Objects · Milky Way scale
Exoplanet
A planet orbiting a star other than the Sun. Over 5,700 exoplanets have been confirmed as of 2026. They range from gas giants larger than Jupiter to rocky worlds smaller than Earth — and most stars in the Milky Way are thought to host at least one.
Nearest exoplanet
Proxima Centauri b — a roughly Earth-mass world orbiting the nearest star to the Sun at just 4.24 light-years, in the habitable zone, with an 11.2-day orbital period.
Source: NASA Exoplanet Archive
Exoplanets — the galactic census
Before 1992, we knew of exactly zero planets beyond our Solar System. Today, over 5,700 are confirmed and thousands more await verification. Statistical extrapolation from Kepler survey data suggests the Milky Way contains at least one planet per star on average — meaning over 100 billion planets in our galaxy alone.
The most common type — the sub-Neptune, between Earth and Neptune in size — does not exist in our own Solar System, making every discovery of this class a window into a different kind of world. The search is now moving beyond detection to characterisation: JWST is studying exoplanet atmospheres in unprecedented detail. See our recent JWST exoplanet atmosphere news article for the latest result, and our exoplanets overview guide for the full picture.
Frequently asked questions
- The first confirmed exoplanet discovery came in 1992, when Aleksander Wolszczan and Dale Frail detected planets orbiting a pulsar (PSR 1257+12) via radio timing variations — an unexpected result, since the violent supernova that formed the pulsar should have destroyed any planets. The first exoplanet around a Sun-like star, 51 Pegasi b, was discovered in 1995 by Michel Mayor and Didier Queloz using the radial velocity method — a hot Jupiter with a 4.2-day orbit. Mayor and Queloz shared the 2019 Nobel Prize in Physics for this discovery. The field then accelerated dramatically with the Kepler Space Telescope (2009), which used the transit method to discover thousands of planets. See our how we find exoplanets guide for a full explanation of detection methods.
- A hot Jupiter is a gas giant similar to Jupiter in size (roughly 0.3–13 Jupiter masses) but orbiting its star in a very tight orbit — typically less than 0.1 AU, with periods of just days. They were the first class of exoplanet discovered around Sun-like stars and were initially puzzling: gas giants were thought to form only in the cold outer Solar System. Hot Jupiters must have formed far from their star and then migrated inward through interactions with the protoplanetary disc or other planets. They are not common — about 1% of Sun-like stars host them — but they are easy to detect because their large size and short period produce strong, frequent transit signals. Studying their migration has reshaped planetary formation theory, including models for our own Solar System's history.
- The radius gap (also called the Fulton gap) is a striking feature in the distribution of exoplanet radii: there is a clear deficit of planets with radii between about 1.5 and 2.0 Earth radii. Planets cluster either below this gap (rocky super-Earths) or above it (gaseous sub-Neptunes). The leading explanation is photoevaporation: intense stellar UV and X-ray radiation can strip the hydrogen-rich atmospheres from planets in the right size range. Planets with massive enough envelopes retain them (sub-Neptunes); planets with thin envelopes lose them entirely (super-Earths). An alternative explanation is core-powered mass loss — heat from the planet's cooling rocky core drives atmospheric escape. Both processes likely operate. The gap was identified in Kepler data by Benjamin Fulton and colleagues in 2017.
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