Jump to content

Planetary mass object: Difference between revisions

From Wikipedia, the free encyclopedia
Browse history interactively
← Previous editNext edit →
Content deleted Content added
VisualWikitext
Qurq (talk | contribs)
368 edits
m moved Planemo to Planetary mass object over redirect: More commonly used name
Qurq (talk | contribs)
368 edits
the purpose of the term is to describe objects which do not conform to typical expectations for a planet
Line 1: Line 1:
{{Article issues|onesource =November 2008|cleanup =June 2008|expand =June 2008}}

[[Image:Spectra of the Candidate 'Planemos.jpg|thumb|Optical spectra of six planetary mass object candidates, along with those of comparison objects.]]
[[Image:Spectra of the Candidate 'Planemos.jpg|thumb|Optical spectra of six planetary mass object candidates, along with those of comparison objects.]]


A '''planemo''' is a celestial object with mass greater than that of a [[small solar system body|minor object]], yet smaller than that of a nuclear reactive [[brown dwarf]] or [[star]]. This "bizarre class of planet-sized objects has no suns at all, and instead floats untethered through space."<ref>[http://www.msnbc.msn.com/id/19588333/?pg=4#Space_10ExtraSolarPlanets_070626 Extra Solar Planets msn.com]</ref><ref>[http://www.space.com/scienceastronomy/060803_planemo_twins.html www.space.com]</ref> The term covers all bodies within this size range, although most planemos that [[orbit]] stars are more regularly referred to with the more specific term, [[planet]] (see also [[dwarf planet]]).{{Citation needed|date=June 2008}} Planemo is a [[contraction (linguistics)|contraction]] of '''''plane'''''tary '''''m'''''ass '''''o'''''bject. The term has yet to achieve common usage in the scientific community: as of October 2007, it appeared in only four papers in the [http://arxiv.org/archive/astro-ph astro-ph archive].
A '''Planetary mass object''', '''PMO''', or '''planemo''' is a celestial object with a mass that falls within the range of the definition of a [[planet]] - i.e. a mass greater than that of a [[small solar system body|minor object]], yet smaller than that of a nuclear reactive [[brown dwarf]] or [[star]]. By definition all planets are ''planetary mass objects'' but the purpose of the term is to describe objects which do not conform to typical expectations for a planet, such as [[free floating planets]] not orbiting a star, or objects which have formed through cloud-collapse rather than accretion which are sometimes called [[sub-brown drarfs]].

==Origin of the term==
The description "planemo"<ref name="BrittPlanemosMSNBC">{{cite web |url= http://www.msnbc.msn.com/id/13149429/ |title= Mini-solar systems spark scientific debate |author= Robert Roy Britt |work= [[MSNBC]] |date= 6 June 2006 |quote= The scientists involved in the new research are calling the objects "planemos," short for planetary-mass objects that were born in the manner of stars and do not orbit normal stars. }} (Image by space artist [[Jon Lomberg]].)</ref> was first proposed in 2003 to the [[International Astronomical Union]] (IAU) by [[Gibor Basri]], Professor of Astronomy at the [[University of California, Berkeley]], to help clarify the nomenclature of [[celestial bodies]]. At the time, the world of astronomy was undergoing a debate (concluded only in 2006) as to what does, and what does not, constitute a planet. Under Basri's definition a planemo would be "''an object [rounded by self-gravity] that does not achieve core [[nuclear fusion|fusion]] during its lifetime''", regardless of its orbit. It is deliberately contrasted with Basri's suggested [[definition of planet]], ("''a planemo that orbits a [[fusor (astronomy)|fusor]]''") and was thus intended as a solution to the debate.

==Within the Solar System==
Within the Solar System, the following objects are, or have been argued to be, rounded through self-gravity and would thus qualify as planemos under Basri's definition. Please see individual articles for descriptions.

