HD 59686 Ab is an

exoplanet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

that orbits the giant star HD 59686 A in a close binary star system. It has a nearly circular orbit with a period of 300 days and a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of 1.09 AU, slightly greater than the distance between

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

and the Sun. It has a minimum mass 6.9 times that of Jupiter, with the true mass depending on the

orbital inclination Orbital inclination measures the tilt of an object's orbit around a celestial body. It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object. For a satellite orbiting the Earth ...

, which is not yet known. HD 59686 Ab was discovered by

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the temporal rate of change, rate of change of the distance or Slant range, range between the two points. It is e ...

and first announced in November 2003, but the discovery was not formally published until 2016. HD 59686, along with

Nu Octantis ν Octantis, Latinised as Nu Octantis, is a spectroscopic binary star in the constellation Octans with a period around 2.9 years. Its apparent magnitude is 3.73. Located around distant, the primary is an orange giant of spectral typ ...

, is one of the closest binary star systems known to host a planet orbiting a single star (i.e., not a

circumbinary planet A circumbinary planet is a planet that orbits two stars instead of one. The two stars orbit each other in a binary system, while the planet typically orbits farther from the center of the system than either of the two stars. In contrast, circums ...

), posing a challenge to theories of planet formation.

References

Gemini (constellation) Giant planets Exoplanets discovered in 2003 Exoplanets detected by radial velocity {{extrasolar-planet-stub