Scientists Say: Exomoon

This is a moon that orbits a planet outside of our solar system


Planets orbiting far away stars may have moons. Scientists are hunting these potential exomoons.

NASA/ESA/L. Hustak

Exomoon (noun, “EX-oh-moon”)

This is a moon that orbits a planet found outside our solar system. Planets that orbit stars other than our sun, such as Alpha Centauri, are known as exoplanets. If those exoplanets have moons that orbit them? Those are exomoons.

Scientists have not yet confirmed that exomoons exist. But they’ve got some evidence from powerful space telescopes such as Hubble and Kepler. These telescopes have spotted dips in light in front of stars. That dimming is what happens when an exoplanet passes in front of the star. But sometimes, that dip is followed by a second dimming. That could be the exoplanet’s exomoon, trailing along behind.

In a sentence

When exoplanets are too hot or cold to support life, scientists might look to their exomoons for aliens instead.

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Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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