{|
||||||||||||<ol start="1">
<li>'''[[Mercury (planet)|Mercury]]'''
<li>'''[[Venus]]'''
<li>'''[[Earth]]'''
*<li>[[Moon]]
<li>'''[[Mars]]'''
<li>[[10 Hygiea|Hygiea]]
<li>[[4 Vesta|Vesta]]
<li>'''[[Ceres (dwarf planet)|Ceres]]'''
<li>[[2 Pallas|Pallas]]
<li>'''[[Jupiter]]'''
*<li>[[Io (moon)|Io]]
*<li>[[Europa (moon)|Europa]]
*<li>[[Ganymede (moon)|Ganymede]]
*<li>[[Callisto (moon)|Callisto]]
|||||| |||||| |||||| |||||| |||||| ||||||<ol start="10">
<li>'''[[Saturn]]'''
*<li>[[Mimas (moon)|Mimas]]
*<li>[[Enceladus (moon)|Enceladus]]
*<li>[[Tethys (moon)|Tethys]]
*<li>[[Dione (moon)|Dione]]
*<li>[[Rhea (moon)|Rhea]]
*<li>[[Titan (moon)|Titan]]
*<li>[[Iapetus (moon)|Iapetus]]
<li>'''[[Uranus]]'''
*<li>[[Miranda (moon)|Miranda]]
*<li>[[Ariel (moon)|Ariel]]
*<li>[[Umbriel (moon)|Umbriel]]
*<li>[[Titania (moon)|Titania]]
*<li>[[Oberon (moon)|Oberon]]
|||||| |||||| |||||| |||||| |||||| |||||| |||||| |||||| ||||||<ol start="12">
<li>'''[[Neptune]]'''
*<li>[[Triton (moon)|Triton]]
<li>[[90482 Orcus|Orcus]]
<li>'''[[Pluto]]'''
<li>[[Charon (moon)|Charon]]
<li>[[28978 Ixion|Ixion]]
<li>[[20000 Varuna|Varuna]]
<li>{{mpl|(55636) 2002 TX|300}}
<li>'''{{dp|Haumea}}'''
<li>[[50000 Quaoar|Quaoar]]
<li>'''{{dp|Makemake}}'''
<li>{{mpl|(55565) 2002 AW|197}}
<li>'''[[Eris (dwarf planet)|Eris]]'''
<li>[[90377 Sedna|Sedna]]
</ol>
|}
The list appears in order of increasing average distance from the Sun, with planets and dwarf planets in bold. The numbered planemos could possibly be counted as [[planet]]s if Basri's definition was used, with the bold ones definitely counting. However many more objects in the distant Solar System could be found that would qualify under the definition, with some astronomers predicting hundreds to be discovered.

As "round" is a relative term that would need to be precisely quantified, an eventual list could vary from this. For example, Haumea ({{mp|2003 EL|61}}) is more elliptical than spherical. Basri notes 'roundness' requires "enough [[mass]] to allow their self-gravity to overcome any material forces that might produce [[asymmetric]] shapes" and that "technically roundness means conformity to the [[equipotential surface]]." The IAU's view means an object would qualify if it "has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape."


==Recent discoveries==
==Recent discoveries==

Revision as of 11:58, 10 April 2010

Optical spectra of six planetary mass object candidates, along with those of comparison objects.

A Planetary mass object, PMO, or planemo is a celestial object with a mass that falls within the range of the definition of a planet - i.e. a mass greater than that of a minor object, yet smaller than that of a nuclear reactive brown dwarf or star. By definition all planets are planetary mass objects but the purpose of the term is to describe objects which do not conform to typical expectations for a planet, such as free floating planets not orbiting a star, or objects which have formed through cloud-collapse rather than accretion which are sometimes called sub-brown drarfs.

Recent discoveries

Cha 110913-773444 was discovered by the Spitzer Space Telescope. It is 8 times more massive than Jupiter, and an estimated 2 million years old. It is encircled by a disk of dust. It is 500 light-years away from Earth.

The first Planemos discovered outside the Solar System were those orbiting PSR 1257+12, discovered in 1992 by Aleksander Wolszczan and Dale Frail;[1] as pulsar planets, they surprised many astronomers who expected to find planets only around main sequence stars.

References

  1. ^ Pulsar Planets

Terms containing and related to the modern astronomical term 'planet', that are also a term for a type of celestial object.

See also

Look up planetary mass object in Wiktionary, the free dictionary.
Retrieved from "https://en.wikipedia.org/enwiki/w/index.php?title=Planetary_mass_object&oldid=355126437"