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55 Cancri b

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55 Cancri b
Extrasolar planet List of extrasolar planets
Parent star
Star 55 Cancri A
Constellation Cancer
Right ascension (α) 08h 52m 35.8s
Declination (δ) +28° 19′ 51″
Apparent magnitude (mV) 5.95
Distance 40.3 ± 0.4 ly
(12.3 ± 0.1 pc)
Spectral type G8V
Mass (m) 0.95 ± 0.10 M
Radius (r) 1.152 ± 0.035 R
Temperature (T) 5373 ± 9.7 K
Metallicity [Fe/H] 0.29
Age 7.4–8.7 Gyr
Orbital elements
Semimajor axis (a) 0.115 ± 0.0000011[1] AU
(17.2 Gm)
    9.18 mas
Periastron (q) 0.113 AU
(16.9 Gm)
Apastron (Q) 0.116 AU
(17.4 Gm)
Eccentricity (e) 0.014 ± 0.008[1]
Orbital period (P) 14.65162 ± 0.0007[1] d
(0.04011325 y)
Inclination (i) ~85[2][3]°
Argument of
(ω) 131.94 ± 30[1]°
Time of periastron (T0) 2,450,002.94749 ± 1.2[1] JD
Semi-amplitude (K) 71.32 ± 0.41[1] m/s
Physical characteristics
Mass (m) 0.824 ± 0.007[1][2] MJ
Stellar flux (F) 48
Discovery information
Discovery date April 12, 1996
Discoverer(s) Butler, Marcy
Discovery method Radial velocity
Other detection methods Transit
Discovery site California, USA
Discovery status Published
Other designations
55 Cancri Ab, Rho1 Cancri b, HD 75732 b
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data
Simulation of the extrasolar planet 55 Cancri b.

55 Cancri b (abbreviated 55 Cnc b and 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 14.65 days. It is the second planet in order of distance from its star, and is an example of a hot Jupiter, or possibly rather "warm Jupiter".[4] Discovered in 1996 by Geoffrey Marcy and R. Paul Butler, 55 Cancri b was the fourth known extrasolar planet, excluding pulsar planets.


The radial velocity trend of 55 Cancri caused by the presence of 55 Cancri b.

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.[5]

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[edit]

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 orbital period indicates that the planet is located close to a 1:3 mean motion resonance with 55 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 with 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 .85 that of Jupiter.[2]


55 Cancri b is a gas giant with no solid surface. The atmospheric transit has demonstrated hydrogen in the upper atmosphere.[2]

That transit is so tangential, that properties such as its radius, density, and temperature are unknown. Assuming a composition similar to that of Jupiter and that its environment is close to chemical equilibrium, 55 Cancri b's upper atmosphere is predicted to be cloudless with a spectrum dominated by alkali metal absorption.[6]

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 large moons, since tidal forces would either eject them from orbit or destroy them on short timescales relative to the age of the system.[7]

See also[edit]


  1. ^ a b c d e f g h DA Fischer et al. (March 2008). "Five Planets Orbiting 55 Cancri". Astrophysical Journal 675 (675): 790–801. arXiv:0712.3917. Bibcode:2008ApJ...675..790F. doi:10.1086/525512. 
  2. ^ a b c d e D. Ehrenreich et al. (October 2, 2012). "Hint of a transiting extended atmosphere on 55 Cancri b". Astronomy & Astrophysics. arXiv:1210.0531. Bibcode:2012A&A...547A..18E. doi:10.1051/0004-6361/201219981. 
  3. ^ D. Dragomir, 2012-08-27, referred to in Ehrenreich
  4. ^ a b "Astrophile: First puffy, 'warm Jupiter' spotted - space - 12 October 2012". New Scientist. Retrieved 2012-11-09. 
  5. ^ Butler; Marcy, Geoffrey W.; Williams, Eric; Hauser, Heather; Shirts, Phil et al. (1997). "Three New 51 Pegasi-Type Planets". The Astrophysical Journal 474 (2): L115–L118. Bibcode:1997ApJ...474L.115B. doi:10.1086/310444. 
  6. ^ Sudarsky, D. et al. (2003). "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets". The Astrophysical Journal 588 (2): 1121–1148. arXiv:astro-ph/0210216. Bibcode:2003ApJ...588.1121S. doi:10.1086/374331. 
  7. ^ Barnes, J.; O'Brien, D. (2002). "Stability of Satellites around Close-in Extrasolar Giant Planets". The Astrophysical Journal 575 (2): 1087–1093. arXiv:astro-ph/0205035. Bibcode:2002ApJ...575.1087B. doi:10.1086/341477. 

External links[edit]

Coordinates: Sky map 08h 52m 35.8s, +28° 19′ 51″