HD 217107 c

2007 Schools Wikipedia Selection. Related subjects: Space (Astronomy)

HD 217107 c
Extrasolar planet Lists of extrasolar planets
Orbital elements
Semimajor axis (a) 4.3 ± 2 AU
Eccentricity (e) 0.55 ± 0.20
Orbital period (P) 3150 ± 1000 d (8.6 y)
Inclination (i) °
Longitude of
(ω) 164 ± 30.2°
Time of periastron (τ) 2,451,030 ± 300 JD
Physical characteristics
Mass (m) >2.1 ± 1 MJ
Radius (r)  ? RJ
Density (ρ)  ? kg/ m3
Temperature (T)  ? K
Discovery information
Discovery date 1999-2005
Discoverer(s) Marcy et al.
Detection method Doppler Spectroscopy
Discovery status Confirmed

HD 217107 c is a Jupiter-like extrasolar planet orbiting the star HD 217107 about every eight years. It is the second planet to be discovered orbiting the star, after HD 217107 b which orbits the star in a much smaller orbit. HD 217107 c's existence was hypothesised in 2002 and confirmed in 2005, when radial velocity studies of the star indicated another, more distant and massive companion orbiting the star. Its mass and orbital parameters remain highly uncertain.


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, indicating the presence of a planet in orbit around the star. The planet was designated HD 217107 b, and was found to be somewhat heavier than Jupiter, and orbiting extremely close to the parent star in an orbit with quite a large eccentricity .

Most planets with orbital periods of less than 10 days have almost circular orbits, and its discoverers proposed that the high eccentricity of HD 217107 b's orbit could be due to the gravitational influence of a second planet in the system at a distance of several astronomical units (AU). Confirmation of the existence of the second planet followed in 2005, and it was designated HD 217107 c.


Observations of the star's radial velocity variations indicate a period of about 8 years, and HD 217107 c's mass is thought to be at least twice that of Jupiter in a very eccentric orbit with a semimajor axis of about 4 AU . Large uncertainties still exist in these measurements, though, due to the length of the orbital period and the distance of HD 217107 c from its parent star.

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