ExOS

EXOs is an informal shorthand sometimes used to refer to exoplanets—the planets that orbit stars other than the Sun. It is not a formal term in most scientific literature; standard usage remains exoplanets or exoplanetary systems. The label may appear in science communication and educational contexts as a concise way to reference discoveries beyond our Solar System.

Exoplanets are detected by several methods. The transit method observes periodic dips in a star’s brightness as a planet passes in front of it. The radial-velocity method detects small wobbles in a star’s motion caused by an orbiting planet’s gravity. Direct imaging captures light emitted or reflected by the planet itself, while gravitational microlensing relies on the bending of light by a planet’s gravity. Space missions such as Kepler, K2, and TESS, together with ground-based surveys, have confirmed thousands of exoplanets and shaped our understanding of planetary systems. Future missions like PLATO aim to further expand the census and characterization of exoplanets.

Exoplanets exhibit a wide diversity in size, composition, and orbits. They range from Earth-sized rocky worlds to gas giants larger than Jupiter, and from close-in orbits to long-period paths. A subset orbit within the circumstellar habitable zone, where temperatures could permit liquid water under suitable conditions. Advances in spectroscopy and photometry are increasingly enabling the study of exoplanet atmospheres, revealing molecular signatures such as water vapor, carbon dioxide, and clouds.

The study of exoplanets informs theories of planetary formation and evolution and underpins the ongoing search for potentially habitable worlds. For broader context, see exoplanet and exoplanetary science.