55 Cancri e

55 Cancri e is a super-Earth exoplanet orbiting the Sun-like star 55 Cancri A every 17.7 hours. Its close orbit produces extreme temperatures and makes it a leading target for studying rocky exoplanets.

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Orbital period: The time a body takes to complete one orbit around another body. 55 Cancri e completes an orbit in about 17.7 hours.
Exoplanet: A planet orbiting a star beyond the Solar System. 55 Cancri e is one of the best-studied nearby examples.
James Webb Space Telescope: A space observatory operating mainly in infrared wavelengths, launched in 2021. Its infrared observations have measured emission from the planet's dayside.
Earth: The third planet from the Sun and the only world known to support life. Its temperate surface contrasts with 55 Cancri e's intense stellar heating.
Tidal locking: A state in which a body's rotation period matches its orbital period, keeping one side facing its companion. Its close orbit makes synchronous rotation likely, though atmospheric circulation redistributes heat.
Radial velocity method: A technique that detects planets through periodic shifts in a star's spectral lines caused by gravitational motion. The planet's initial detection came from the star's motion, not a direct image.
Secondary eclipse: An event in which a planet passes behind its star, temporarily removing the planet's light from the combined signal. Comparing its infrared brightness before and during eclipse constrains dayside emission.
Neptune: The eighth planet from the Sun, an ice giant with a deep gaseous envelope. 55 Cancri e is far smaller than Neptune, despite overlapping the planet's broad mass regime.
Planetary equilibrium temperature: The temperature a planet would reach by balancing absorbed stellar energy against emitted radiation. Its proximity to 55 Cancri A drives exceptionally high dayside temperatures.
Transit method: A technique that detects a planet when it passes in front of its star and dims the observed light. Transit observations established its short period and measured its radius.