51 Pegasi b

The exoplanet 51 Pegasi b orbits a yellow dwarf star, 50 lightyears from the Solar system. Its mass is 46 percent that of our Planet Jupiter, while its orbit is only 4.6 days, taking it very close to its primary. That makes its atmosphere very hot, so that it is much less dense than Jupiter, with a diameter much greater thn Jupiter's. It has been classed as a hot Jupiter and a puffball planet.