earth-like planets, astronomers have also been looking for something else—a moon in orbit around one of these exoplanets. An exomoon. And now they might have found one.

The potential moon, says Ian O'Neill for Discovery News, is half the size of Earth and in orbit around a planet four times bigger than Jupiter.

The candidate exomoon is around 45 million kilometers (0.13 AU) from its host exoplanet. As a comparison, Jupiter’s most distant satellite (S/2003 J 2) orbits over 30 million kilometers from the gas giant, so such an extreme orbit around a larger planet is certainly feasible.

The potential discovery was announced in a preliminary research paper, says Nature, and is definitely still up for debate: “After sifting through detailed observations of this event, astronomers proposed that the intervening object could be either a smallish star with a Neptune-sized planet orbiting it, or a largish planet with a moon orbiting it.”
If the latter possibility is confirmed, it would be the first ever detection of an exomoon. The problem is that there is no way to repeat the observation and know for sure.

“It’s kind of a shame because we’ll probably never know what the answer is,” says David Kipping, an astronomer at the Harvard‒Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who was not involved in the research.


No one is really surprised by the idea of exomoons. After all, moons are incredibly common in our solar system. Yet, finding the first known exomoon would be a big discovery, so the scientists are taking the more conservative interpretation, says Discovery News.

More from Smithsonian.com:

You Can’t Throw a Rock in the Milky Way Without Hitting an Earth-Like Planet
This Is an Actual Photo of a Planet in Another Solar System

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About Colin Schultz
Colin Schultz

Colin Schultz is a freelance science writer and editor based in Toronto, Canada. He blogs for Smart News and contributes to the American Geophysical Union. He has a B.Sc. in physical science and philosophy, and a M.A. in journalism.

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