Exoplanet

noun (countable)

/ˈɛksəʊˌplænɪt/

A planet that orbits a star other than our own Sun, outside the Solar System. As of mid-2026, over 5,600 confirmed exoplanets have been identified, primarily through NASA's Kepler Space Telescope and TESS (Transiting Exoplanet Survey Satellite). Detection methods include the transit method (measuring light-curve dimming as a planet passes in front of its star) and the radial velocity method (Doppler shift of the star's light). In UPSC/GS3 context, the discovery of potentially habitable exoplanets (those in the 'Goldilocks Zone' — where liquid water could exist) is examined under astrobiology, space exploration, and India's Aditya-L1 and future ISRO missions.

✍️ Usage in a UPSC answer

The discovery of exoplanets orbiting within the habitable zones of Sun-like stars — enabled by the Kepler Space Telescope's photometric precision — has fundamentally transformed the Drake Equation's parameters and lent new urgency to ISRO's long-term roadmap for deep-space astronomical missions.

Synonyms

extrasolar planetextra-solar planetalien planetplanetary body (broader)

Antonyms

Solar System planetinner planet (in Solar context)

🌱 Word Family

exoplanet (n), exoplanetary (adj), extrasolar planet (n, synonym), super-Earth (n), hot Jupiter (n, a type), transiting exoplanet (n phrase)

🔡 Root

Greek/Latin exo- = outside, external (from Greek exō); Greek planētēs = wanderer (from planan = to wander) — planets were 'wandering stars' to ancient astronomers

📜 Etymology

The prefix exo- ('outside') derives from Greek exō. Planet comes via Latin planeta from Greek planētēs ('wanderer'), as planets appeared to wander relative to fixed stars. The compound exoplanet (also extrasolar planet) gained currency in the 1990s after the first confirmed exoplanet detection around a main-sequence star (51 Pegasi b, by Mayor and Queloz, 1995 — Nobel Physics 2019).

🧠 Memory Hook

EXO + PLANET: exo- means 'outside' (as in exoskeleton = skeleton on the outside, exodus = going outside). An exoplanet is a planet 'outside' — outside our Solar System. Mayor and Queloz won the 2019 Nobel for the first confirmed one: 51 Pegasi b. Remember: Nobel 2019 + outside our Sun = exoplanet.

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