HD 139357 b is a very massive extrasolar planet or

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...

located approximately 390

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away, orbiting the 6th magnitude K-type giant

star A star is an astronomical object comprising a luminous spheroid of plasma (physics), plasma held together by its gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many other stars are visible to the naked ...

HD 139357 in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms Asterism (astronomy), a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the e ...

Draco Draco is the Latin word for serpent or dragon. Draco or Drako may also refer to: People * Draco (lawgiver) (from Greek: Δράκων; 7th century BC), the first lawgiver of ancient Athens, Greece, from whom the term ''draconian'' is derived * D ...

. The detection occurred on March 20, 2009, which was the first day of spring. The actual mass and radius of this body remain uncertain, but it has a minimum mass of nearly 10 times that of Jupiter and a radius of probably no more than 1.2 times Jupiter's. Most likely this is a

rather than a planet. The reason why the object's true mass was initially unknown is due to the undetermined

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

of its orbital plane. Follow up observations via direct imaging may determine its radius and orbital inclination, thereby giving its density and surface gravity, which will allow a determination as to whether this object is a brown dwarf or a supermassive planet. A 2022 study estimated the true mass of HD 139357 b at about via

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. His ...

, although this estimate is poorly constrained. If this is the true mass, the object would be a

. As it is typical for supermassive planets, this orbits further from its host star than Earth is from the Sun. The planet's year is over three Earth years. However, the

orbital eccentricity In astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values betwee ...

of this object is much greater than Earth's: 0.1 vs. 0.017. Like most known extrasolar planets, it was detected by the wobble method, which detects planets through the circular wobbling motion of the star caused by the gravity of orbiting body.

References

Exoplanets discovered in 2009 Giant planets Draco (constellation) Exoplanets detected by radial velocity Exoplanets detected by astrometry {{extrasolar-planet-stub

See also

References