A lava planet is a type of

terrestrial planet 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, ...

, with a surface mostly or entirely covered by molten

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

. Situations where such planets could exist include a young terrestrial planet just after its formation, a planet that has recently suffered a large collision event, or a planet orbiting very close to its star, causing intense irradiation and

tidal force The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...

Factors and characteristics

Lava planets would probably orbit extremely close to their parent star. In planets with eccentric orbits, the gravity from the nearby star would distort the planet periodically, with the resulting friction producing

internal heat {{Unreferenced, date=February 2012 Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, r ...

. This

tidal heating Tidal heating (also known as tidal working or tidal flexing) occurs through the tidal friction processes: orbital and rotational energy is dissipated as heat in either (or both) the surface ocean or interior of a planet or satellite. When an objec ...

could melt rocks into

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

, which would then erupt through

volcano A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Ear ...

es. This would be similar to the Solar System moon Io, orbiting close to its parent

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousandth t ...

. Io is the most geologically active world in the Solar System, with hundreds of volcanic centres and extensive lava flows. Lava worlds orbiting extremely closely to the parent star may possibly have even more volcanic activity than Io, leading some astronomers to use the term ''super-Io''. These "super-Io" exoplanets may resemble Io with extensive sulfur concentrated on their surfaces that is associated with the continuous active volcanism. However, tidal heating is not the only factor shaping a lava planet. In addition to tidal heating from orbiting close to their parent star, the intense stellar irradiation could melt the surface crust directly into lava. The entire star-facing surface of a tidally locked planet could be left covered in a lava ocean while the nightside may have lava lakes, or even lava rain caused by the condensation of vaporized rock from the dayside. The mass of the planet would also be a factor. The appearance of

plate tectonics Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

on terrestrial planets is related to planetary mass, with more massive planets than Earth expected to exhibit plate tectonics and thus more intense volcanic activity. Also, a Mega Earth may retain so much internal heat from its formation that a solid crust cannot form.

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 planetesimals that gravitation ...

s tend to have intense volcanic activity resulting from large amounts of

internal heating {{Unreferenced, date=February 2012 Internal heat is the heat source from the interior of celestial objects, such as stars, brown dwarfs, planets, moons, dwarf planets, and (in the early history of the Solar System) even asteroids such as Vesta, r ...

just after formation, even relatively small planets that orbit far from their parent stars. Lava planets can also result from giant impacts; Earth was briefly a lava planet after being impacted by a Mars-sized body which formed the Moon. A 2020 preprint study finds that lava planets have low

geometric albedo In astronomy, the geometric albedo of a celestial body is the ratio of its actual brightness as seen from the light source (i.e. at zero phase angle) to that of an ''idealized'' flat, fully reflecting, diffusively scattering ( Lambertian) disk wi ...

s of around 0.1 and that molten lava on the surface can cool and harden to form quenched glass.

Candidates

There are no known lava worlds in the

Solar System The Solar System Capitalization 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 "Solar ...

and the existence of extrasolar lava planets remains unknown. Several known exoplanets are likely lava worlds, given their small enough masses, sizes, and orbits. Likely lava exoplanets include COROT-7b, Kepler-10b, and Kepler-78b.

Factors and characteristics

Candidates

See also

References

Further reading