HAT-P-4b

HAT-P-4b is an extrasolar planet orbiting the star HAT-P-4 over 1000 light years away in Boötes constellation. It was discovered by transit on October 2, 2007, which looks for slight dimming of stars caused by planets that passed in front of them. It is the fourth planet discovered by the HATNet Project.

It is a hot Jupiter with 68% the mass and 127% the radius of Jupiter, and 41% the density of water (31% of Jupiter). Since the inclination is known by transit observation, the true mass is known.