Habitability of binary star systems

<h2 id="non-circumbinary-planet-s-type">Non-circumbinary planet (S-Type)</h2>
In non-<a href="/facts/Circumbinary_planet/3Tpw768E">circumbinary planets</a>, if a planet's distance to its primary exceeds about one fifth of the closest approach of the other star, orbital stability is not guaranteed.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> Whether planets might form in binaries at all had long been unclear, given that gravitational forces might interfere with planet formation. Theoretical work by <a href="/facts/Alan_Boss/D14wq4aw">Alan Boss</a> at the <a href="/facts/Carnegie_Institution/zS5MqNUP">Carnegie Institution</a> has shown that gas giants can form around stars in binary systems much as they do around solitary stars.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a>
Studies of <a href="/facts/Alpha_Centauri/6BlySfIj">Alpha Centauri</a>, the nearest star system to the Sun, suggested that binaries need not be discounted in the search for habitable planets. Centauri A and B have an 11 au distance at closest approach (23 au mean), and both have stable habitable zones.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> A study of long-term orbital stability for simulated planets within the system shows that planets within approximately three au of either star may remain stable (i.e. the <a href="/facts/Semi-major_axis/l7JES2wo">semi-major axis</a> deviating by less than 5%). The habitable zone for Alpha Centauri A extends, conservatively estimated, from 1.37 to 1.76 au<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> and that of Alpha Centauri B from 0.77 to 1.14 au<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>—well within the stable region in both cases.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>

<h2 id="circumbinary-planet-p-type">Circumbinary planet (P-Type)</h2>
For a <a href="/facts/Circumbinary_planet/3Tpw768E">circumbinary planet</a>, orbital stability is guaranteed only if the planet's distance from the stars is significantly greater than star-to-star distance.
The minimum stable star-to-circumbinary-planet separation is about 2–4 times the binary star separation, or <a href="/facts/Orbital_period/94f56uh2">orbital period</a> about 3–8 times the binary period. The innermost planets in all the Kepler circumbinary systems have been found orbiting close to this radius. The planets have <a href="/facts/Semi-major_axis/l7JES2wo">semi-major axes</a> that lie between 1.09 and 1.46 times this critical radius. The reason could be that <a href="/facts/Planetary_migration/rH6cEwNR">migration</a> might become inefficient near the critical radius, leaving planets just outside this radius.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
For example, <a href="/facts/Kepler-47c/aorHy4u8">Kepler-47c</a> is a <a href="/facts/Gas_giant/pmF6KztG">gas giant</a> in the circumbinary habitable zone of the <a href="/facts/Kepler-47/A7TqmUpW">Kepler-47</a> system.
If Earth-like planets form in or migrate into the circumbinary habitable zone, they would be capable of sustaining liquid water on their surface in spite of the dynamical and radiative interaction with the binary stars.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a>
The limits of stability for S-type and P-type orbits within binary as well as trinary stellar systems have been established as a function of the orbital characteristics of the stars, for both prograde and retrograde motions of stars and planets.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a>

