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55 Cancri f
Extrasolar planet List of extrasolar planets
196222main exoplanet-final.jpg
An artist's impression of 55 Cancri f.
The stars around its sun are the three innermost 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 40.9 ly
(12.5 pc)
Spectral type G8V
Orbital elements
Semimajor axis (a) 0.781 ± 0.007[1] AU
(116.9 Gm)
    62.5 mas
Periastron (q) 0.730 AU
(109.1 Gm)
Apastron (Q) 0.833 AU
(124.6 Gm)
Eccentricity (e) 0.2 ± 0.2[1]
Orbital period (P) 260.00 ± 1.1[1] d
(0.7118 y)
Argument of
(ω) 181.1 ± 60[1]°
Time of periastron (T0) 2,450,080.9108 ± 1.1[1] JD
Semi-amplitude (K) 4.879 ± 0.6[1] m/s
Physical characteristics
Minimum mass (m sin i) 0.144 ± 0.04[1] MJ
(45.7 ± 12.7[1] M)
Discovery information
Discovery date 11 April 2005 (announced)
6 November 2007 (published)
Discoverer(s) announced by J. Wisdom
published by D. Fischer
Detection method Doppler spectroscopy
Discovery site  United States
Discovery status Published
Other designations
55 Cancri Af, Rho1 Cancri f, HD 75732 f
Database references
Extrasolar Planets

55 Cancri f, also referred to as Rho1 Cancri f, is an extrasolar planet approximately 41 light-years away from Earth in the constellation of Cancer (the Crab). 55 Cancri f is the fourth known planet (in order of distance) from the star 55 Cancri and the first planet to have been given the designation of "f".[2] As of July 2009, this makes 55 Cancri the only planetary system outside the Solar System that is known to contain at least five planets.



The initial presentation of this planet occurred at a meeting of the American Astronomical Society in April 2005,[3] however it was another two and a half years before the planet was to be published in a peer-reviewed journal.[1] It is the first known planet outside our solar system to spend its entire orbit within what astronomers call the "habitable zone".[4] Furthermore, its discovery made 55 Cancri the first star other than the Sun known to have five planets. As of September 2008, this is still the only planetary system outside the Solar System that is known to contain at least five planets.[5]

Orbit and mass

55 Cnc f's orbit compared to the orbit of Venus (0.72AU).

55 Cancri f is located about 0.781 AU away from the star and takes 260 days to complete a full orbit.[6] A limitation of the radial velocity method used to detect 55 Cancri f is that only a minimum mass can be obtained, in this case around 0.144 times that of Jupiter, or half the mass of Saturn.[6] A Keplerian fit to the radial velocity data of 55 Cancri A indicates that the orbit is consistent with being circular, however changing the value in a range between 0 and 0.4 does not significantly alter the chi-square statistic of the fit, thus a representative eccentricity of 0.2±0.2 was assumed.[1] In a Newtonian model which takes interactions between the planets into account, the eccentricity comes out as 0.0002, almost circular.[1]

Astrometric observations made with the Hubble Space Telescope suggest that the outer planet 55 Cancri d is inclined at 53° with respect to the plane of the sky.[7] If these measurements are confirmed and the system is assumed to be coplanar, the true mass of 55 Cancri f would therefore be about 25% greater than this lower limit, at around 0.18 Jupiter masses.[1]


Since the planet was detected indirectly through observations of its star, properties such as its radius, composition and temperature are unknown. With a mass half that of Saturn,[6] 55 Cancri f is likely to be a gas giant with no solid surface. It orbits in the so-called "habitable zone," which means that liquid water could exist on the surface of a possible moon.[8]

We do not know if the composition and appearance is more like Saturn or Neptune.[2] Based on its temperature, it should be a Sudarsky Class II planet, covered in water clouds.

See also


  1. ^ a b c d e f g h i j k l Debra A. Fischer, Geoffrey W. Marcy, R. Paul Butler, Steven S. Vogt, Greg Laughlin, Gregory W. Henry, David Abouav, Kathryn M. G. Peek, Jason T. Wright, John A. Johnson, Chris McCarthy, Howard Isaacson (2007-12-23). "Five Planets Orbiting 55 Cancri". Astrophysics. Retrieved 2008-09-17.  
  2. ^ a b Shige Abe (2007-11-12). "Researchers Identify First Five-Planet Extrasolar System". NASA Astrobiology. Retrieved 2008-09-17.  
  3. ^ J. Wisdom (2005-04-11). "A Neptune-sized Planet in the rho1 Cancri System". DDA 36th Meeting, 10-14 April 2005—Session 5 Posters (The American Astronomical Society). Archived from the original on 2006-12-16. Retrieved 2008-09-17.  
  4. ^ Ian Sample, science correspondent. "Could this be Earth's near twin? Introducing planet 55 Cancri f". The Guardian. Retrieved 2008-10-17.  
  5. ^ "The Extrasolar Planets Encyclopaedia". Retrieved 2008-09-14.  
  6. ^ a b c "Notes for Planet 55 Cnc f". The Extrasolar Planets Encyclopaedia. Retrieved 2008-09-14.  
  7. ^ Han et al.; Black, David C.; Gatewood, George (2001). "Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions". The Astrophysical Journal Letters 548 (1): L57–L60. doi:10.1086/318927.  
  8. ^ Sample, Ian (2007-11-07). "Could this be Earth's near twin? Introducing planet 55 Cancri f". The Guardian. Retrieved 2008-09-17.  

External links

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



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