HD 139357 b
Encyclopedia
HD 139357 b is an extrasolar planet
located approximately 396 light years away in the constellation
of Draco
, orbiting the 6th magnitude
K-type giant
star
HD 139357
. It has a minimum mass
very massive, at nearly 10 times that of Jupiter, but its radius is unknown (probably no more than 1.2 Jupiters). This planet is probably most likely be a brown dwarf
if true mass
were to be known. The reason why true mass is unknown is due to its unknown inclination
. Follow up observations via direct imaging may determine its radius, hence density and surface gravity, and inclination to allow it to determine whether this object actually be a brown dwarf or a supermassive planet. As it is typical for supermassive planets, this orbits further from stars than Earth is from the Sun. The planet’s year is over three Earth years. However, the orbital eccentricity
of this planet is much greater than Earth, 0.1 vs 0.017. Like most known extrasolar planets, it was detected by a wobble method, which finds planet by studying wobbling motion of a star in circular motion caused by gravity of planets as they orbit the star. This detection took place on March 20, 2009, which was the first day of spring.
Extrasolar planet
An extrasolar planet, or exoplanet, is a planet outside the Solar System. A total of such planets have been identified as of . It is now known that a substantial fraction of stars have planets, including perhaps half of all Sun-like stars...
located approximately 396 light years away in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....
of Draco
Draco (constellation)
Draco is a constellation in the far northern sky. Its name is Latin for dragon. Draco is circumpolar for many observers in the northern hemisphere...
, orbiting the 6th magnitude
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...
K-type giant
Giant star
A giant star is a star with substantially larger radius and luminosity than a main sequence star of the same surface temperature. Typically, giant stars have radii between 10 and 100 solar radii and luminosities between 10 and 1,000 times that of the Sun. Stars still more luminous than giants are...
star
Star
A star is a massive, luminous sphere of plasma held together by gravity. At the end of its lifetime, a star can also contain a proportion of degenerate matter. The nearest star to Earth is the Sun, which is the source of most of the energy on Earth...
HD 139357
HD 139357
HD 139357 is a 6th magnitude K-type giant star located approximately 396 light years away in the constellation of Draco. Its mass is four thirds that of our Sun but its radius is 11.47 times larger...
. It has a minimum mass
Minimum mass
In astronomy, minimum mass is the lower-bound calculated mass of observed objects such as planets, stars and binary systems, nebulae, and black holes. Minimum mass is a widely cited statistic for extrasolar planets...
very massive, at nearly 10 times that of Jupiter, but its radius is unknown (probably no more than 1.2 Jupiters). This planet is probably most likely be a brown dwarf
Brown dwarf
Brown dwarfs are sub-stellar objects which are too low in mass to sustain hydrogen-1 fusion reactions in their cores, which is characteristic of stars on the main sequence. Brown dwarfs have fully convective surfaces and interiors, with no chemical differentiation by depth...
if true mass
True mass
The term true mass is synonymous with the term mass, but is used in astronomy to differentiate the measured mass of a planet from the lower limit of mass usually obtained from radial velocity techniques...
were to be known. The reason why true mass is unknown is due to its unknown inclination
Inclination
Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...
. Follow up observations via direct imaging may determine its radius, hence density and surface gravity, and inclination to allow it to determine whether this object actually be a brown dwarf or a supermassive planet. As it is typical for supermassive planets, this orbits further from stars than Earth is from the Sun. The planet’s year is over three Earth years. However, the orbital eccentricity
Orbital eccentricity
The orbital eccentricity of an astronomical body is the amount by which its orbit deviates from a perfect circle, where 0 is perfectly circular, and 1.0 is a parabola, and no longer a closed orbit...
of this planet is much greater than Earth, 0.1 vs 0.017. Like most known extrasolar planets, it was detected by a wobble method, which finds planet by studying wobbling motion of a star in circular motion caused by gravity of planets as they orbit the star. This detection took place on March 20, 2009, which was the first day of spring.