Planetary-mass object

Source: Wikipedia, the free encyclopedia.
Not to be confused with Planet.
The planetary-mass moons to scale, compared with Mercury, Venus, Earth, Mars, and Pluto (the other planetary-mass objects beyond Neptune have never been imaged up close). Borderline Proteus and Nereid (about the same size as round Mimas) have been included. Unimaged Dysnomia (intermediate in size between Tethys and Enceladus) is not shown; it is in any case probably not a solid body.[1]

A planetary-mass object (PMO), planemo,

celestial object massive enough to achieve hydrostatic equilibrium, but not enough to sustain core fusion like a star.[3][4]

The purpose of this term is to classify together a broader range of celestial objects than '

free-floating planets, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sub-brown dwarfs
).

Usage in astronomy

While the term technically includes exoplanets and other objects, it is often used for objects with an uncertain nature or objects that do not fit in one specific class. Cases in which the term is often used:

Types

Planetary-mass satellite

Main article: Planetary-mass moon
Planetary-mass satellites larger than Pluto, the largest Solar dwarf planet.

The three largest satellites

the Moon, Europa, and Triton – are larger and more massive than the largest and most massive dwarf planets, Pluto and Eris. Another dozen smaller satellites are large enough to have become round at some point in their history through their own gravity, tidal heating from their parent planets, or both. In particular, Titan has a thick atmosphere and stable bodies of liquid on its surface, like Earth (though for Titan the liquid is methane rather than water). Proponents of the geophysical definition of planets argue that location should not matter and that only geophysical attributes should be taken into account in the definition of a planet. The term satellite planet is sometimes used for planet-sized satellites.[11]

Dwarf planets

The dwarf planet Pluto
Main article: Dwarf planet

A dwarf planet is a planetary-mass object that is neither a true planet nor a natural satellite; it is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibrious shape (usually a spheroid), but has not cleared the neighborhood of other material around its orbit. Planetary scientist and New Horizons principal investigator Alan Stern, who proposed the term 'dwarf planet', has argued that location should not matter and that only geophysical attributes should be taken into account, and that dwarf planets are thus a subtype of planet. The International Astronomical Union (IAU) accepted the term (rather than the more neutral 'planetoid') but decided to classify dwarf planets as a separate category of object.[12]

Planets and exoplanets

These paragraphs are an excerpt from Planet.[edit]
A
stellar remnant, or brown dwarf, and is not one itself.[13] The Solar System has eight planets by the most restrictive definition of the term: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion
.

Former stars

See also: Disrupted planet § Stars

In close

Accretion-powered pulsars may drive mass loss. The shrinking star can then become a planetary-mass object. An example is a Jupiter-mass object orbiting the pulsar PSR J1719−1438.[14] These shrunken white dwarfs may become a helium planet or carbon planet
.

Sub-brown dwarfs

Main article: Sub-brown dwarf
Artist's impression of a super-Jupiter around the brown dwarf 2M1207.[15]

Stars form via the gravitational collapse of gas clouds, but smaller objects can also form via

2MASS J04414489+2301513
.

Binary systems of sub-brown dwarfs are theoretically possible; Oph 162225-240515 was initially thought to be a binary system of a brown dwarf of 14 Jupiter masses and a sub-brown dwarf of 7 Jupiter masses, but further observations revised the estimated masses upwards to greater than 13 Jupiter masses, making them brown dwarfs according to the IAU working definitions.[18][19][20]

Captured planets

Rogue planets in stellar clusters have similar velocities to the stars and so can be recaptured. They are typically captured into wide orbits between 100 and 105 AU. The capture efficiency decreases with increasing cluster volume, and for a given cluster size it increases with the host/primary mass. It is almost independent of the planetary mass. Single and multiple planets could be captured into arbitrary unaligned orbits, non-coplanar with each other or with the stellar host spin, or pre-existing planetary system.[21]

Rogue planets

Main article: Rogue planet
See also: Five-planet Nice model

Several

interstellar space.[22]
Such objects are typically called rogue planets.

See also

References

  1. doi:10.3847/PSJ/ace52a
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  2. ISBN 978-1400852970
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  3. S2CID 119338327
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  4. ISBN 978-1-58381-086-6
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  5. ISSN 0004-637X
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  6. ISSN 0004-637X
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  7. ISSN 0004-6256
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  8. ISSN 0004-637X
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  9. ISSN 0004-637X
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  10. ISSN 0004-637X
    .
  11. ^ Villard, Ray (2010-05-14). "Should Large Moons Be Called 'Satellite Planets'?". Discovery News. Archived from the original on 2010-05-16. Retrieved 2011-11-04.
  12. ^ "Resolution B5 Definition of a Planet in the Solar System" (PDF). IAU 2006 General Assembly. International Astronomical Union. Retrieved January 26, 2008.
  13. S2CID 247065421. Archived
    from the original on 13 May 2022. Retrieved 13 May 2022.
  14. S2CID 206535504
    .
  15. ^ "Artist's View of a Super-Jupiter around a Brown Dwarf (2M1207)". ESA/Hubble. 19 February 2016. Archived from the original on Apr 17, 2021. Retrieved 22 February 2016.
  16. S2CID 11685964
    .
  17. S2CID 118456052
    .
  18. S2CID 15170262
    .
  19. S2CID 11153196
    .
  20. ^ Britt, Robert Roy (2004-09-10). "Likely First Photo of Planet Beyond the Solar System". Space. Archived from the original on Jan 27, 2011. Retrieved 2008-08-23.
  21. ^ On the origin of planets at very wide orbits from the re-capture of free floating planets Archived 2022-04-12 at the Wayback Machine, Hagai B. Perets, M. B. N. Kouwenhoven, 2012
  22. hdl:2060/19870013947
    .
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