Exoplanet Glossary

A biosignature is a sign(s) in a planet’s atmosphere (like oxygen or methane) that could indicate life. Not proof, but a big “maybe aliens!” clue scientists hunt for. 

An exoplanet is a planet orbiting a star beyond our Solar System. Over 5,700 confirmed—ranging from rocky Earth-twins to massive gas giants.

The Goldilocks zone is the “just right” distance from a star where liquid water could exist on a planet’s surface—not too hot, not too cold.

Hot Jupiters are massive gas giants orbiting extremely close to their stars—scorching hot with wild winds and sometimes molten glass rain.

A light-year is the distance light travels in one year—about 6 trillion miles (9.5 trillion km). Used to measure how far exoplanets are from Earth.

Radial velocity is a detection method: measuring a star’s tiny “wobble” from a planet’s gravity pulling it side to side.

A red dwarf is a small, cool star—most common in the galaxy. Many exoplanets orbit them, with dramatic red sunsets.

A rogue planet is a planet drifting through space without orbiting any star—free-floating and super cold.

A super earth is a rocky planet 1.5–2 times Earth’s size—bigger gravity, possibly thicker atmospheres or oceans.

Transit method is the most common detection method: spotting a planet by the tiny dip in starlight when it passes in front.

Tidal locking is when one side of a planet always faces its star (like our Moon to Earth)—eternal day on one side, eternal night on the other.

Water vapor is a key molecule scientists look for in exoplanet atmospheres—hint of possible oceans and habitability.