HD 217107 b

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HD 217107 b
Extrasolar planet List of extrasolar planets
Parent star
Star HD 217107
Constellation Pisces
Right ascension (α) 22h 58m 15.54s
Declination (δ) −2° 23′ 43.39″
Distance 64.3 ± 1 ly
(19.7 ± 0.3 pc)
Spectral type G8IV
Orbital elements
Semimajor axis (a) 0.074 ± 0.002 AU
Eccentricity (e) 0.13 ± 0.02
Orbital period (P) 7.1269 ± 0.00022 d
Argument of
periastron
(ω) 21.1°
Time of periastron (T0) 2,449,998.4241 ± 0.17 JD
Semi-amplitude (K) 140.7 ± 2.6 m/s
Physical characteristics
Mass (m) >1.37 ± 0.14 MJ
Discovery information
Discovery date November 24, 1998
Discoverer(s) Marcy et al.
Discovery method Doppler spectroscopy
Discovery site United States
Discovery status Confirmed

HD 217107 b is an extrasolar planet[1] approximately 64 light-years away from Earth in the constellation of Pisces (the Fish). The planet was discovered orbiting the star HD 217107 approximately every seven days, classifying the planet as a hot Jupiter. Because of the planet's somewhat eccentric orbit, scientists were able to confirm another planet within the system (HD 217107 c).

Discovery[edit]

As with the majority of extrasolar planet discoveries so far, it was found by detecting small variations in the radial velocity of the star it orbits, caused by the tug of its gravity. A study of the radial velocity of HD 217107 carried out in 1998 revealed that its motion along the line of sight varied over a 7.1 day cycle. The period and amplitude of this variation indicated that it was caused by a planetary companion in orbit around the star, with a minimum mass slightly greater than that of Jupiter.[2] The planet's mean distance from the star is less than one fifth of Mercury's distance from the Sun.

Indication of second planet[edit]

While most planets with orbital periods of less than 10 days have almost circular orbits, HD 217107 b has a somewhat eccentric orbit, and its discoverers hypothesized that this could be due to the gravitational influence of a second planet in the system at a distance of several astronomical units (AU).[3] Confirmation of the existence of a second planet, HD 217107 c, followed in 2005.

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Coordinates: Sky map 22h 58m 15.54s, −02° 23′ 43.39″