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XO-3b [1]
Exoplanet List of exoplanets
Exoplanet Comparison XO-3 b.png
Size comparison of XO-3b with Jupiter.
Parent star
Star XO-3
Constellation Camelopardalis[2]
Right ascension (α) 04h 21m 52.709s[3]
Declination (δ) +57° 49′ 01.87″[3]
Distance 568 ± 59[4] ly
(174 ± 18[4] pc)
Spectral type F5V[1]
Orbital elements
Semi-major axis (a) 0.0454 ± 0.00082[4] AU
Eccentricity (e) 0.2883 ± 0.0025[5]
Orbital period (P) 3.1915289 ± 0.0000032[6] d
Inclination (i) 84.20 ± 0.54[4]°
Argument of
(ω) 346.1+1.2
Time of transit (Tt) 2454449.86816 ± 0.00023[4] JD
Semi-amplitude (K) 1494.0 ± 9.5[5] m/s
Physical characteristics
Mass (m) 11.79 ± 0.59[4] MJ
Radius (r) 1.217 ± 0.073[4] RJ
Discovery information
Discovery date May 30, 2007
Discoverer(s) XO Project[1]
Discovery method Transit,
Radial velocity[1]
Other detection methods Orbital light variations
Discovery site XO telescope Maui, Hawaii[1]
Discovery status Published[1]

XO-3b is an exoplanet with about 11.79 times the mass of Jupiter, and an orbit around its parent star in about 3.2 days.[7] The radius of this object is 1.217 times that of Jupiter. Astronomers announced their discovery on May 30, 2007, at the American Astronomical Society in Honolulu, Hawaii. Its discovery is attributed to the combined effort of amateur and professional astronomers working together on the XO Project using a telescope located on the Haleakala summit in Hawaii.[8]

Dubbed an "oddball" planet, the planet stands out from over 350 other extrasolar planets as the most massive planet found in close proximity to a star, yet the orbit is significantly elliptical instead of circular, as would be expected.[8] It is also considered a transiting planet, passing in front of its parent star during each orbit. It is the third such planet to be found by the XO Project which was specifically created to locate them.[9]

Orbital inclination[edit]

Measurements of the Rossiter–McLaughlin effect allow a determination of the angle between the planet's orbital plane and the equator of the parent star. Initial reports suggested this angle was very large, at 70 ± 15 degrees,[10] which is significantly larger than that of the other transiting planets for which this measurement has been made.[11] The authors cautioned that systematic effects may have affected the measurements, and a later determination by an independent group of astronomers determined a reduced value of 37.3 ± 3.7 degrees. This value is however still larger than the misalignment between the Sun's equator and the orbital plane of Jupiter, which is only 6°.[6]

The misalignment may indicate that in the past an encounter with another planet altered its orbit, kicking it out of the plane of the planetary system.[12] Another planetary system that may have also undergone such planet-planet interactions is Upsilon Andromedae.[13]


There is currently a debate over the classification of this object as either a planet or a brown dwarf. One of the leading astronomers in this discussion is Christopher Johns-Krull, who indicated that the debate is still quite lively. This is not particularly unusual or strange, as it would not be the first of many brown dwarfs orbiting mother stars.[7]

The light curve that better match the steepness of ingress and egress implies a planetary radius of 1.32 ± 0.15 RJ and a mass of 11.71 ± 0.46 MJ.[1]

See also[edit]


  1. ^ a b c d e f g Johns-Krull, Christopher M.; et al. (2008). "XO-3b: A Massive Planet in an Eccentric Orbit Transiting an F5V Star". The Astrophysical Journal. 677 (1): 657–670. arXiv:0712.4283Freely accessible. Bibcode:2008ApJ...677..657J. doi:10.1086/528950. 
  2. ^ Roman, Nancy G. (1987). "Identification of a Constellation From a Position". Publications of the Astronomical Society of the Pacific. 99 (617): 695–699. Bibcode:1987PASP...99..695R. doi:10.1086/132034.  Vizier query form
  3. ^ a b Hog; et al. (2000). "TYC 3727-1064-1". The Tycho-2 Catalogue. Retrieved 2012-01-16. 
  4. ^ a b c d e f g Winn, Joshua N.; et al. (2008). "The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b". The Astrophysical Journal. 683 (2): 1076–1084. arXiv:0804.4475Freely accessible. Bibcode:2008ApJ...683.1076W. doi:10.1086/589737. 
  5. ^ a b c Hirano, Teruyuki; et al. (2011). "Further Observations of the Tilted Planet XO-3: A New Determination of Spin-Orbit Misalignment, and Limits on Differential Rotation". Publications of the Astronomical Society of Japan. 63 (6): L57–L61. arXiv:1108.4493Freely accessible. Bibcode:2011PASJ...63L..57H. doi:10.1093/pasj/63.6.l57. 
  6. ^ a b Winn, Joshua N.; et al. (2009). "On the Spin-Orbit Misalignment of the XO-3 Exoplanetary System". The Astrophysical Journal. 700 (1): 302–308. arXiv:0902.3461Freely accessible. Bibcode:2009ApJ...700..302W. doi:10.1088/0004-637X/700/1/302. 
  7. ^ a b Oddball Planet Puzzles Astronomers, Space.com
  8. ^ a b Space oddity: Astronomers discover giant planet, The Times of India
  9. ^ XO-3 b: Supersized planet or oasis in the 'brown dwarf desert'?, EurekAlert!
  10. ^ Hébrard, G.; et al. (2008). "Misaligned spin-orbit in the XO-3 planetary system?". Astronomy and Astrophysics. 488 (2): 763–770. arXiv:0806.0719Freely accessible. Bibcode:2008A&A...488..763H. doi:10.1051/0004-6361:200810056. (web preprint)
  11. ^ Joshua N. Winn (2008). "Measuring accurate transit parameters". Proceedings of the International Astronomical Union. 4: 99. arXiv:0807.4929v2Freely accessible. doi:10.1017/S174392130802629X. 
  12. ^ Powell, Devin (2008-09-22). "Planet's strange orbit points to planetary billiards". New Scientist. Retrieved 2008-09-23. 
  13. ^ Ford, E.; et al. (2005). "Planet-planet scattering in the upsilon Andromedae system". Nature. 434 (7035): 873–876. arXiv:astro-ph/0502441Freely accessible. Bibcode:2005Natur.434..873F. doi:10.1038/nature03427. PMID 15829958. 

External links[edit]

Media related to XO-3b at Wikimedia Commons

Coordinates: Sky map 04h 21m 53s, +57° 49′ 01″