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A terrestrial planet, telluric planet, or rocky planet, is a
planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and ...

planet
that is composed primarily of
silicate In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
rocks In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proc ...
or
metal A metal (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is appro ...

metal
s. Within the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
, the terrestrial planets accepted by the IAU are the
inner planets The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...
closest to the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
, i.e.
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
,
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...

Venus
,
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, and
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...

Mars
. Among astronomers who use the
geophysical definition of a planet Under a geophysical Geophysics () is a subject of natural science concerned with the physical processes and Physical property, physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their ...
, the
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
, Io and sometimes
Europa Europa may refer to: Places *Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regard ...
may also be considered terrestrial planets, and so may be the large rocky
protoplanet A protoplanet is a large planetary embryo that originated within a protoplanetary disc and has undergone internal melting to produce a differentiated interior. Protoplanets are thought to form out of kilometer-sized planetesimal Planetesimals ...
-asteroids
Pallas
Pallas
and Vesta.Emily Lakdawalla et al.
What Is A Planet?
The Planetary Society, 21 April 2020
The terms "terrestrial planet" and "telluric planet" are derived from
Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through the power of the Roman Republic, it became ...

Latin
words for
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
(''Terra'' and ''Tellus''), as these planets are, in terms of structure, ''Earth-like''. These planets are located between the Sun and the
asteroid belt The asteroid belt is a torus-shaped region in the Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizin ...

asteroid belt
. Terrestrial planets have a solid
planetary surface OSIRIS-REx collecting a surface sample from asteroid 101955 Bennu in 2020— ''(:File:OSIRIS-REX SamCam TAGSAM Event 2020-10-20.gif, Full-sized image)'' A planetary surface is where the solid (or liquid) material of the outer crust (geology), cru ...
, making them substantially different from the larger gaseous planets, which are composed mostly of some combination of
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
,
helium Helium (from el, ἥλιος, helios Helios; Homeric Greek: ), Latinized as Helius; Hyperion and Phaethon are also the names of his father and son respectively. often given the epithets Hyperion ("the one above") and Phaethon ("the shining" ...

helium
, and
water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known li ...

water
existing in various physical states.


Structure

All terrestrial planets in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
have the same basic structure, such as a central metallic
core Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body is broadly considered to be the torso. Functional movements are highly dependent on this part of the body, and lack of core muscular dev ...
(mostly
iron Iron () is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behav ...

iron
) with a surrounding silicate
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
. The large rocky asteroid
4 Vesta Vesta (minor-planet designation A formal minor planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur (minor planet), centaur, trans-Neptunian object and dwarf planet but not comet). S ...
has a similar structure; possibly so does the smaller one
21 Lutetia ) , mp_category=Main belt The asteroid belt is a circumstellar disc, torus-shaped region in the Solar System, located roughly between the orbits of the planets Jupiter and Mars, that is occupied by a great many solid, irregularly shaped bod ...
. Another rocky asteroid
2 Pallas Pallas (minor-planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet (asteroid, centaur (minor planet), centaur, trans-Neptunian object and dwarf planet but not comet) ...

2 Pallas
is about the same size as Vesta, but is significantly less dense; it appears to have never differentiated a core and a mantle. The Earth's
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

Moon
and Jupiter's moon Io have similar structures to the terrestrial planets, but Earth's Moon has a much smaller iron core. Another Jovian moon
Europa Europa may refer to: Places *Europe Europe is a continent A continent is one of several large landmasses. Generally identified by convention (norm), convention rather than any strict criteria, up to seven regions are commonly regard ...
has a similar density but has a significant ice layer on the surface. Terrestrial planets can have surface structures such as
canyon A canyon (; archaic British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar a ...

canyon
s,
craters
craters
,
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. A mountain differs from a plateau in having a limited summit area, and is larger than a hill, typically rising at least ...

mountain
s,
volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet a ...

volcano
es, and others, depending on the presence of an
erosive
erosive
liquid and / or tectonic activity. Terrestrial planets have '' secondary atmospheres'', generated by volcanic out-gassing or from comet impact debris. This contrasts with the outer,
giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, ...
s, whose atmospheres are ''primary'';
primary atmosphereA primary atmosphere is an atmosphere An atmosphere (from the greek words ἀτμός ''(atmos)'', meaning 'vapour', and σφαῖρα ''(sphaira)'', meaning 'ball' or 'sphere') is a layer or a set of layers of gases surrounding a planet or o ...
s were captured directly from the original
solar nebula The formation and evolution of the Solar System The Solar SystemCapitalization Capitalization ( North American English) or capitalisation ( British English) is writing a word with its first letter as a capital letter (uppercase letter) ...
.


