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Short answer

An exoplanet is a planet outside our solar system, usually orbiting another star. Most are found by two methods: watching a star dim slightly when a planet crosses in front (transit), or measuring the star's wobble as the planet tugs it (radial velocity). [S1][S2]

Key points

• The first exoplanet around a Sun-like star was confirmed in 1995: 51 Pegasi b, a hot gas giant. [S2]
• Kepler data suggest there are more planets than stars in our galaxy. [S2]
• The closest known exoplanet, Proxima Centauri b, is about 4 light-years away. [S1]
• Scientists commonly use five discovery methods; transit and radial velocity are the main two. [S1]

Claims

• id: C1 claim: An exoplanet is a planet outside our solar system. source: S1 evidence: "is a planet outside of our solar system that usually orbits another star"
• id: C2 claim: Transit and radial velocity are the two main detection techniques. source: S1 evidence: "The two main techniques are the transit and radial velocity methods."
• id: C3 claim: Kepler data indicate more planets than stars in our galaxy. source: S2 evidence: "there are more planets than stars in our galaxy"
• id: C4 claim: The wobble method measures changes in a star's radial velocity. source: S2 evidence: "The wobble method measures changes in a star’s “radial velocity.”"

Sources

• [S1] In Depth. NASA. https://science.nasa.gov/exoplanets/facts/ . License: US government work, public domain. Accessed 2026-11-04.
• [S2] How We Find and Characterize. NASA. https://science.nasa.gov/exoplanets/how-we-find-and-characterize/ . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_xjvf2h98,
  author = {{iinventedlight}},
  title = {{Exoplanets: what they are and how they are found}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/exoplanets-basics/},
  note = {Permanent ID iil:note:xjvf2h98. License: CC-BY-4.0.},
}

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