55 Cancri d

55 Cancri d
Extrasolar planet List of extrasolar planets

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
Semimajor 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
periastron		 (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
Discovery information
Discovery date June 13, 2002
Discoverer(s) Marcy et al.
Detection 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
Encyclopaedia		 data
SIMBAD 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.

Contents

Discovery

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.[2]

In 2002, further measurements revealed the presence of a long-period planet in an orbit at around 5 AU from the star.[3] The same measurements also indicated the presence of another inner planet, designated 55 Cancri c.

Orbit and mass

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.[3] 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).[4] 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.[4] 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.

Characteristics

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 times stronger than Jupiter, or about 10 times that of Earth which is because the radius of the planet is unlikely to be much more than Jupiter's.[5]

See also

Book: 55 Cancri
Wikipedia books are collections of articles that can be downloaded or ordered in print.


References

  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. Bibcode 2008ApJ...675..790F. doi:10.1086/525512. 
  2. ^ Butler et al. (1997). "Three New 51 Pegasi-Type Planets". The Astrophysical Journal 474 (2): L115–L118. Bibcode 1997ApJ...474L.115B. doi:10.1086/310444. 
  3. ^ a b Marcy, G. et al. (2002). "A planet at 5 AU Around 55 Cancri". The Astrophysical Journal 581 (2): 1375–1388. arXiv:astro-ph/0207294. Bibcode 2002ApJ...581.1375M. doi:10.1086/344298. 
  4. ^ a b McArthur, B. et al. (2004). "Detection of a NEPTUNE-mass planet in the ρ1 Cnc system using the Hobby-Eberly Telescope". The Astrophysical Journal 614 (1): L81 – L84. arXiv:astro-ph/0408585. Bibcode 2004ApJ...614L..81M. doi:10.1086/425561. 
  5. ^ 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. 

External links

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