Solar System's terrestrial planets

The
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
has four terrestrial planets:
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
,
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...

Venus
,
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
and
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, being larger than only Mercury (planet), Mercury. In English, Mars carries the name of the Mars (mythology), Roman god of war and is often referred to ...

Mars
. Only one terrestrial planet, Earth, has an active
hydrosphere The hydrosphere (from Greek#REDIRECT Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is app ...
. During the formation of the Solar System, there were many terrestrial
planetesimal Planetesimals are solid objects thought to exist in protoplanetary disks and debris disks. Per the Chamberlin–Moulton planetesimal hypothesis, they are believed to form out of cosmic dust grains. Believed to have formed in the Solar System ab ...
s and proto-planets, but most merged with or were ejected by the four terrestrial planets, leaving only Pallas and Vesta to survive. Some began to accrete and differentiate, but suffered catastrophic collisions that left only a metallic or rocky core, like
16 Psyche 16 Psyche () is a large asteroid discovered by the Italian astronomer Annibale de Gasparis Annibale de Gasparis (9 November 1819, Bugnara – 21 March 1892, Naples; ) was an Italy, Italian astronomer, known for discovering asteroids and ...
or
8 Flora Flora (minor planet designation A formal minor-planet designation is, in its final form, a number–name combination given to a minor planet A minor planet is an astronomical object in direct orbit around the Sun (or more broadly, any star ...
respectively. Many S-type and M-type asteroids may be such fragments.
Dwarf planet A dwarf planet is a small planetary-mass object that is in direct orbit of the Sun – something smaller than any of the eight classical planets, but still a world in its own right. The prototypical dwarf planet is Pluto. The interest of d ...
s, such as
Ceres Ceres most commonly refers to: * Ceres (dwarf planet) Ceres (; minor-planet designation: 1 Ceres) is the smallest recognized dwarf planet, the closest dwarf planet to the Sun, and the List of notable asteroids, largest object in the main astero ...
,
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It was the first and the largest Kuiper belt object to be discovered. After Pluto wa ...

Pluto
and Eris, are found today only from the asteroid belt outwards (although Vesta was likely a dwarf planet in the past), in the regions beyond the formation snow line (where water ice was stable under direct sunlight in the early Solar System). They are similar to terrestrial planets in that they have a solid surface, but are composed of ice and rock rather than of rock and metal. The name ''Terran'' world has been suggested to define all solid worlds (bodies assuming a rounded shape), without regard to their composition: this would include bodies such as Pluto. Some
small Solar System bodies A small Solar System body (SSSB) is an object in the Solar System that is neither a planet, a dwarf planet, nor a natural satellite. The term was first IAU definition of planet, defined in 2006 by the International Astronomical Union (IAU) as foll ...
in the inner solar system such as Vesta are quite rocky, or in the case of Psyche even metallic like Mercury, while others such as Pallas are icier. Most planetary-mass moons are ice-rock (e.g. , Callisto,
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictional ...
, and
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus'', ...

Triton
) or even primarily ice (e.g. Mimas, Tethys, and
Iapetus In Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of Ancient Greek folklore. These stories concern the Cosmogony, origin and Cosmology#Metaphysical cosmology, nature of ...
). The three exceptions are Earth's moon, which has a composition much like Earth's mantle, Jupiter's Io, which is silicate and volcanic, and Jupiter's Europa, which is believed to have an active hydrosphere. Jupiter's Ganymede, though icy, does have a metallic core like the Moon, Io, Europa, and the terrestrial planets.


