Editing Exoplanet (section)

=== Alternatives ===
The IAU's working definition is not always used. One alternate suggestion is that planets should be distinguished from [[brown dwarf]]s on the basis of their formation. It is widely thought that giant planets form through core [[Accretion (astrophysics)|accretion]], which may sometimes produce planets with masses above the deuterium fusion threshold;<ref>{{cite journal |arxiv=0710.5667 |title=Giant Planet Formation by Core Accretion |journal=Extreme Solar Systems |volume=398 |page=235 |bibcode=2008ASPC..398..235M |last1=Mordasini| first1=C. |last2=Alibert |first2=Yann |last3=Benz |first3=Willy |last4=Naef |first4=Dominique |year=2008 }}</ref><ref>{{Cite journal |arxiv=0802.1810 |title=Structure and evolution of super-Earth to super-Jupiter exoplanets. I. Heavy element enrichment in the interior |last1=Baraffe |first1=I. |date=2008 |journal=Astronomy and Astrophysics |volume=482 |issue=1 |pages=315–332 |doi=10.1051/0004-6361:20079321 |bibcode=2008A&A...482..315B |last2=Chabrier |first2=G. |last3=Barman |first3=T. |s2cid=16746688 }}</ref><ref name="bodenheimer2013">{{cite journal |title=Deuterium Burning in Massive Giant Planets and Low-mass Brown Dwarfs Formed by Core-nucleated Accretion |journal=The Astrophysical Journal |date=2013 |volume=770 |issue=2 |page=120 |doi=10.1088/0004-637X/770/2/120 |arxiv=1305.0980 |bibcode=2013ApJ...770..120B |last1=Bodenheimer |first1=Peter |last2=D'Angelo |first2=Gennaro |last3=Lissauer |first3=Jack J. |last4=Fortney |first4=Jonathan J. |last5=Saumon |first5=Didier |s2cid=118553341 }}</ref> massive planets of that sort may have already been observed.<ref>{{cite journal |doi=10.1051/0004-6361/200912427 |title=The SOPHIE northern extrasolar planets. I. A companion close to the planet/brown-dwarf transition around HD16760 |last1=Bouchy |first1=François |last2=Hébrard |first2=Guillaume |last3=Udry |first3=Stéphane |last4=Delfosse |first4=Xavier |last5=Boisse |first5=Isabelle |last6=Desort |first6=Morgan |last7=Bonfils |first7=Xavier |last8=Eggenberger |first8=Anne |last9=Ehrenreich |first9=David |last10=Forveille |first10=Thierry |last11=Le Coroller |first11=Hervé |last12=Lagrange |first12=Anne-Marie |last13=Lovis |first13=Christophe |last14=Moutou |first14=Claire |last15=Pepe |first15=Francesco |last16=Perrier |first16=Christian |last17=Pont |first17=Frédéric |last18=Queloz |first18=Didier |last19=Santos |first19=Nuno C. |last20=Ségransan |first20=Damien |last21=Vidal-Madjar |first21=Alfred |date=2009 |journal=Astronomy and Astrophysics |volume=505 |issue=2 |pages=853–858 |bibcode=2009A&A...505..853B |doi-access=free }}</ref> Brown dwarfs form like stars from the direct gravitational collapse of clouds of gas, and this formation mechanism also produces objects that are below the {{Jupiter mass|13|jup=y|link=y}} limit and can be as low as {{Jupiter mass|1|jup=y}}.<ref name=ShivKumar>{{cite journal| bibcode=2003IAUS..211..529B| title=Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?| last1=Kumar| first1=Shiv S.|volume=211| date=2003| page=532| journal=Brown Dwarfs }}</ref> Objects in this mass range that orbit their stars with wide separations of hundreds or thousands of [[astronomical unit]]s (AU) and have large star/object mass ratios likely formed as brown dwarfs; their atmospheres would likely have a composition more similar to their host star than accretion-formed planets, which would contain increased abundances of heavier elements. Most directly imaged planets as of April 2014 are massive and have wide orbits so probably represent the low-mass end of a brown dwarf formation.<ref>{{Cite journal | doi = 10.1088/0004-637X/794/2/159| title = A Statistical Analysis of Seeds and Other High-Contrast Exoplanet Surveys: Massive Planets or Low-Mass Brown Dwarfs?| journal = The Astrophysical Journal| volume = 794| issue = 2| page = 159| year = 2014| last1 = Brandt | first1 = T. D. | last2 = McElwain | first2 = M. W. | last3 = Turner | first3 = E. L. | last4 = Mede | first4 = K. | last5 = Spiegel | first5 = D. S. | last6 = Kuzuhara | first6 = M. | last7 = Schlieder | first7 = J. E. | last8 = Wisniewski | first8 = J. P. | last9 = Abe | first9 = L.| last10 = Biller | first10 = B.| last11 = Brandner | first11 = W.| last12 = Carson | first12 = J.| last13 = Currie | first13 = T.| last14 = Egner | first14 = S.| last15 = Feldt | first15 = M.| last16 = Golota | first16 = T.| last17 = Goto | first17 = M.| last18 = Grady | first18 = C. A.| last19 = Guyon | first19 = O.| last20 = Hashimoto | first20 = J.| last21 = Hayano | first21 = Y.| last22 = Hayashi | first22 = M.| last23 = Hayashi | first23 = S.| last24 = Henning | first24 = T.| last25 = Hodapp | first25 = K. W.| last26 = Inutsuka | first26 = S.| last27 = Ishii | first27 = M.| last28 = Iye | first28 = M.| last29 = Janson | first29 = M.| last30 = Kandori | first30 = R.| display-authors = etal| bibcode = 2014ApJ...794..159B|arxiv = 1404.5335 | s2cid = 119304898}}</ref> One study suggests that objects above {{Jupiter mass|10|jup=y}} formed through gravitational instability and should not be thought of as planets.<ref>{{Cite journal|last=Schlaufman|first=Kevin C.|date=2018-01-22|title=Evidence of an Upper Bound on the Masses of Planets and its Implications for Giant Planet Formation|journal=The Astrophysical Journal|volume=853|issue=1|pages=37|doi=10.3847/1538-4357/aa961c|arxiv=1801.06185|bibcode=2018ApJ...853...37S|s2cid=55995400|issn=1538-4357 |doi-access=free }}</ref>

