HD 17156 and Its Jupiter-Like Planet

HD 17156 is a G0 V star 255 light-years away. That spectral type marks it as a main-sequence dwarf of the same temperature class as the Sun. It is 5.7 billion years old, with a mass of 1.2 solar masses larger than the Sun's and a radius of 1.47 solar radii also larger than the Sun's. Its temperature of 6080 K is hotter than the Sun's. One planet orbits this host.

HD 17156 b is a Jupiter-like planet found in 2007 by the radial velocity method, which measures the wobble a planet's gravity induces in its star's motion. It has a mass of 1040 Earth masses, roughly 3.26 times Jupiter's mass, and a radius of 12.3 Earth radii. Both its mass and radius estimates are larger than Earth's. Its orbital period is 21.2 days. Its mean density is 3.1 g/cm³, 0.562 times Earth's.