Circumtriple planet

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.^[1] Scientists observing the star system GW Ori, which is a large 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.^[2] They observed a gap in the vast dust cloud and they hypothesize that there may be a planet in this gap.^[2] The planet itself has not been seen but its influence may explain gravitational oddities within the star system.^[3] 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.^[4] If so, this may be the first known example of a circumtriple planet in the universe.^[4]

Schematic diagram showing a proposed geometry of the GW Orionis 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.

In 2022, tentative evidence of a very small planet was found around the triple system PSR J0337+1715.^[5] In 2024, additional data allowed the planet's mass to be constrained to 0.0041±0.003 M_🜨, making it one of the smallest objects directly detected outside the Solar System so far.^[6]

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 12000 AU,^[7] thus becoming the planet with the longest orbital period and first confirmed circumtriple planet.

Circumtriple planets are likely to be a very rare phenomenon in the universe.^[4] Studying them could add to human understanding of how planets form.^[3]

Fiction

A circumtriple planet is prominently featured in the Remembrance of Earth's Past book series. In the series, the planet of Trisolaris orbits a three-star system, and the chaotic nature of the system drives the native species of the planet to seek refuge on Earth, which has a comparatively more "stable" one-star system.^[8]