47 Ursae Majoris b (abbreviated 47 UMa b), formally named Taphao Thong , is a gas planet and an extrasolar planet approximately 46

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 from Earth 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 ...

of Ursa Major. The planet was discovered located in a long-period orbit around the

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 ...

47 Ursae Majoris 47 Ursae Majoris (abbreviated 47 UMa), formally named Chalawan , is a yellow dwarf star approximately 46 light-years from Earth in the constellation of Ursa Major. , three extrasolar planets (designated 47 Ursae Majoris b, c and d; t ...

in January 1996 and as of 2011 it is the innermost of three known planets in its

planetary system A planetary system is a set of gravitationally In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interacti ...

. It has a mass at least 2.53 times that of Jupiter.

Name

In July 2014 the International Astronomical Union launched NameExoWorlds, a process for giving proper names to certain exoplanets and their host stars. The process involved public nomination and voting for the new names. In December 2015, the IAU announced the winning name was Taphao Thong ( th, ตะเภาทอง ) for this planet. The winning name was submitted by the Thai Astronomical Society of Thailand. Taphaothong was one of two sisters associated with a Thai folk tale.

Discovery

Taphao Thong was discovered by detecting the changes in its star's

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 ...

as the planet's gravity pulls the star around. This was achieved by observing the

Doppler shift The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in frequency of a wave in relation to an observer who is moving relative to the wave source. It is named after the Austrian physicist Christian Doppler, who d ...

of the spectrum of Chalawan. After the discovery of the first extrasolar planet around a Sun-like star, Dimidium, astronomers Geoffrey Marcy and R. Paul Butler searched through their observational data for signs of extrasolar planets and soon discovered two: Taphao Thong and

70 Virginis b 70 Virginis b (abbreviated 70 Vir b) is an extrasolar planet approximately 60 light-years away in the constellation of Virgo. Announced in 1996 by Geoffrey Marcy and R. Paul Butler, 70 Virginis was one of the first stars confirmed to have plan ...

. The discovery of Taphao Thong was announced in 1996.

Orbit and mass

47 Ursae Majoris b orbits at a distance of 2.10 AU from its star, taking 1,078 days or 2.95 years to complete a revolution. It was the first long-period planet around a

main sequence In astronomy, the main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Her ...

star to be discovered. Unlike the majority of known long-period extrasolar planets, the eccentricity of the orbit of 47 Ursae Majoris b is low. A limitation of the radial velocity method used to detect 47 Ursae Majoris b is that only a lower limit on the planet's mass can be obtained. Preliminary astrometric measurements made by the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial obj ...

satellite suggest the planet's orbit is

inclined Incline, inclined, inclining, or inclination may refer to: *Grade (slope), the tilt, steepness, or angle from horizontal of a topographic feature (hillside, meadow, etc.) or constructed element (road, railway, field, etc.) *Slope, the tilt, steepn ...

at an angle of 63.1° to the plane of the sky, which would imply a true mass 12% greater than the lower limit determined by radial velocity measurements. However, subsequent investigation of the data reduction techniques used suggests that the Hipparcos measurements are not precise enough to adequately characterise the orbits of substellar companions, and the true inclination of the orbit (and hence the true mass) are regarded as unknown.

Physical characteristics

Given the planet's high mass, it is likely that 47 Ursae Majoris b is a gas giant with no solid surface. Because the planet has only been detected indirectly, properties such as its radius, composition and temperature are unknown. Due to its mass it is likely to have a surface gravity 6 to 8 times that of Earth. Assuming a composition similar to that of Jupiter and an environment close to chemical equilibrium, the upper atmosphere of the planet is expected to contain water clouds, as opposed to the ammonia clouds typical of Jupiter. Although 47 Ursae Majoris b is outside its star's habitable zone, its gravitational influence would disrupt the orbit of planets in the outer part of the habitable zone. In addition, it may have disrupted the formation of terrestrial planets and reduced the delivery of water to any inner planets in the system. Therefore, planets located in the habitable zone of 47 Ursae Majoris are likely to be small and dry. It has been theorized that light reflections and infrared emissions from 47 UMa b, along with tidal influence, could warm any moons in orbit around it to be habitable, despite the planet being outside the normally accepted habitable zone.

References

External links

* * * {{Sky, 10, 59, 28.0, +, 40, 25, 49, 45.9 47 Ursae Majoris Exoplanets discovered in 1996 Giant planets in the habitable zone Exoplanets detected by radial velocity Exoplanets with proper names