A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate, rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Venus, Earth and Mars. Among astronomers who use the geophysical definition of a planet, two or three planetary-mass satellites – Earth's Moon, Io, and sometimes Europa – may also be considered terrestrial planets. The large rocky asteroids Pallas and Vesta are sometimes included as well, albeit rarely. The terms "terrestrial planet" and "telluric planet" are derived from Latin words for Earth, as these planets are, in terms of structure, Earth-like. Terrestrial planets are generally studied by geologists, astronomers, and geophysicists.
In astronomy and astrobiology, the habitable zone (HZ), or more precisely the circumstellar habitable zone (CHZ), is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. The bounds of the HZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the HZ and the objects within it may be instrumental in determining the scope and distribution of planets capable of supporting Earth-like extraterrestrial life and intelligence.
Planetary habitability is the measure of a planet's or a natural satellite's potential to develop and maintain environments hospitable to life. Life may be generated directly on a planet or satellite endogenously or be transferred to it from another body, through a hypothetical process known as panspermia. Environments do not need to contain life to be considered habitable nor are accepted habitable zones (HZ) the only areas in which life might arise.
Gliese 581 is a red dwarf star of spectral type M3V at the center of the Gliese 581 planetary system, about 20.5 light years away from Earth in the Libra constellation. Its estimated mass is about a third of that of the Sun, and it is the 101st closest known star system to the Sun. Gliese 581 is one of the oldest, least active M dwarfs known. Its low stellar activity improves the likelihood of its planets retaining significant atmospheres, and lessens the sterilizing impact of stellar flares.
Gliese 667 is a triple-star system in the constellation Scorpius lying at a distance of about 7.2 parsecs from Earth. All three of the stars have masses smaller than the Sun. There is a 12th-magnitude star close to the other three, but it is not gravitationally bound to the system. To the naked eye, the system appears to be a single faint star of magnitude 5.89.
Gliese 581c is an exoplanet orbiting within the Gliese 581 system. It is the second planet discovered in the system and the third in order from the star. With a mass at least 5.5 times that of the Earth, it is classified as a super-Earth.
Gliese 581d is a doubtful, and frequently disputed, exoplanet candidate orbiting within the Gliese 581 system, approximately 20.4 light-years away in the Libra constellation. It was the third planet claimed in the system and the fourth or fifth in order from the star. Multiple subsequent studies found that the planetary signal in fact originates from stellar activity, and thus the planet does not exist, but this remains disputed.
A Super-Earth is a type of exoplanet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.
Gliese 433 is a dim red dwarf star with multiple exoplanetary companions, located in the equatorial constellation of Hydra. The system is located at a distance of 29.6 light-years from the Sun based on parallax measurements, and it is receding with a radial velocity of +18 km/s. Based on its motion through space, this is an old disk star. It is too faint to be viewed with the naked eye, having an apparent visual magnitude of 9.81 and an absolute magnitude of 10.07.
An exoplanet is a planet located outside the Solar System. The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such until 2016; no planet discovery has yet come from that evidence. What turned out to be the first detection of an exoplanet was published among a list of possible candidates in 1988, though not confirmed until 2003. The first confirmed detection came in 1992, with the discovery of terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmation of an exoplanet orbiting a main-sequence star was made in 1995, when a giant planet was found in a four-day orbit around the nearby star 51 Pegasi. Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial-velocity method. As of 1 June 2024, there are 5,742 confirmed exoplanets in 4,237 planetary systems, with 904 systems having more than one planet. This is a list of the most notable discoveries.
Gliese 581g was a candidate exoplanet postulated to orbit within the Gliese 581 system, twenty light-years from Earth. It was discovered by the Lick–Carnegie Exoplanet Survey, and was the sixth planet claimed to orbit the star; however, its existence could not be confirmed by the European Southern Observatory (ESO) / High Accuracy Radial Velocity Planet Searcher (HARPS) survey team, and was ultimately refuted. It was thought to be near the middle of the habitable zone of its star, meaning it could sustain liquid water—a necessity for all known life—on its surface, if there are favorable atmospheric conditions on the planet.
HD 85512 b is a currently-disputed exoplanet orbiting HD 85512, a K-type main-sequence star approximately 37 light-years from Earth in the constellation of Vela.
Kepler-22b is an exoplanet orbiting within the habitable zone of the Sun-like star Kepler-22. It is located about 640 light-years from Earth in the constellation of Cygnus. It was discovered by NASA's Kepler Space Telescope in December 2011 and was the first known transiting planet to orbit within the habitable zone of a Sun-like star, where liquid water could exist on the planet's surface. Kepler-22 is too dim to be seen with the naked eye.
Gliese 667 Cc is an exoplanet orbiting within the habitable zone of the red dwarf star Gliese 667 C, which is a member of the Gliese 667 triple star system, approximately 23.62 light-years away in the constellation of Scorpius. The exoplanet was found by using the radial velocity method, from radial-velocity measurements via observation of Doppler shifts in the spectrum of the planet's parent star.
The theorized habitability of red dwarf systems is determined by a large number of factors. Modern evidence indicates that planets in red dwarf systems are unlikely to be habitable, due to their low stellar flux, high probability of tidal locking and thus likely lack of magnetospheres and atmospheres, small circumstellar habitable zones and the high stellar variation experienced by planets of red dwarf stars. However, the sheer numbers and longevity of red dwarfs could provide ample opportunity to realize any small possibility of habitability.
Kepler-296e is a confirmed super-Earth exoplanet orbiting within the habitable zone of Kepler-296. The planet was discovered by NASA's Kepler spacecraft using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. NASA announced the discovery of the exoplanet on 26 February 2014.
Mikko Tuomi is a Finnish astronomer from the University of Hertfordshire, most known for his contributions to the discovery of a number of exoplanets, among them the Proxima Centauri b which orbits the closest star to the Sun. Mikko Tuomi was the first to find indications of the existence of Proxima Centauri b in archival observation data. Other exoplanets to whose discovery or study Tuomi has contributed include HD 40307, HD 154857 c, Kapteyn c, Gliese 682 c, HD 154857, Gliese 221, Gliese 581 g and the planetary system orbiting Tau Ceti. He has led the development of new data analysis techniques for distinguishing observations caused by natural activity of the star and those caused by planets orbiting them.
Kepler-737b is a super-Earth exoplanet 669 light years away. There is a chance it could be on the inner edge of the habitable zone.
