Direct imaging of exoplanets

Direct imaging detects exoplanets by separating their light from the much brighter light of their host stars, producing images in which the planets appear as distinct sources.

Coronagraph: An optical instrument that blocks light from a bright source while preserving nearby, fainter light. Coronagraphs suppress host-star light so nearby planets can appear in an image.
HR 8799: A young star system hosting four directly imaged giant exoplanets. Its multiple visible planets became a landmark demonstration of direct imaging.
Radial velocity method: An exoplanet detection method that measures a star’s motion through shifts in its spectrum. Unlike imaging, it detects a planet through its gravitational effect on the host star.
Exoplanet: A planet that orbits a star other than the Sun, or a stellar remnant. Direct imaging is one method for detecting and studying this broader class of worlds.
Habitable exoplanet: An exoplanet whose conditions may permit liquid water or other forms of life-supporting environments. Imaging temperate, potentially habitable planets requires far stronger starlight suppression than imaging young giants.
Adaptive optics: A technique that corrects atmospheric image distortion by rapidly adjusting a telescope’s optics. On ground-based telescopes, adaptive optics sharpens images and reduces starlight spread around planets.
Beta Pictoris b: A directly imaged gas giant orbiting the young star Beta Pictoris. Repeated observations traced its motion and enabled a measurement of its orbit.
Transit method: An exoplanet detection method that measures the dimming of a star as a planet crosses its disk. Transits reveal planets through blocked starlight rather than separated planetary light.
Inner working angle: The smallest angular separation from a bright source at which an instrument can reliably detect a fainter source. It sets how close to a host star an imaging system can detect a planet.
Earth-like exoplanet: An exoplanet resembling Earth in properties such as size, composition, or received stellar energy. Directly detecting an Earth-like planet beside a Sun-like star remains an extreme contrast challenge.

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