Planetary-mass object

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,[2] or planetary body is, by geophysical definition of celestial objects, any 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 'planet', since many objects similar in geophysical terms do not conform to conventional expectations for a planet. Planetary-mass objects can be quite diverse in origin and location. They include planets, dwarf planets, planetary-mass satellites and free-floating planets, which may have been ejected from a system (rogue planets) or formed through cloud-collapse rather than accretion (sub-brown dwarfs).

  1. ^ Brown, Michael E.; Butler, Bryan (July 2023). "Masses and densities of dwarf planet satellites measured with ALMA". The Planetary Science Journal. 4 (10): 11. arXiv:2307.04848. Bibcode:2023PSJ.....4..193B. doi:10.3847/PSJ/ace52a.
  2. ^ Weintraub, David A. (2014). Is Pluto a Planet?: A Historical Journey through the Solar System. Princeton University Press. p. 226. ISBN 978-1400852970.
  3. ^ Basri, Gibor; Brown, E. M. (May 2006). "Planetesimals to Brown Dwarfs: What is a Planet?". Annual Review of Earth and Planetary Sciences. 34: 193–216. arXiv:astro-ph/0608417. Bibcode:2006AREPS..34..193B. doi:10.1146/annurev.earth.34.031405.125058. S2CID 119338327.
  4. ^ Stern, S. Alan; Levison, Harold F. (2002). Rickman, H. (ed.). "Regarding the criteria for planethood and proposed planetary classification schemes". Highlights of Astronomy. 12. San Francisco, CA: Astronomical Society of the Pacific: 208. Bibcode:2002HiA....12..205S. doi:10.1017/S1539299600013289. ISBN 978-1-58381-086-6.

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