 An artist's impression of 47 Ursae Majoris b, depicting it as aJovian-like planet | |
| Discovery | |
|---|---|
| Discovered by | Marcy and Butleret al. |
| Discovery site |  United States |
| Discovery date | 17 January 1996 |
| Doppler spectroscopy | |
| Orbital characteristics | |
| Apastron | 2.17 ± 0.05 AU (324.6 ± 7.5 million km) |
| Periastron | 2.03 ± 0.05 AU (303.7 ± 7.5 million km) |
| 2.10 ± 0.02 AU (314.2 ± 3.0 million km)[1] | |
| Eccentricity | 0.032 ± 0.014[1] |
| 1,078 ± 2[1]d ~2.95y | |
Averageorbital speed | 21.3 ± 0.3 km/s |
| 2,451,917+63 −76[1] | |
| 334 ± 23[1] | |
| Semi-amplitude | 49.00 ± 0.87 m/s[2] |
| Star | 47 Ursae Majoris |
| Physical characteristics | |
| Temperature | 200 K |
47 Ursae Majoris b (abbreviated47 UMa b), formally namedTaphao Thong/təˌpaʊˈtɒŋ/,[3] is agas planet and anextrasolar planet approximately 46light-years from Earth in theconstellation ofUrsa Major.[4] The planet was discovered located in along-period orbit around thestar47 Ursae Majoris in January 1996 and as of 2011 it is the innermost of three known planets in itsplanetary system. It has amass at least 2.53 times that ofJupiter.
In July 2014 theInternational Astronomical Union launchedNameExoWorlds, a process for giving proper names to certain exoplanets and their host stars.[5] The process involved public nomination and voting for the new names.[6] In December 2015, the IAU announced the winning name was Taphao Thong (Thai:ตะเภาทอง[tā.pʰāw.tʰɔ̄ːŋ]) for this planet.[7] The winning name was submitted by the Thai Astronomical Society ofThailand. Taphaothong was one of two sisters associated with a Thai folk tale.[8]
Taphao Thong was discovered by detecting the changes in its star'sradial velocity as the planet'sgravity pulls the star around. This was achieved by observing theDoppler shift of thespectrum ofChalawan. After the discovery of the first extrasolar planet around a Sun-like star,Dimidium, astronomersGeoffrey Marcy andR. Paul Butler searched through their observational data for signs of extrasolar planets and soon discovered two: Taphao Thong and70 Virginis b. The discovery of Taphao Thong was announced in 1996.[9]
47 Ursae Majoris b orbits at a distance of 2.10AU from its star, taking 1,078 days or 2.95 years to complete arevolution.[1][4] It was the first long-period planet around amain sequence star to be discovered. Unlike the majority of known long-period extrasolar planets, theeccentricity 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. Preliminaryastrometric measurements made by theHipparcos satellite suggest the planet's orbit isinclined at an angle of 63.1° to the plane of the sky, which would imply atrue mass 12% greater than the lower limit determined by radial velocity measurements.[10] 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.[11]
Given the planet's high mass, it is likely that 47 Ursae Majoris b is agas giant with nosolid surface. Because the planet has only been detected indirectly, properties such as itsradius, composition andtemperature 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 tochemical equilibrium, the upper atmosphere of the planet is expected to contain water clouds, as opposed to theammonia clouds typical of Jupiter.[12]
Although 47 Ursae Majoris b is outside its star'shabitable zone, its gravitational influence would disrupt the orbit of planets in the outer part of the habitable zone.[13] In addition, it may have disrupted the formation ofterrestrial planets and reduced the delivery of water to any inner planets in the system.[14] 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.[15][16]