Density trends

The uncompressed density of a terrestrial planet is the average density its materials would have at zero
pressure Pressure (symbol: ''p'' or ''P'') is the force In physics, a force is an influence that can change the motion (physics), motion of an Physical object, object. A force can cause an object with mass to change its velocity (e.g. moving fr ...

pressure
. A greater uncompressed density indicates greater metal content. Uncompressed density differs from the true average density (also often called "bulk" density) because compression within planet cores increases their density; the average density depends on planet size, temperature distribution, and material stiffness as well as composition. The uncompressed density of terrestrial planets (and the large rocky protoplanets Vesta and Pallas) trends towards lower values as the distance from the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
increases. Earth's Moon has a density of 3.3 g·cm−3 and Jupiter's satellites Io and Europa are 3.5 and 3.0 g·cm−3; other large satellites are icier and typically have densities less than 2 g·cm−3 (e.g. Ganymede 1.94 g·cm−3, Callisto 1.83 g·cm−3, Titan 1.88 g·cm−3). The dwarf planets Ceres, Pluto and Eris have densities of 2.2, 1.9 and 2.5 g·cm−3, respectively. (At one point Ceres was sometimes distinguished as a 'terrestrial dwarf', vs Pluto as an 'ice dwarf', but the distinction is no longer tenable. It now appears that Ceres formed in the outer Solar System and is itself quite icy.) Calculations to estimate uncompressed density inherently require a model of the planet's structure. Where there have been landers or multiple orbiting spacecraft, these models are constrained by seismological data and also moment of inertia data derived from the spacecraft orbits. Where such data is not available, uncertainties are inevitably higher. It is unknown whether extrasolar terrestrial planets in general will show to follow this trend.


Extrasolar terrestrial planets

Most of the planets discovered outside the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Solar System
are
giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibrium, rounded by its own gravity, ...
s, because they are more easily detectable. But since 2005, hundreds of potentially terrestrial extrasolar planets have also been found, with several being confirmed as terrestrial. Most of these are
super-Earth A super-Earth is an extrasolar planet 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 th ...
s, i.e. planets with masses between Earth's and Neptune's; super-Earths may be
gas planet A gas giant is a giant planet The giant planets constitute a diverse type of planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilib ...
s or terrestrial, depending on their mass and other parameters. It is likely that most known super-Earths are in fact gas planets similar to Neptune, as examination of the relationship between mass and radius of exoplanets (and thus density trends) shows a transition point at about two Earth masses. This suggests that this is the point at which significant gas envelopes accumulate. In particular, Earth and Venus may already be close to the largest possible size at which a planet can generally remain rocky. Exceptions to this are very close to their stars (and thus would have had their volatile atmospheres boiled away). During the early 1990s, the first extrasolar planets were discovered orbiting the
pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star A neutron star is the collapsed core Core or cores may refer to: Science and technology * Core (anatomy) In common parlance, the core of the body ...

pulsar
PSR B1257+12 PSR B1257+12, previously designated PSR 1257+12, alternatively designated PSR J1300+1240, is a millisecond pulsar located 2,300 light-years from the Sun in the constellation of Virgo (constellation), Virgo, rotating at about 161 times per ...
, with masses of 0.02, 4.3, and 3.9 times that of Earth's, by
pulsar timing Any planet is an extremely faint light source compared to its parent star. For example, a star like the Sun is about a billion times as bright as the reflected light from any of the planets orbiting it. In addition to the intrinsic difficulty of ...
. When 51 Pegasi b, the first planet found around a star still undergoing fusion, was discovered, many astronomers assumed it to be a gigantic terrestrial, because it was assumed no gas giant could exist as close to its star (0.052 AU) as 51 Pegasi b did. It was later found to be a gas giant. In 2005, the first planets orbiting a main-sequence star and which show signs of being terrestrial planets were found:
Gliese 876 d Gliese 876 d is an exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confirmation of detection occurred in 1 ...