Also, the 13-Jupiter-mass cutoff does not have a precise physical significance. Deuterium fusion can occur in some objects with a mass below that cutoff.<ref name="bodenheimer2013" /> The amount of deuterium fused depends to some extent on the composition of the object.<ref>{{Cite journal | doi = 10.1088/0004-637X/727/1/57| title = The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets| journal = The Astrophysical Journal| volume = 727| issue = 1| page = 57| year = 2011| last1 = Spiegel | first1 = D. S. |last2=Burrows |first2=Adam | last3 = Milsom | first3 = J. A. | bibcode = 2011ApJ...727...57S|arxiv = 1008.5150 | s2cid = 118513110}}</ref> In 2011, the [[Extrasolar Planets Encyclopaedia]] included objects up to 25 Jupiter masses, saying, "The fact that there is no special feature around {{Jupiter mass|13|jup=y}} in the observed mass spectrum reinforces the choice to forget this mass limit".<ref>{{cite journal|last1=Schneider |first1=J. |last2=Dedieu |first2=C. |last3=Le Sidaner |first3=P. |last4=Savalle |first4=R. |last5=Zolotukhin |first5=I. |title=Defining and cataloging exoplanets: The exoplanet.eu database| date=2011| volume=532| issue=79| journal=[[Astronomy & Astrophysics]] |arxiv=1106.0586| doi=10.1051/0004-6361/201116713|pages=A79 |bibcode=2011A&A...532A..79S|s2cid=55994657 }}</ref> As of 2016, this limit was increased to 60 Jupiter masses<ref>{{cite book|last=Schneider|first=Jean|title=Exoplanets versus brown dwarfs: the CoRoT view and the future|chapter=III.8 Exoplanets versus brown dwarfs: The CoRoT view and the future|year=2016|pages=157|doi=10.1051/978-2-7598-1876-1.c038|arxiv=1604.00917|isbn=978-2-7598-1876-1|s2cid=118434022}}</ref> based on a study of mass–density relationships.<ref>{{cite journal |arxiv=1506.05097|last1= Hatzes Heike Rauer|first1= Artie P.|title= A Definition for Giant Planets Based on the Mass-Density Relationship|year= 2015|doi=10.1088/2041-8205/810/2/L25|volume=810|issue= 2|journal=The Astrophysical Journal|page=L25|bibcode = 2015ApJ...810L..25H |s2cid= 119111221}}</ref> The [[Exoplanet Data Explorer]] includes objects up to 24 Jupiter masses with the advisory: "The 13 Jupiter-mass distinction by the IAU Working Group is physically unmotivated for planets with rocky cores, and observationally problematic due to the sin i ambiguity."<ref name="eod">{{cite journal| arxiv=1012.5676 |title=The Exoplanet Orbit Database|date=2010| bibcode = 2011PASP..123..412W |doi = 10.1086/659427| volume=123| issue=902|journal=Publications of the Astronomical Society of the Pacific| pages=412–422| last1=Wright|first1=J. T.| last2=Fakhouri|first2=O.|last3=Marcy|first3=G. W.| last4=Han| first4=E.| last5=Feng| first5=Y.| last6=Johnson| first6=John Asher| last7=Howard| first7=A. W.|  last8=Fischer|first8=D. A.|last9=Valenti |first9=J. A.| last10=Anderson| first10=J.| last11=Piskunov|first11=N.|s2cid=51769219}}</ref> The [[NASA Exoplanet Archive]] includes objects with a mass (or minimum mass) equal to or less than 30 Jupiter masses.<ref>{{Cite web|title=Exoplanet Criteria for Inclusion in the Exoplanet Archive|url=https://exoplanetarchive.ipac.caltech.edu/docs/exoplanet_criteria.html|access-date=2022-01-17|website=exoplanetarchive.ipac.caltech.edu}}</ref> Another criterion for separating planets and brown dwarfs, rather than deuterium fusion, formation process or location, is whether the core [[pressure]] is dominated by [[Coulomb barrier|Coulomb pressure]] or [[electron degeneracy pressure]] with the dividing line at around 5 Jupiter masses.<ref name="whatbasribrown">{{cite journal |doi=10.1146/annurev.earth.34.031405.125058 |journal=Annu. Rev. Earth Planet. Sci. |volume=34 |title=Planetesimals To Brown Dwarfs: What is a Planet? |pages=193–216 |date=2006 |arxiv=astro-ph/0608417 |bibcode=2006AREPS..34..193B|last1=Basri |first1=Gibor |last2=Brown |first2=Michael E. |s2cid=119338327 |url=https://authors.library.caltech.edu/5028/1/BASareps06.pdf |type=Submitted manuscript }}</ref><ref name=JamesLiebert>{{cite journal|bibcode=2003IAUS..211..529B|title=Nomenclature: Brown Dwarfs, Gas Giant Planets, and ?|last1=Liebert|first1=James|volume=211|date=2003|page=533|journal=Brown Dwarfs }}</ref>