HD 156668 b

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HD 156668 b
Exoplanet List of exoplanets
Parent star
Star HD 156668
Constellation Hercules
Right ascension (α) 17h 17m 40s
Declination (δ) +29° 13′ 38″
Apparent magnitude (mV) 8.42
Distance 78.5 ± 2.0 ly
(24.1 ± 0.6 pc)
Spectral type K2V
Physical characteristics
Minimum mass (m sin i) 3.1 ± 0.4[1] M
Orbital elements
Semi-major axis (a) 0.04998 ± 0.00083[2] AU
Eccentricity (e) 0.000[1]
Orbital period (P) 4.6455 ± 0.0011[2] d
Argument of
(ω) 0[1]°
Time of conjunction (Tc) 2454718.57 ± 0.11[2] JD
Semi-amplitude (K) 1.89 ± 0.26 [2] m/s
Discovery information
Discovery date 2010-01-06
Discoverer(s) Howard et al.
Discovery method Doppler Spectroscopy
Discovery site Keck Observatory
Discovery status Submitted
Database references
Extrasolar Planets
Exoplanet Archive data
Open Exoplanet Catalogue data

HD 156668 b is an extrasolar planet orbiting the star HD 156668 78.5 light-years away in the constellation Hercules. It has a minimum mass of 3.1 Earth masses. At the time of discovery it was the second least massive planet discovered by the radial velocity method, subject to the mass/inclination degeneracy that affects radial velocity measurements.[3] The only radial velocity planet less massive than this planet is Gliese 581 e, which was discovered on April 21, 2009, and has a minimum mass of 1.94 Earth masses. In addition to this, it has the lowest semi-amplitude, or the speed of the stellar wobble caused by planet's gravity tugging on the star determined by radial velocity, at 2.2 m/s.[3] This planet was discovered on January 6, 2010; it is the 8th planet discovered in 2010 after the first five planets detected by Kepler on January 4 and two planets around HD 9446 on January 5.


  1. ^ a b c Dawson, Rebekah I.; Fabrycky, Daniel C. (2010). "Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e". The Astrophysical Journal. 722 (1): 937–953. Bibcode:2010ApJ...722..937D. arXiv:1005.4050Freely accessible. doi:10.1088/0004-637X/722/1/937. 
  2. ^ a b c d Andrew W. Howard; John Asher Johnson; Geoffrey W. Marcy; Debra A. Fischer; Jason T. Wright; Gregory W. Henry; Howard Isaacson; Jeff A. Valenti; Jay Anderson; Nikolai E. Piskunov (2010). "The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses". arXiv:1003.3444v1Freely accessible [astro-ph.EP]. 
  3. ^ a b "Second Smallest Exoplanet Found To Date At Keck". W.M. Keck Observatory. 2010-01-07. Retrieved 2010-01-07.