What does exoplanet mean?
An exoplanet is a planet orbiting a star other than the Sun, placing it beyond our Solar System. The term is standard in astronomy and science journalism, where it is used for planets detected around other stars, including rocky worlds, gas giants, and planets in multiplanet systems. Astronomers generally identify exoplanets indirectly by observing their host stars: regular changes in brightness can reveal a planet passing in transit, while measurements of a star’s motion can indicate the pull of an orbiting body. The word is especially useful because it clearly separates worlds outside the Solar System from planets such as Earth and Mars. It also carries a strong sense of scientific discovery and exploration, often appearing in discussions of potentially habitable environments and future space telescopes. In general writing, “extrasolar planet” remains a clear synonym, while “exoplanet” is the more concise and familiar choice.
nounA planet that orbits a star other than the Sun and therefore lies outside the Solar System.
- A planet orbiting a star other than the Sun.
"The newly discovered exoplanet is one of the most promising targets for atmospheric study."
"Researchers used transit photometry to search for an exoplanet whose passage across its star produced regular dips in brightness."
"A newly discovered exoplanet has become a leading target in the search for signs of an atmosphere."
The regular plural is formed by adding -s; exoplanets is the standard form in both general and scientific writing.
"The exoplanets orbit their host star at different distances."
The first confirmed exoplanets orbited a pulsar—a stellar corpse—revealing that planets can exist around the shattered remains of a star.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does exoplanet come from?
Exoplanet combines the prefix exo-, from Greek exō, meaning “outside,” with planet, from Latin planēta and Greek planētēs, meaning “wanderer” and originally referring to a wandering star. The Greek root planētēs also underlies planetary, planetesimal, and planetoid. The compound entered astronomical use in the late twentieth century, becoming increasingly established as instruments began detecting planets outside the Solar System.
Related word forms
How exoplanet is actually used
The term is standard in astronomy and widely understood in science journalism. It normally refers to a body classified as a planet and orbiting a star other than the Sun; it is not a general term for every possible world beyond the Solar System.
Easily confused with exoplanet
An exoplanet lies outside our Solar System, whereas a planet may be within it, as Earth and Mars are, or outside it.