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55 Cancri f

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55 Cancri f
Exoplanet List of exoplanets
Artist's concept shows four of the five planets that orbit 55 Cancri, a star much like our own.jpg
An artist's impression of 55 Cancri f.
The three bright dots near its star are the three innermost planets.
Parent star
Star 55 Cancri A
Constellation Cancer
Right ascension (α) 08h 52m 35.8113s[1]
Declination (δ) +28° 19′ 50.957″[1]
Apparent magnitude (mV) 5.95
Distance41.06±0.04[1] ly
(12.59±0.01[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) 0.781 ± 0.007[2] AU
Periastron (q) 0.730 AU
Apastron (Q) 0.833 AU
Eccentricity (e) 0.2 ± 0.2[2]
Orbital period(P) 260.00 ± 1.1[2] d
(0.7118 y)
Argument of
(ω) 181.1 ± 60[2]°
Time of periastron (T0) 2,450,080.9108 ± 1.1[2] JD
Semi-amplitude (K) 4.879 ± 0.6[2] m/s
Physical characteristics
Minimum mass(m sin i)0.144 ± 0.04[2] MJ
(45.7 ± 12.7[2] M)
Stellar flux(F)~1
Temperature (T) 200–300 K (−73–27 °C; −100–80 °F)
Discovery information
Discovery date 11 April 2005 (announced)
6 November 2007 (published)
Discoverer(s) announced by J. Wisdom
published by D. Fischer
Discovery method Doppler spectroscopy
Discovery site  United States
Discovery status Published
Other designations
Harriot, 55 Cancri Af, Rho1 Cancri f, HD 75732 f
Database references
Extrasolar Planets
Exoplanet Archivedata
Open Exoplanet Cataloguedata

55 Cancri f (abbreviated 55 Cnc f), also designated Rho1 Cancri f and named Harriot, 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".[3]

In July 2014 the International Astronomical Union launched a process for giving proper names to certain exoplanets and their host stars.[4] The process involved public nomination and voting for the new names.[5] In December 2015, the IAU announced the winning name was Harriot for this planet.[6] The winning name was submitted by the Royal Netherlands Association for Meteorology and Astronomy of the Netherlands. It honors the astronomer Thomas Harriot.[7]


Radial velocity changes over time of 55 Cancri caused by the orbit of 55 Cancri f.

The initial presentation of this planet occurred at a meeting of the American Astronomical Society in April 2005,[8] however it was another two and a half years before the planet was to be published in a peer-reviewed journal.[2] It is the first known planet outside our solar system to spend its entire orbit within what astronomers call the "habitable zone".[9] Furthermore, its discovery made 55 Cancri the first star other than the Sun known to have at least five planets.

Orbit and mass[edit]

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 262 days to complete a full orbit.[10] 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.[10] 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-squared statistic of the fit, thus a representative eccentricity of 0.2±0.2 was assumed.[2] In a Newtonian model which takes interactions between the planets into account, the eccentricity comes out as 0.0002, almost perfectly circular.[2]

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.[11] The inner planets b and e are inclined at 85°. The inclination of f is unknown.


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,[10] 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.[9]

It is not known if the composition and appearance is more like that of Saturn or Neptune.[3] Based on its temperature, it should be a Sudarsky Class II planet, covered in water clouds.[citation needed]


  1. ^ a b c d Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia Data Release 2 Vizier catalog entry
  2. ^ a b c d e f g h i j k Debra A. Fischer; Geoffrey W. Marcy; R. Paul Butler; Steven S. Vogt; Greg Laughlin; Gregory W. Henry; et al. (23 December 2007). "Five Planets Orbiting 55 Cancri". Astrophysical Journal. 675: 790–801. arXiv:0712.3917. Bibcode:2008ApJ...675..790F. doi:10.1086/525512.
  3. ^ a b Shige Abe (12 November 2007). "Researchers Identify First Five-Planet Extrasolar System". NASA Astrobiology. Archived from the original on 16 September 2008. Retrieved 17 September 2008.
  4. ^ NameExoWorlds: An IAU Worldwide Contest to Name Exoplanets and their Host Stars. 9 July 2014
  5. ^ NameExoWorlds The Process
  6. ^ Final Results of NameExoWorlds Public Vote Released, International Astronomical Union, 15 December 2015.
  7. ^ NameExoWorlds The Approved Names
  8. ^ J. Wisdom (11 April 2005). "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 16 December 2006. Retrieved 17 September 2008.
  9. ^ a b Ian Sample, science correspondent (7 November 2007). "Could this be Earth's near twin? Introducing planet 55 Cancri f". London: The Guardian. Archived from the original on 2 October 2008. Retrieved 17 October 2008.
  10. ^ a b c Jean Schneider (2011). "Notes for Planet 55 Cnc f". Extrasolar Planets Encyclopaedia. Retrieved 8 October 2011.
  11. ^ Han; et al. (2001). "Preliminary Astrometric Masses for Proposed Extrasolar Planetary Companions". The Astrophysical Journal Letters. 548 (1): L57–L60. Bibcode:2001ApJ...548L..57H. doi:10.1086/318927.

External links[edit]

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