{{Short description|Extrasolar planet in the constellation Draco}} {{Infobox planet | name = [[Henry Draper catalogue|HD]] 139357 b <!-- DISCOVERY --> | discoverer = Doellinger et al.<ref name="Döllinger2009"/> | discovery_site = TLS | discovered = March 20, 2009 | discovery_method = [[radial velocity method|radial velocity]] <!-- DESIGNATIONS --> <!-- ORBITAL --> | apsis = astron | aphelion = {{convert|2.60|AU|km|abbr=on}} | perihelion = {{convert|2.12|AU|km|abbr=on}} | semimajor = {{convert|2.36|±|0.2|AU|km|abbr=on}} | eccentricity = 0.1 ± 0.02 | period = 1125.7 ± 9 [[day|d]]<br>3.0819 ± 0.0246 [[year|y]] | time_periastron = 2452466.7 ± 3.2 | arg_peri = 235.4 ± 10.6 | star = [[HD 139357]] <!-- PHYS CHARS --> <!-- ATMOSPHERE --> <!-- NOTES --> }} '''HD 139357 b''' is a very massive [[extrasolar planet]] or [[brown dwarf]] located approximately 390 [[light year]]s away, orbiting the 6th [[apparent magnitude|magnitude]] [[K-type star|K-type]] [[giant star|giant]] [[star]] [[HD 139357]] in the [[constellation]] of [[Draco (constellation)|Draco]]. The detection occurred on March 20, 2009, which was the first day of spring.
The actual mass and radius of this body remain uncertain, but it has a [[minimum mass]] of nearly 10 times that of Jupiter and a radius of probably no more than 1.2 times Jupiter's. Most likely this is a [[brown dwarf]] rather than a planet. The reason why the object's [[true mass]] was initially unknown is due to the undetermined [[inclination]] of its orbital plane. Follow up observations via direct imaging may determine its radius and orbital inclination, thereby giving its density and surface gravity, which will allow a determination as to whether this object is a brown dwarf or a supermassive planet.
A 2022 study estimated the true mass of HD 139357 b at about {{Jupiter mass|16.38}} via [[astrometry]], although this estimate is poorly constrained. If this is the true mass, the object would be a [[brown dwarf]].<ref name="Feng2022"/>
As it is typical for supermassive planets, this orbits further from its host star than Earth is from the Sun. The planet's year is over three Earth years. However, the [[orbital eccentricity]] of this object is much greater than Earth's: 0.1 vs. 0.017. Like most known extrasolar planets, it was detected by the [[wobble method]], which detects planets through the circular wobbling motion of the star caused by the gravity of orbiting body.
== See also == * [[42 Draconis b]] * [[Iota Draconis b]]
== References == {{Reflist|refs=
<ref name="Döllinger2009">{{cite journal | title=Planetary companion candidates around the K giant stars 42 Draconis and HD 139 357 | url=http://www.aanda.org/articles/aa/full_html/2009/21/aa10837-08/aa10837-08.html | last1=Döllinger | first1=M. P. | last2=Hatzes | first2=A. P. | last3=Pasquini | first3=L. | last4=Guenther | first4=E. W. | last5=Hartmann | first5=M. | last6=Girardi | first6=L. | display-authors=1 | journal=Astronomy and Astrophysics | volume=499 | issue=3 | pages=935–942 | date=2009 | arxiv=0903.3593 | bibcode=2009A&A...499..935D | doi=10.1051/0004-6361/200810837 | s2cid=15677079 }}</ref>
<ref name="Feng2022">{{cite journal |last1=Feng |first1=Fabo |last2=Butler |first2=R. Paul |display-authors=etal |date=August 2022 |title=3D Selection of 167 Substellar Companions to Nearby Stars |journal=[[The Astrophysical Journal Supplement Series]] |volume=262 |issue=21 |page=21 |doi=10.3847/1538-4365/ac7e57 |arxiv=2208.12720 |bibcode=2022ApJS..262...21F|s2cid=251864022 |doi-access=free }}</ref>
}}
{{Draco (constellation)}} {{Sky|15|35|16.1992|+|53|55|19.717|396}}
{{DEFAULTSORT:HD 139357 b}} [[Category:Exoplanets discovered in 2009]] [[Category:Giant planets]] [[Category:Draco (constellation)]] [[Category:Exoplanets detected by radial velocity]] [[Category:Exoplanets detected by astrometry]]