55 Cancri b
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55 Cancri b (occasionally referred to as 55 Cancri Ab in order to distinguish it from the star 55 Cancri B) is an extrasolar planet orbiting the Sun-like star 55 Cancri A every 14.7 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter. Discovered in 1996 by Geoffrey Marcy and R. Paul Butler, 55 Cancri b was the fourth known extrasolar planet, excluding pulsar planets.
Discovery
Like the majority of known extrasolar planets, 55 Cancri b was discovered by detecting variations in its star's radial velocity caused by the planet's gravity. By making sensitive measurements of the Doppler shift of the spectrum of 55 Cancri A, a 15-day periodicity was detected. The planet was announced in 1996, together with the planet of Tau Boötis and the innermost planet of Upsilon Andromedae.[1]
Even when this inner planet, with a mass at least 78% times that of Jupiter was accounted for, the star still showed a drift in its radial velocity. This eventually led to the discovery of the outer planet 55 Cancri d in 2002.
Orbit and mass
55 Cancri b is in a short-period orbit, though not so extreme as that of the previously detected hot Jupiter 51 Pegasi b. The planet is in a 1:3 orbital resonance with the nearby planet 55 Cancri c.[2]
A limitation of the radial velocity method used to discover the planet is that only a lower limit on the mass can be determined. Astrometric measurements made with the Hubble Space Telescope suggest that the outer planet is inclined at around 53° with respect to the plane of the sky.[3] Assuming this measurement is correct and the planetary system is coplanar, the planet's true mass is 25% greater than the lower limit, at around 0.98 Jupiter mass.
Characteristics
Given the planet's high mass, it is likely that 55 Cancri b is a gas giant with no solid surface. Since the planet has only been detected indirectly, properties such as its radius, composition and temperature are unknown. Assuming a composition similar to that of Jupiter and that its environment is close to chemical equilibrium, 55 Cancri b is predicted to have a cloudless upper atmosphere with a spectrum dominated by alkali metal absorption.[4]
The planet is unlikely to have large moons, since tidal forces would either eject them from orbit or destroy them on short timescales relative to the age of the system.[5]
References
- ^ Butler, R.; et al. (1997). "Three New 51 Pegasi-Type Planets". The Astrophysical Journal. 474: L115–L118.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Jianghui, J.; et al. (2003). "Could the 55 Cancri Planetary System Really Be in the 3:1 Mean Motion Resonance?". The Astrophysical Journal. 585: L139–L142.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ McArthur; et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope". The Astrophysical Journal. 614: L81–L84.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Sudarsky, D.; et al. (2003). "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets". The Astrophysical Journal. 588 (2): 1121–1148.
{{cite journal}}: Explicit use of et al. in:|author=(help) - ^ Barnes, J., O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal. 575 (2): 1087–1093.
{{cite journal}}: CS1 maint: multiple names: authors list (link)
See also
External links
- SIMBAD: * 55 Cnc b -- Extra-solar Planet Candidate
- The Extrasolar Planets Encyclopaedia: Notes for Planet 55 Cnc b
- Extrasolar Visions: 55 Cancri b
