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55 Cancri d

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55 Cancri d

55 Cancri d
Exoplanet List of exoplanets

Radial velocity changes over time of 55 Cancri caused by the orbit of 55 Cancri d.
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
Semi-major axis (a) 5.77 ± 0.11[1] AU
(863 Gm)
    462 mas
Periastron (q) 5.63 AU
(842 Gm)
Apastron (Q) 5.92 AU
(885 Gm)
Eccentricity (e) 0.025 ± 0.03[1]
Orbital period (P) 5218 ± 230[1] d
(14.29 y)
Argument of
(ω) 181.3 ± 32[1]°
Time of periastron (T0) 2,452,500.6 ± 230[1] JD
Semi-amplitude (K) 46.85 ± 1.8[1] m/s
Physical characteristics
Minimum mass (m sin i) 3.835 ± 0.08[1] MJ
Stellar flux (F) 0.019
Discovery information
Discovery date June 13, 2002
Discoverer(s) Marcy et al.
Discovery method Radial velocity
Discovery site California, USA
Discovery status Published
Other designations
55 Cancri Ad, Rho1 Cancri d, HD 75732 d
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

55 Cancri d (abbreviated 55 Cnc d) is an extrasolar planet in a long-period orbit around the Sun-like star 55 Cancri A. Located at a similar distance from its star as Jupiter is from our Sun, it is the fifth and outermost known planet in its planetary system. 55 Cancri d was discovered on June 13, 2002.

The planet and its host star is one of the planetary systems selected by the International Astronomical Union as part of their public process for giving proper names to exoplanets and their host star (where no proper name already exists).[2][3] The process involves public nomination and voting for the new names, and the IAU plans to announce the new names in mid-November 2015.[4]


  • Discovery 1
  • Orbit and mass 2
  • Characteristics 3
  • See also 4
  • References 5
  • External links 6


Like the majority of known extrasolar planets, 55 Cancri d was detected by observing changes in its star's radial velocity. This was achieved by making sensitive measurements of the Doppler shift of the star's spectrum. At the time of discovery, 55 Cancri A was already known to possess one planet (55 Cancri b), however there was still a drift in the radial velocity measurements which was unaccounted-for.[5]

In 2002, further measurements revealed the presence of a long-period planet in an orbit at around 5 AU from the star.[6] The same measurements also indicated the presence of another inner planet, designated 55 Cancri c.

Orbit and mass

55 Cnc d's orbit would be outside of Jupiter's orbit at 5.2AU.

When 55 Cancri d was discovered, it was thought to be on a fairly low eccentricity orbit similar to Jupiter in our solar system, though the orbital elements were not well determined.[6] As more data were collected, the best-fit solution for this planet turned out to be highly eccentric, more so than any of the planets in our solar system (including Pluto).[7] In 2008, after a complete orbit of this planet had been observed, the true orbit was revealed, indicating that as had been originally suspected, the planet's 14 year orbit was in fact near-circular, located about 5.77 AU from the star.[1]

A limitation of the radial velocity method used to discover 55 Cancri d is that only a lower limit on the planet's mass can be obtained. In the case of 55 Cancri d, this lower limit was around 3.835 times the mass of Jupiter. In 2004, astrometric measurements with the Fine Guidance Sensors on the Hubble Space Telescope suggest that the planet's orbit is inclined by around 53° with respect to the plane of the sky.[7] If this measurement is confirmed, it implies that the planet's true mass is 25% greater than the lower limit, at around 4.8 Jupiter masses; and it will not be coplanar with the innermost planets e and b (both 85°).


Given the planet's high mass, the planet is a gas giant with no solid surface. Since the planet has only been detected indirectly, parameters such as its radius, composition, and temperature are unknown.

Assuming a composition similar to that of Jupiter and that the planet's atmosphere is close to chemical equilibrium, it is predicted that 55 Cancri d is covered in a layer of water clouds: the planet's internal heat probably keeps it too warm to form the ammonia-based clouds that are typical of Jupiter. Its surface gravity is likely to be about 4 to 5 times stronger than Jupiter, or about 10 to 15 times that of Earth which is because the radius of the planet is unlikely to be much more than Jupiter's and is probably slightly smaller than Jupiter due to the high metal content in the parent star.[8]

See also


  1. ^ a b c d e f g h DA Fischer; et al. (March 2008). "Five Planets Orbiting 55 Cancri". Astrophysical Journal 675 (1): 790–801.  
  2. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  3. ^ NameExoWorlds.
  4. ^ NameExoWorlds.
  5. ^ Butler; et al. (1997). "Three New 51 Pegasi-Type Planets". The  
  6. ^ a b Marcy, G.; et al. (2002). "A planet at 5 AU Around 55 Cancri".  
  7. ^ a b McArthur, B.; et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope".  
  8. ^ Sudarsky, D.; et al. (2003). "Theoretical Spectra and Atmospheres of Extrasolar Giant Planets".  

External links

  • Jean Schneider (2011). "Notes for Planet 55 Cnc d".  

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