Tags: Planet.
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.