<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Astrobiology/GS1tFhrf">Astrobiology</a></li>
<li><a href="/facts/Circumstellar_habitable_zone/bjgaUkfB">Circumstellar habitable zone</a></li>
<li><a href="/facts/Habitability_of_yellow_dwarf_systems/uVLH4eCJ">Habitability of yellow dwarf systems</a></li>
<li><a href="/facts/Planetary_habitability/n8A0ehR8">Planetary habitability</a></li>
<li><a href="/facts/Circumbinary_planet/3Tpw768E">Circumbinary planet</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">"Earth-Sized 'Tatooine' Planets Could Be Habitable" (Press release). NASA Jet Propulsion Laboratory, California Institute of Technology. April 2017. Archived from the original on 2019-06-19. Retrieved 2018-12-15. <a href="https://www.jpl.nasa.gov/news/news.php?feature=6811" target="_blank">https://www.jpl.nasa.gov/news/news.php?feature=6811</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Eggl, Siegfried (2018). "Habitability of Planets in Binary Star Systems". In Deeg, Hans J.; Belmonte, Juan Antonio (eds.). Handbook of Exoplanets. Cham: Springer International Publishing. pp. 1–27. Bibcode:2018haex.bookE..61E. doi:10.1007/978-3-319-30648-3_61-1. ISBN 978-3-319-30648-3. <a href="978-3-319-30648-3" target="_blank">978-3-319-30648-3</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">"Most Milky Way Stars Are Single" (Press release). Harvard-Smithsonian Center for Astrophysics. January 30, 2006. Archived from the original on 2007-08-13. Retrieved 2007-06-05. <a href="https://web.archive.org/web/20070813062958/http://cfa-www.harvard.edu/press/2006/pr200611.html" target="_blank">https://web.archive.org/web/20070813062958/http://cfa-www.harvard.edu/press/2006/pr200611.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">V. Quintana, Elisa; J. Lissauer, Jack (2007). "Terrestrial Planet Formation in Binary Star Systems". Extreme Solar Systems. 398: 201. arXiv:0705.3444. Bibcode:2008ASPC..398..201Q. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"Stars and Habitable Planets". www.solstation.com. Sol Company. Archived from the original on 2011-06-28. Retrieved 2007-06-05. <a href="http://www.solstation.com/habitable.htm" target="_blank">http://www.solstation.com/habitable.htm</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">"Planetary Systems can from around Binary Stars" (Press release). Carnegie Institution. January 2006. Archived from the original on 2011-05-15. Retrieved 2007-06-05. <a href="https://web.archive.org/web/20110515225714/http://carnegieinstitution.org/news_releases/news_0601_10.html" target="_blank">https://web.archive.org/web/20110515225714/http://carnegieinstitution.org/news_releases/news_0601_10.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Eggl, Siegfried (2018). "Habitability of Planets in Binary Star Systems". In Deeg, Hans J.; Belmonte, Juan Antonio (eds.). Handbook of Exoplanets. Cham: Springer International Publishing. pp. 1–27. Bibcode:2018haex.bookE..61E. doi:10.1007/978-3-319-30648-3_61-1. ISBN 978-3-319-30648-3. <a href="978-3-319-30648-3" target="_blank">978-3-319-30648-3</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Eggl, Siegfried; Haghighipour, Nader; Pilat-Lohinger, Elke (January 2013). "Detectability of Earth-like planets in circumstellar habitable zones of binary star systems with sun-like components". The Astrophysical Journal. 764 (2): 130. arXiv:1212.4884. Bibcode:2013ApJ...764..130E. doi:10.1088/0004-637X/764/2/130. ISSN 0004-637X. S2CID 31934602. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Eggl, Siegfried (2018). "Habitability of Planets in Binary Star Systems". In Deeg, Hans J.; Belmonte, Juan Antonio (eds.). Handbook of Exoplanets. Cham: Springer International Publishing. pp. 1–27. Bibcode:2018haex.bookE..61E. doi:10.1007/978-3-319-30648-3_61-1. ISBN 978-3-319-30648-3. <a href="978-3-319-30648-3" target="_blank">978-3-319-30648-3</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Eggl, Siegfried (2018). "Habitability of Planets in Binary Star Systems". In Deeg, Hans J.; Belmonte, Juan Antonio (eds.). Handbook of Exoplanets. Cham: Springer International Publishing. pp. 1–27. Bibcode:2018haex.bookE..61E. doi:10.1007/978-3-319-30648-3_61-1. ISBN 978-3-319-30648-3. <a href="978-3-319-30648-3" target="_blank">978-3-319-30648-3</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Wiegert, Paul A.; Holman, Matt J. (April 1997). "The Stability of Planets in the Alpha Centauri System". The Astronomical Journal. 113 (4): 1445. arXiv:astro-ph/9609106. Bibcode:1997AJ....113.1445W. doi:10.1086/118360. S2CID 18969130. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Welsh, William F.; Orosz, Jerome A.; Carter, Joshua A.; Fabrycky, Daniel C.; the Kepler Team (August 2012). "Recent Kepler Results On Circumbinary Planets". Proceedings of the International Astronomical Union. 8 (S293): 125–132. arXiv:1308.6328. doi:10.1017/S1743921313012684. ISSN 1743-9213. S2CID 119230654. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Popp, Max; Eggl, Siegfried (April 2017). "Climate variations on Earth-like circumbinary planets". Nature Communications. 8 (1): 14957. Bibcode:2017NatCo...814957P. doi:10.1038/ncomms14957. ISSN 2041-1723. PMC 5384241. PMID 28382929. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5384241" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5384241</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Busetti, F.; Beust, H.; Harley, C. (November 2018). "Stability of planets in triple star systems". Astronomy & Astrophysics. 619: A91. arXiv:1811.08221. Bibcode:2018A&A...619A..91B. doi:10.1051/0004-6361/201833097. ISSN 0004-6361. S2CID 119477324. <a href="/wiki/ArXiv_(identifier)" target="_blank">/wiki/ArXiv_(identifier)</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
</ol>

Habitability of binary star systems open-in-new

Habitability of binary star systems