Gliese 876 d
and . Gliese 876 d orbits the red dwarf
Gliese 876 Gliese 876 is a red dwarf approximately 15 light-years away from Earth in the constellation of Aquarius (constellation), Aquarius. It is one of the closest known stars to the Sun confirmed to possess a planetary system with more than two p ...
, 15
light year The light-year is a unit of length used to express astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometres () or 5.88 trillion miles ().One trillion here is long and short scales, t ...
s from Earth, and has a mass seven to nine times that of Earth and an orbital period of just two Earth days. OGLE-2005-BLG-390Lb has about 5.5 times the mass of Earth, orbits a star about 21,000 light years away in the constellation Scorpius. From 2007 to 2010, three (possibly four) potential terrestrial planets were found orbiting within the
Gliese 581 planetary system Gliese 581 () is a star of spectral type M3V (a red dwarf A red dwarf is the smallest and coolest kind of star on the main sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood o ...
. The smallest,
Gliese 581e Gliese 581e or Gl 581e is an extrasolar planet orbiting within the Gliese 581 system, located approximately 20.4 light-years away from Earth in the Libra constellation. It is the third planet discovered in the system (fourth if the disputed plane ...
, is only about 1.9 Earth masses, but orbits very close to the star. Two others,
Gliese 581c Gliese 581c (Gl 581c or GJ 581c) is a exoplanet, planet 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 classif ...

Gliese 581c
and Gliese 581d, as well as a disputed planet,
Gliese 581g Gliese 667, Gliese 581g , unofficially known as Zarmina (or Zarmina's World), is an unconfirmed (and frequently disputed) exoplanet claimed to orbit within the Gliese 581 system, twenty light-years from Earth. It was discovered by the Lick–Carne ...
, are more-massive super-Earths orbiting in or close to the habitable zone of the star, so they could potentially be habitable, with Earth-like temperatures. Another possibly terrestrial planet, , was discovered in 2011; it has at least 3.6 times the mass of Earth. The radius and composition of all these planets are unknown. The first confirmed terrestrial
exoplanet An exoplanet or extrasolar planet is a outside the . The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confirmation of detection occurred in 1992. This was followed by the confirmation of a ...

exoplanet
,
Kepler-10b Kepler-10b is the first confirmed terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets ac ...

Kepler-10b
, was found in 2011 by the
Kepler Mission The Kepler space telescope was a space telescope A space telescope or space observatory is a telescope in outer space used to observe astronomical objects. Suggested by Lyman Spitzer in 1946, the first operational telescopes were the America ...
, specifically designed to discover Earth-size planets around other stars using the
transit Transit may refer to: Arts and entertainment Film * Transit (1979 film), ''Transit'' (1979 film), a 1979 Israeli film * Transit (2005 film), ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the wo ...
method. In the same year, the released a list of 1235 extrasolar planet candidates, including six that are "Earth-size" or "super-Earth-size" (i.e. they have a radius less than 2 Earth radii) and in the
habitable zone In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses m ...

habitable zone
of their star. Since then, Kepler has discovered hundreds of planets ranging from Moon-sized to super-Earths, with many more candidates in this size range (see image). In September 2020, astronomers using reported the
detection{{Unreferenced, date=March 2018 In general, detection is the action of accessing information without specific cooperation from with the sender. In the history of radio Radio is the technology of signaling and telecommunication, communicating u ...
, for the first time, of an Earth-mass
rogue planet A rogue planet (also termed an interstellar, nomad, free-floating, unbound, orphan, wandering, starless, or sunless planet) is a planetary-mass object that does not orbit a star directly. Such objects have been ejected from the planetary system ...
(named
OGLE-2016-BLG-1928 A rogue planet (also termed an interstellar, nomad, free-floating, unbound, orphan, wandering, starless, or sunless planet) is a planetary-mass object that does not orbit a star directly. Such objects have been ejected from the planetary system ...
) unbounded by any star, and free-floating in the
Milky Way galaxy The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

Milky Way galaxy
.


List of terrestrial exoplanets

The following exoplanets have a density of at least 5 g/cm3 and a mass below Neptune's and are thus very likely terrestrial:
Kepler-10b Kepler-10b is the first confirmed terrestrial planet A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate Rock (geology), rocks or metals. Within the Solar System, the terrestrial planets ac ...

Kepler-10b
,
Kepler-20b Kepler-20b is an exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confirmation of detection occurred in 199 ...
,
Kepler-36b Kepler-36b is an exoplanet orbiting the star Kepler-36. This planet has the closest conjunction to Kepler-36c every 97 days. Its density is similar to that of iron. During their closest approach, Kepler-36b and Kepler-36c are located only 0.01 ...
, Kepler-48d, Kepler 68c,
Kepler-78b Kepler-78b (formerly known as KIC 8435766 b) is an exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confir ...

