Gliese 581d

Gliese 581d is a proposed planet orbiting the red dwarf star Gliese 581. Its existence remains unconfirmed, and the signal once attributed to it may arise from stellar activity.

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Gliese 581: Gliese 581 is a red dwarf star about 20 light-years from Earth in the constellation Libra. This is the host star whose measured motion was interpreted as evidence for Gliese 581d.
Doppler spectroscopy: Doppler spectroscopy measures motion through shifts in the wavelengths of spectral lines. The proposed planet’s evidence came from Doppler shifts in Gliese 581’s spectrum.
Gliese 581g: Gliese 581g is another disputed planet candidate once proposed to orbit Gliese 581. Like Gliese 581d, its claimed detection has been challenged by analyses of stellar activity.
Circumstellar habitable zone: The circumstellar habitable zone is the range of distances where a planet could maintain liquid water on its surface. Gliese 581d was discussed as a possible world near the outer part of this zone.
Radial velocity method: The radial velocity method detects planets through periodic shifts in a star’s spectral lines caused by orbital motion. Gliese 581d was proposed from periodic variations in its star’s measured velocity.
Kepler's laws of planetary motion: Kepler’s laws describe how planets orbit, including the relationship between orbital period and distance. These orbital rules connect the proposed signal’s period to Gliese 581d’s inferred orbit.
Gliese 581c: Gliese 581c is a reported planet orbiting Gliese 581, detected through radial-velocity observations. It provides a contrasting candidate in the same system that has remained in planetary-system models.
Planetary habitability: Planetary habitability is the capacity of a world to support conditions suitable for life. Claims about Gliese 581d’s climate prompted speculation about its potential habitability.
Michel Mayor: Michel Mayor is a Swiss astronomer who co-discovered the first exoplanet orbiting a Sun-like star. Mayor’s team announced Gliese 581d in 2007 using observations of Gliese 581.
Orbital period: An orbital period is the time a body takes to complete one orbit around another. A recurring velocity signal was assigned an orbital period for Gliese 581d.