HD 217107 b

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

HD 217107 b
Extrasolar planet Lists of extrasolar planets
Orbital elements
Semimajor axis (a) 0.074 ± 0.002 AU
Eccentricity (e) 0.13 ± 0.02
Orbital period (P) 7.1269 ± 0.00022 d
Inclination (i)  ?°
Longitude of
(ω) 21.1°
Time of periastron (τ) 2,449,998.4241 ± 0.17 JD
Physical characteristics
Mass (m) >1.37 ± 0.14 MJ
Radius (r)  ? RJ
Density (ρ)  ? kg/ m3
Temperature (T)  ? K
Discovery information
Discovery date 1998
Discoverer(s) Marcy et al.
Detection method Doppler Spectroscopy
Discovery status Confirmed

HD 217107 b is an extrasolar planet orbiting the Sun-like star HD 217107 every 7.1 days. It is the innermost known planet in its system, and was discovered by the California and Carnegie Planet Search team. It is a ' hot Jupiter' planet, so-called because of its high mass and proximity to its parent star.


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 . The planet's mean distance from the star is less than one fifth of Mercury's distance from the Sun.

Indication of second planet

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 hypothesised that this 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 a second planet, HD 217107 c, followed in 2005

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