Kepler-78b
, Kepler-89b, Kepler-93b, Kepler-97b, Kepler-99b, Kepler-100b, Kepler-101c, Kepler-102b, Kepler-102d, Kepler-113b, Kepler-131b, Kepler-131c, Kepler-138c, Kepler-406b, Kepler-406c, Kepler-409b.


Frequency

In 2013, astronomers reported, based on Kepler (spacecraft), Kepler space mission data, that there could be as many as 40 billion Earth- and super-Earth-sized extrasolar planets, planets orbiting in the
habitable zone In astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses m ...

habitable zone
s of Solar analog, Sun-like stars and red dwarfs within the Milky Way. 11 billion of these estimated planets may be orbiting Sun-like stars. The nearest such planet may be 12 light-years away, according to the scientists. However, this does not give estimates for the number of extrasolar terrestrial planets, because there are planets as small as Earth that have been shown to be gas planets (see Kepler-138d).


Types

Several possible classifications for terrestrial planets have been proposed: ; Silicate planet : The standard type of terrestrial planet seen in the Solar System, made primarily of silicon-based rocky mantle (geology), mantle with a metallic (iron) core. ; Carbon planet (also called "diamond planet") : A theoretical class of planets, composed of a metal core surrounded by primarily carbon-based minerals. They may be considered a type of terrestrial planet if the metal content dominates. The Solar System contains no carbon planets but does have C-type asteroid, carbonaceous asteroids, such as Ceres and 10 Hygiea. It is unknown if Ceres has a rocky or a metallic core. ; Iron planet : A theoretical type of terrestrial planet that consists almost entirely of iron and therefore has a greater density and a smaller radius than other terrestrial planets of comparable mass.
Mercury Mercury usually refers to: * Mercury (planet) Mercury is the smallest planet in the Solar System and the closest to the Sun. Its orbit around the Sun takes 87.97 Earth days, the shortest of all the Sun's planets. It is named after the Roman g ...

Mercury
in the Solar System has a metallic core equal to 60–70% of its planetary mass, and is sometimes called an iron planet, though its surface is made of silicates and is iron-poor. Iron planets are thought to form in the high-temperature regions close to a star, like Mercury, and if the protoplanetary disk is rich in iron. ; Icy planet : A type of terrestrial planet with an icy surface of volatiles. The Solar System contains no known icy planets under the dynamical definition, but does under the geophysical definition: most planetary-mass moons (such as
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictional ...
,
Triton Triton commonly refers to: * Triton (mythology), a Greek god * Triton (moon), a satellite of Neptune Triton may also refer to: Biology * Triton cockatoo, a parrot * Triton (gastropod), a group of sea snails * ''Triton'', a synonym of ''Triturus'', ...

Triton
, and Enceladus) and many dwarf planets (such as Pluto and Eris) have such a composition. Europa is sometimes considered an icy planet due to its surface ice, but its higher density indicates that its interior is mostly rocky. Such planets can have internal saltwater oceans and cryovolcanoes erupting liquid water (i.e. an internal hydrosphere, like Europa or Enceladus); they can have an atmosphere and hydrosphere made from methane or nitrogen (like Titan). A metallic core is possible, as exists on . ; Coreless planet : A theoretical type of terrestrial planet that consists of silicate rock but has no metallic core, i.e. the opposite of an iron planet. Although the Solar System contains no coreless planets, chondrite asteroids and meteorites are common in the Solar System. Ceres and Pallas have mineral compositions similar to carbonaceous chondrites, though Pallas is significantly less hydrated.Marsset, M., Brož, M., Vernazza, P. et al. The violent collisional history of aqueously evolved (2) Pallas. Nat Astron 4, 569–576 (2020). https://doi.org/10.1038/s41550-019-1007-5 Coreless planets are thought to form farther from the star where volatile oxidizing material is more common.


See also

* Chthonian planet * Earth analog * List of potentially habitable exoplanets * Planetary habitability * Venus zone * List of gravitationally rounded objects of the Solar System


References

{{DEFAULTSORT:Terrestrial Planet Types of planet Terrestrial planets,