Circumtriple planet

{{Short description|Planet that orbits three stars}}

File:GW Orionis 1.jpg star system. Scientists have observed abnormalities in the behavior patterns of the three stars and have speculated that an unseen planet may be orbiting all three stars simultaneously.]]

A circumtriple planet is a celestial mass that is hypothesized to be orbiting not only a single star but three stars at the same time. Scientists observing the star system GW Ori, which is a huge disk of dust and gases about 1,300 light years away from Earth, suspect that there may be a circumtriple planet orbiting the three stars. They observed a gap in the vast dust cloud and they hypothesize that there may be a planet in this gap. The planet itself has not been seen but its influence may explain gravitational oddities within the star system. By using computer modeling, some scientists believe that a Jupiter-sized planet may be able to explain the star system's rings and strange behavior, according to one account. If so, this may be the first known example of a circumtriple planet in the universe.

In 2015, the planet or brown dwarf, 2MASS J0019-6226 was found to orbit the three stars in the HIP 1481 system. It is believed to be about 15 times the mass of Jupiter and is roughly 155,000 au away. 2MASS J0019-6226 has a size of about {{Jupiter radius|1.6}}. If it is a planet, it would be the first confirmed circumtriple planet and the planet with the largest semi-major axis.{{Cite EPE|name=2MASS J0019-6226|id=10798|access-date=2025-03-23}}{{cite journal |last=Faherty |first=Jacqueline |date=2016 |title=Population Properties of Brown Dwarf Analogs to Exoplanets |journal=The Astrophysical Journal Supplement Series |volume=225 |issue=1 |page=10 |doi=10.3847/0067-0049/225/1/10 |doi-access=free |arxiv=1605.07927 |bibcode=2016ApJS..225...10F }}

In 2022, evidence of a very small planet was found around the triple system PSR J0337+1715.{{cite arXiv |eprint=2205.09345 |last1=Voisin |first1=Guillaume |last2=Luth |first2=G. |last3=Cognard |first3=I. |last4=Freire |first4=P. |last5=Wex |first5=N. |last6=Guillemot |first6=L. |last7=Desvignes |first7=G. |last8=Kramer |first8=M. |last9=Theureau |first9=G. |last10=Saillenfest |first10=M. |title=One pulsar, two white dwarfs, and a planet confirming the strong equivalence principle |date=2022 |class=astro-ph.HE }} In 2024, additional data allowed the planet's mass to be constrained to {{val|0.0041|0.003|ul=Earth mass}}, making it one of the smallest objects directly detected outside the Solar System so far.{{cite journal |arxiv=2411.10066 |doi=10.1051/0004-6361/202452100 |title=Explanation of the exceptionally strong timing noise of PSR J0337+1715 by a circum-ternary planet and consequences for gravity tests |date=2025 |last1=Voisin |first1=G. |last2=Cognard |first2=I. |last3=Saillenfest |first3=M. |last4=Tauris |first4=T. M. |last5=Wex |first5=N. |last6=Guillemot |first6=L. |last7=Theureau |first7=G. |last8=Freire |first8=P. C. C. |last9=Kramer |first9=M. |journal=Astronomy & Astrophysics |volume=693 |pages=A143 |bibcode=2025A&A...693A.143V }}

In 2024, the substellar object CWISE J235827.96–521813.4 was detected to be bound to the Gliese 900 triple star system at a distance of {{val|12000|ul=AU}},{{Cite journal |last1=Rothermich |first1=Austin |last2=Faherty |first2=Jacqueline K. |last3=Bardalez-Gagliuffi |first3=Daniella |last4=Schneider |first4=Adam C. |last5=Kirkpatrick |first5=J. Davy |last6=Meisner |first6=Aaron M. |last7=Burgasser |first7=Adam J. |last8=Kuchner |first8=Marc |last9=Allers |first9=Katelyn |last10=Gagné |first10=Jonathan |last11=Caselden |first11=Dan |last12=Calamari |first12=Emily |last13=Popinchalk |first13=Mark |last14=Suárez |first14=Genaro |last15=Gerasimov |first15=Roman |date=2024-06-01 |title=89 New Ultracool Dwarf Comoving Companions Identified with the Backyard Worlds: Planet 9 Citizen Science Project |journal=The Astronomical Journal |volume=167 |issue=6 |pages=253 |doi=10.3847/1538-3881/ad324e |doi-access=free |issn=0004-6256|arxiv=2403.04592 |bibcode=2024AJ....167..253R }} thus becoming the planet with the longest orbital period and first confirmed circumtriple planet.

Circumtriple planets are likely to be an extremely rare phenomenon in the universe. Studying them could add to human understanding of how planets form.