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Exoplanet List of exoplanets
Exoplanet Comparison HAT-P-2 b.png
Size comparison of HAT-P-2b with Jupiter.
Parent star
Star HD 147506
Constellation Hercules[1]
Right ascension (α) 16h 20m 36.36s[2]
Declination (δ) +41° 02′ 53.1″[2]
Distance 370±30[2] ly
(114±10[2] pc)
Spectral type F8V[3]
Orbital elements
Semi-major axis (a) 0.0663±0.0039[4] AU
Eccentricity (e) 0.50910±0.00048[4]
Orbital period (P) 5.6334729±0.0000061 days[5] d
Inclination (i) 85.97+0.28
Argument of
(ω) 188.09±0.39[4]°
Time of periastron (T0) 2455289.4721±0.0038[4] JD
Semi-amplitude (K) 983.9±17.2[5] m/s
Physical characteristics
Mass (m) 8.00±0.97[4] MJ
Radius (r) 1.106±0.061[4] RJ
Density (ρ) 7300±1600[4] kg m−3
Surface gravity (g) 162±27[4] m/s²
Temperature (T) 1187[6]
Discovery information
Discovery date 2007-05-02
Discoverer(s) HATNet Project[3]
Discovery method Transit
Other detection methods Radial velocity,
Orbital phase reflected light variations
Discovery status Published[3]

HAT-P-2b is an extrasolar planet detected by the HATNet Project in May 2007. It orbits a class F star, (bigger and hotter than the Sun), located about 370 light-years away in the constellation Hercules. Every 5 days 15 hours, it crosses directly in front of the star as viewed from Earth.[3][7]

Orbit and mass[edit]

The planet's mass has been estimated to be 8.65 times that of Jupiter, while its diameter, at 135,978 km (84,493 mi), is 0.951 times Jupiter's. Its small size, despite the bloating of the planet's atmosphere, is caused by the strong gravity of the planet. This indicates its mean density is twice that of Earth and its surface gravity approximately 24 times that on Earth, almost equal to the Sun. The orbit is very eccentric, ranging from 4.90 million to 15.36 million miles from the star.[7]

In addition to heat from its primary star, tidal heating is thought to have played a significant role in this planet's evolution.[8]


As of August 2008, the most recent calculation of HAT-P-2b's Rossiter–McLaughlin effect and so spin-orbit angle was that of Winn in 2007 but Loeillet has in 2008 disputed it.[9][10] For Winn this is +1 ± 13 degrees.[11]

It has been suggested that there is a second outer planet perturbing HAT-P-2 b, although thus far, this has neither been proven or disproven.[7]


  1. ^ 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
  2. ^ a b c d van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752free to read. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  3. ^ a b c d Bakos, G. Á.; et al. (2007). "HD 147506b: A Supermassive Planet in an Eccentric Orbit Transiting a Bright Star". The Astrophysical Journal. 670 (1): 826–832. arXiv:0705.0126free to read. Bibcode:2007ApJ...670..826B. doi:10.1086/521866. 
  4. ^ a b c d e f g h i Lewis, Nikole K.; et al. (2013). "Orbital Phase Variations of the Eccentric Giant Planet HAT-P-2b". The Astrophysical Journal. 766 (2). 95. arXiv:1302.5084free to read. Bibcode:2013ApJ...766...95L. doi:10.1088/0004-637X/766/2/95. 
  5. ^ a b Pál, András; et al. (2010). "Refined stellar, orbital and planetary parameters of the eccentric HAT-P-2 planetary system". Monthly Notices of the Royal Astronomical Society. 401 (4): 2665–2674. arXiv:0908.1705free to read. Bibcode:2010MNRAS.401.2665P. doi:10.1111/j.1365-2966.2009.15849.x. 
  6. ^ Ravilious, Kate (May 3, 2007). ""Weird" New Planet Weighs as Much as 2,500 Earths". National Geographic News. Retrieved 2007-05-04. 
  7. ^ a b c "Astronomers find super-massive planet" (Press release). Harvard-Smithsonian Center for Astrophysics. May 2, 2007. 
  8. ^ Jackson, Brian; et al. (2008). "Tidal Heating of Extra-Solar Planets". ApJ. 681 (2): 1631. arXiv:0803.0026free to read. Bibcode:2008ApJ...681.1631J. doi:10.1086/587641. 
  9. ^ Joshua N. Winn (2008). "Measuring accurate transit parameters". Proceedings of the International Astronomical Union. 4: 99. arXiv:0807.4929v2free to read. doi:10.1017/S174392130802629X. 
  10. ^ Loeillet, B.; et al. (2008). "Refined parameters and spectroscopic transit of the super-massive planet HD 147506b". Astronomy and Astrophysics. 481 (2): 529–533. arXiv:0707.0679free to read. Bibcode:2008A&A...481..529L. doi:10.1051/0004-6361:20078167. 
  11. ^ Winn; et al. (2007). "Spin-Orbit Alignment for the Eccentric Exoplanet HD 147506b". Astrophysical Journal Letters. 665: L167. arXiv:0707.0503free to read. Bibcode:2007ApJ...665L.167W. doi:10.1086/521362. 

External links[edit]

Media related to HAT-P-2b at Wikimedia Commons

Coordinates: Sky map 16h 20m 36s, +41° 02′ 53″