HD 17156 c

HD 17156 c is a plausible extrasolar planet approximately 255 light-years away in the constellation of Cassiopeia. The planet is thought to be orbiting the yellow giant star HD 17156. This planet has a mass of 0.063 Jupiter mass (or 20 Earth masses) and takes about 111.314 days or 0.305 year to orbit the star, classifying the planet as a cool Neptunian planet. This put it in the distance of 0.481 astronomical units or 72.0 gigameters with a moderate eccentricity.

The two planets "exchange angular momentum in a 5:1 mean motion resonance".

This planet was discovered on the vernal equinox of 2008 by analyzing perturbations with the inner planet HD 17156 b. The paper was submitted to Astrophysical Journal Letters 20 March and revised 14 June.