Tidal locking is a gravitational effect where a celestial body's orbital period matches its rotational period, causing the same side to always face the object it orbits.
Tidal forces from the star stretch the planet slightly, creating bulges on opposite sides. These bulges create a torque that gradually slows the planet's rotation until one side permanently faces the star.
Tidally locked exoplanets have extreme temperature differences between their day and night sides. The dayside may be scorching hot while the nightside remains freezing cold. This creates strong winds as air flows from the hot side to the cold side.
Planets in the habitable zone of red dwarf stars are likely to be tidally locked due to their close orbits. This doesn't necessarily make them uninhabitable—the boundary between day and night (the "terminator line") could maintain moderate temperatures suitable for life.
Tidal locking occurs when a body's rotation period equals its orbital period:
Trotation = Torbit
The time it takes for a body to become tidally locked depends on several factors including its distance from the primary body, its size, density, and initial rotation rate.
Tidal locking results in synchronous rotation, where the same hemisphere always faces the primary body. This creates three distinct zones on the locked body:
All seven planets in this system are likely tidally locked to their red dwarf star. Several are in the habitable zone, making them interesting targets for studying potential life on tidally locked worlds.
The closest known exoplanet to our solar system is likely tidally locked to Proxima Centauri. It orbits in the habitable zone of its red dwarf star.
A tidally locked "hot Jupiter" with extreme temperature differences between its day and night sides. Scientists have created temperature maps of its surface using infrared observations.