 Artist's impression of 55 Cancri b. | |
| Discovery | |
|---|---|
| Discovered by | Butler,Marcy |
| Discovery site | California, USA |
| Discovery date | April 12, 1996 |
| Radial velocity | |
| Orbital characteristics | |
| Apastron | 0.116 AU (17,400,000 km) |
| Periastron | 0.113 AU (16,900,000 km) |
| 0.115 ± 0.0000011 AU (17,203,760 ± 160 km)[1] | |
| Eccentricity | 0.014 ± 0.008[1] |
| 14.65162 ± 0.0007[1]d 0.04011325y | |
| Inclination | ~85[2][3] |
| 2,450,002.94749 ± 1.2[1] | |
| 131.94 ± 30[1] | |
| Semi-amplitude | 71.32 ± 0.41[1] |
| Star | 55 Cancri A |
| Physical characteristics | |
| Mass | 0.824 ± 0.007[1][2]MJ |
55 Cancri b (abbreviated55 Cnc b), occasionally designated 55 Cancri Ab (to distinguish it from thestar55 Cancri B), formally namedGalileo, is anexoplanet orbiting theSun-like star55 Cancri A every 14.65days. It is the second planet in order of distance from its star, and is an example of ahot Jupiter, or possibly rather "warm Jupiter".[4]
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 Galileo for this planet.[7] The winning name was submitted by the Royal Netherlands Association for Meteorology and Astronomy of theNetherlands. It honors early-17th century astronomer and physicistGalileo Galilei.[8]
55 Cancri b was discovered in 1996 byGeoffrey Marcy andR. Paul Butler. It was the fourth known extrasolar planet, excludingpulsar planets. It was discovered by detecting variations in its star'sradial velocity caused by the planet'sgravity. By making sensitive measurements of theDoppler shift of thespectrum of 55 Cancri A, a 15-day periodicity was detected. The planet was announced in 1996, together with the planet ofTau Boötis and the innermost planet ofUpsilon Andromedae.[9]
Even when this inner planet, with amass at least 78% times that ofJupiter was accounted for, the star still showed a drift in its radial velocity. This eventually led to the discovery of the outer planet55 Cancri d in 2002.
55 Cancri b is in a short-period orbit, though not so extreme as that of the previously detected hot Jupiter51 Pegasi b. The orbital period indicates that the planet is located close to a 1:3mean motionresonance with55 Cancri c, however investigations of the planetary parameters in a Newtonian simulation indicate that while the orbital periods are close to this ratio, the planets are not actually in the resonance.[1]
In 2012, b's upper atmosphere was observed transiting the star; so its inclination is about 85 degrees, coplanar with55 Cancri e. This helped to constrain the mass of the planet but the inclination was too low to constrain its radius.[2]
The mass is about 0.85 that of Jupiter.[2]
55 Cancri b is agas giant with nosolid surface. The atmospheric transit has demonstratedhydrogen in the upper atmosphere.[2]
That transit is so tangential, that properties such as itsradius,density, andtemperature are unknown. Assuming a composition similar to that of Jupiter and that its environment is close tochemical equilibrium, 55 Cancri b's upperatmosphere is predicted to becloudless with aspectrum dominated byalkali metalabsorption.[10]
The atmosphere's transit indicates that it is slowly evaporating under the sun's heat. The evaporation is slower than that for previously studied (hotter) hot Jupiters.[4]
The planet is unlikely to have largemoons, sincetidal forces would either eject them from orbit or destroy them on short timescales relative to the age of the system.[11]
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