Editing Binary star (section)

====Planets====
{{main|Habitability of binary star systems}}
[[File:Planets in binary star systems - P- and S-type.svg|thumb|Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit]]

While a number of binary star systems have been found to harbor [[extrasolar planets]], such systems are comparatively rare compared to single star systems. Observations by the [[Kepler space telescope]] have shown that most single stars of the same type as the [[Sun]] have plenty of planets, but only one-third of binary stars do. According to theoretical simulations,<ref>{{cite journal | bibcode = 2017AAS...22921905K | title=The Ruinous Influence of Close Binary Companions on Planetary Systems | journal=American Astronomical Society Meeting Abstracts #229 | volume=229 | pages=219.05 | year=2017 | author1=Kraus, Adam L. |author2=Ireland, Michael |author3=Mann, Andrew |author4=Huber, Daniel |author5=Dupuy, Trent J.}}</ref> even widely separated binary stars often disrupt the discs of rocky grains from which [[protoplanets]] form. On the other hand, other simulations suggest that the presence of a binary companion can actually improve the rate of planet formation within stable orbital zones by "stirring up" the protoplanetary disk, increasing the accretion rate of the protoplanets within.<ref name="formation"/>

Detecting planets in multiple star systems introduces additional technical difficulties, which may be why they are only rarely found.<ref>{{cite news | url = http://www.space.com/scienceastronomy/050517_binary_stars.html | title = Planets with Two Suns Likely Common | first = M | last = Schirber | publisher = Space.com | date = 17 May 2005}}</ref> Examples include the [[white dwarf]]-[[pulsar]] binary [[PSR B1620-26]], the [[subgiant]]-[[red dwarf]] binary [[Gamma Cephei]], and the [[white dwarf]]-[[red dwarf]] binary [[NN Serpentis]], among others.<ref>More circumbinary planets are listed in: {{Cite journal |arxiv=1010.4048 |author1=Muterspaugh |author2=Lane |author3=Kulkarni |author4=Maciej Konacki |author5=Burke |author6=Colavita |author7=Shao |author8=Hartkopf |author9=Boss |title=The PHASES Differential Astrometry Data Archive. V. Candidate Substellar Companions to Binary Systems |journal=The Astronomical Journal |volume=140 |issue=6 |pages=1657 |date=2010 |doi=10.1088/0004-6256/140/6/1657 |bibcode=2010AJ....140.1657M |s2cid=59585356}}</ref>

A study of fourteen previously known planetary systems found three of these systems to be binary systems. All planets were found to be in S-type orbits around the primary star. In these three cases the secondary star was much dimmer than the primary and so was not previously detected. This discovery resulted in a recalculation of parameters for both the planet and the primary star.<ref name="exobinary">{{cite journal
| url=http://www.mpia.de/homes/henning/Publications/daemgen.pdf
| title=Binarity of transit host stars – Implications for planetary parameters
| date=2009
| volume=498
| issue=2
| pages=567–574
| last1=Daemgen | first1=S.
| journal=[[Astronomy and Astrophysics]]
| doi=10.1051/0004-6361/200810988
| last2=Hormuth
| first2=F.
| last3=Brandner
| first3=W.
| last4=Bergfors
| first4=C.
| last5=Janson
| first5=M.
| last6=Hippler
| first6=S.
| last7=Henning
| first7=T.
| bibcode=2009A&A...498..567D
| arxiv=0902.2179
| s2cid=9893376
}}</ref>

[[Science fiction]] has often featured [[planet]]s of binary or ternary stars as a setting, for example, George Lucas' [[Tatooine]] from ''[[Star Wars]]'', and one notable story, "[[Nightfall (Asimov short story)|Nightfall]]", even takes this to a six-star system. In reality, some orbital ranges are impossible for dynamical reasons (the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range), whilst other orbits present serious challenges for eventual [[biosphere]]s because of likely extreme variations in surface temperature during different parts of the orbit. Planets that orbit just one star in a binary system are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or "[[Circumbinary planet|circumbinary]]" orbits. It is estimated that 50–60% of binary systems are capable of supporting habitable terrestrial planets within stable orbital ranges.<ref name="formation">{{cite journal |title=Terrestrial Planet Formation in Binary Star Systems |journal=Extreme Solar Systems |volume=398 |pages=201 |author=Elisa V. Quintana |author2=Jack J. Lissauer |date=2007 |arxiv=0705.3444 |bibcode=2008ASPC..398..201Q}}</ref>