Object of planetary mass

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Infrared image of the free-flying planet CFBDSIR 2149-0403 (faint blue point in the center of the image)

Planetary mass object (English planetary-mass object , PMO for short ) is a collective term for astronomical objects with a mass larger than small bodies (asteroids and comets) and smaller than brown dwarfs , with the traditional planets of the solar system in the middle. The lower limit of size is defined by the achievement of hydrostatic equilibrium and the upper limit by a mass of about 13 Jupiter masses, which an object needs minimally for the deuterium fusion . This means that "orbiting" planets of other stars or brown dwarfs (see exoplanet) and generally dwarf planets and larger moons also belong to this class. The Sub-Brown Dwarfs also belong to the objects of planetary mass.

This term is mainly used for objects that are not gravitationally bound to a more massive body.

Definition problem and other terms

The discovery of objects that cannot be assigned to a star system poses additional problems for the clear definition of the term “ planet ”. So far, no generally recognized definition and no uniform designation for these objects has established itself in research. In German-language reports, among other things, the terms free-flying or vagabonding planet (English free floating planet , rogue planet ), loner planet , orphan planet or (the or that) Planemo (from English plane tary m ass o bject) can be found.

Visibility and presumed number

Free-flying planets are comparatively difficult to find because they do not shine in visible light, do not reflect the light of a star significantly and cannot be discovered through their influence on a star. With infrared telescopes, however, due to their own heat emissions, some candidates for such objects in the galaxy could be discovered, so that it is now assumed that there are almost twice as many free-flying planets as stars in the Milky Way , i.e. around 400 for an estimated 100–300 billion stars Billions of free-flying planets.

A similar estimate was made for a galaxy 3.8 billion light-years away , which was studied very carefully as a gravitational lens between the earth and the quasar RX J1131-1231 .

Examples

Size comparison: Sun , Cha 110913-773444 and Jupiter .

The object Cha 110913-773444 is surrounded by a disk of dust and was discovered in 2005 with the Spitzer Space Telescope . It has a mass of around eight Jupiter and triggered a debate through its discovery and unclear classification as a star or planet , from which the name “Planemo” emerged.

The object PSO J318.5-22 , the discovery of which was published on October 1, 2013, has a mass of approximately six Jupiter masses according to the current state of knowledge (May 2014) and is therefore too low-mass to be a star or brown dwarf.

The object OTS 44 was described in 2004 as the smallest brown dwarf known at the time with a protoplanetary dust disk with a mass of 15 Jupiter . According to the current state of knowledge (November 2014) its mass is around 11.5 Jupiter's masses; however, the derivation from the measurement data is considerably uncertain (5–17 Jupiter masses), so that OTS 44 is likely, but not proven, actually an object of planetary mass.

The object SIMP J013656.5 + 093347 was discovered in 2006 and assigned to the spectral class T2.5. Only later (2017) was it recognized that the object was not a brown dwarf, but a PMO. It is the closest celestial body of this type ever discovered.

Further examples of objects of planetary mass are S Ori 68 and S Ori 70 in the constellation Orion .

List of candidates (selection)

The following list contains some candidates for objects of planetary mass that are not gravitationally bound to a more massive body.

object Right ascension declination Mass
in M J 		Radius
in R J 		Distance
in Lj 		Year of
discovery 		credentials
Cha 110913-773444 11 h 9 m 13.63 s 1226555.4−77 ° 34 ′ 44.6 ″ 8th 1.8 500 2005 EPE
S Ori 68 05 h 38 m 39.1 s 1977195−2 ° 28 ′ 05 ″ 5 ? 1400 2000 EPE
S Ori 70 5381005 h 38 m 10 s 1976374−2 ° 36 ′ 26 ″ 3 1.6 1400 2002 EPE, Luhman
CFBDSIR 2149-0403 21 h 49 m 47.2 s 1959691−4 ° 03 ′ 09 ″ 4 to 7? ? 130 ± 13 2012
PSO J318.5-22 21140821 h 14 m 8 s 2225136+ 22 ° 51 ′ 36 ″ about 6 1.53 80 ± 5 2013
SIMP J013656.5 + 093347 01 h 36 m 56.6 s 2093347+ 9 ° 33 ′ 47 ″ approx. 12.7 1.2 19.92 ± 0.09 2006 EPE

See also

literature

  • Franziska Konitzer: Billions of free-flying planets. Stars and Space , July 2020, pp. 22–25

Web links

Individual evidence

  1. ^ S. Soter: What is a Planet? In: The Astronomical Journal. Volume 132, p. 2513, IOP Publishing, 2006, arxiv : astro-ph / 0608359 (English)
  2. ^ Martin Ratcliffe: State of the Universe 2008: New Images, Discoveries, and Events. Praxis Publishing Ltd., New York 2008, ISBN 978-0-387-73998-4 , p. 21 .
  3. ^ Stefan Schmitt: Word creation - Planemo. Die Zeit, December 12, 2014, accessed on December 18, 2014 ( indicates the gender “der Planemo”, probably analogous to “der Planet” (without explicitly justifying this). Other sources use “das Planemo” (probably analogous to "The object" (planemo = planetary mass object = object of planetary mass)) ).
  4. ↑ T. Sumi, K. Kamiya et al. a .: Unbound or distant planetary mass population detected by gravitational microlensing. In: Nature. 473, 2011, p. 349, doi: 10.1038 / nature10092 .
  5. ^ E. Zachos: More Than a Trillion Planets Could Exist Beyond Our Galaxy. National Geographic , February 5, 2018; accessed April 13, 2018 .
  6. ↑ a b Michael C. Liu, Eugene A. Magnier, Niall R. Deacon, Katelyn N. Allers, Trent J. Dupuy, Michael C. Kotson, Kimberly M. Aller, WS Burgett, KC Chambers, PW Draper, KW Hodapp, R. Jedicke, R.-P. Kudritzki, N. Metcalfe, JS Morgan, N. Kaiser, PA Price, JL Tonry, RJ Wainscoat: The Extremely Red, Young L Dwarf PSO J318-22: A Free-Floating Planetary-Mass Analog to Directly Imaged Young Gas-Giant Planets . In: Astrophysical Journal Letters . In Press, October 1, 2013. arxiv : 1310.0457 .
  7. ^ KL Luhmann, DE Peterson, ST Megeath: Spectroscopic Confirmation of the Least Massive Known Brown Dwarf in Chamaeleon . In: The Astrophysical Journal . 617, No. 1, 2004. doi : 10.1086 / 425228 .
  8. ↑ a b M. Bonnefoy, G. Chauvin, A.-M. Lagrange, P. Rojo, F. Allard, C. Pinte, C. Dumas, D. Homeier: A library of near-infrared integral field spectra of young ML dwarfs . In: Astronomy & Astrophysics . 562, No. 127, 2014. doi : 10.1051 / 0004-6361 / 201118270 .
  9. ↑ P. Delorme, et al .: CFBDSIR2149-0403: a 4-7 Jupiter-mass free-floating planet in the young moving group AB Doradus? . In: Astronomy & Astrophysics . 2012. arxiv : 1210.0305 .