exoplanet

American  

[ek-soh-plan-it] / ˈɛk soʊˌplæn ɪt /

noun

Astronomy.

1. a planet that revolves around a star other than the sun.

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exoplanet British  

/ ˈɛksəʊˌplænɪt /

noun

1. a planet that orbits a star in a solar system other than that of Earth

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exoplanet Scientific  

/ ĕk′sō-plăn′ĭt /

1. See extrasolar planet

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Other Word Forms

• exoplanetary adjective

Etymology

Origin of exoplanet

First recorded in 1970–75; exo- + planet

Explanation

An exoplanet is a planet that revolves around a different sun than ours. Sometimes a pizza takes so long to be delivered, you think it must be coming from one of the furthest known exoplanets! In the 1970s, when space science was taking off, the word exoplanet was invented by attaching the combining form exo-, meaning "outside," to the word planet. That English form exo- comes from the Greek, also meaning "outside," and is used in this case because the planet is outside our solar system. Exoskeleton is another word that uses this combining form, and refers to the hard supporting structure found on the outside of certain animals such as insects and crabs.

Example Sentences

If confirmed, this world could become the first Earth-size exoplanet in a yearlong orbit that passes in front of a nearby, bright Sun-like star, making it an especially valuable target for follow-up research.

From Science Daily • Feb. 12, 2026

JWST's high resolution spectrograph allows scientists to examine exoplanet light without interference from molecules in Earth's atmosphere.

From Science Daily • Feb. 11, 2026

Among other discoveries, the telescope produced the first ever image of an exoplanet -- a planet outside our solar system -- in 2004.

From Barron's • Feb. 2, 2026

"Instead of finding the normal molecules we expect to see on an exoplanet -- like water, methane and carbon dioxide -- we saw molecular carbon, specifically C3 and C2," Zhang said.

From Science Daily • Jan. 1, 2026

This success attracted major support from NASA, the National Science Foundation, and private donors, and placed the observatory at the forefront of exoplanet science.

From Science Daily • Dec. 17, 2025