The planet WASP-39b is 1.3 times the radius of Jupiter, the largest planet in our Solar System. It is thus vastly bigger than our Earth.
Despite being much bigger, WASP-39b is only about a quarter the mass of Jupiter, which means that WASP-39b is much less dense. It is a huge, bloated planet, puffed up by extra heat inside it.
WASP-39b orbits at a distance of 7.27 million km, taking 4.06 days to go round its orbit.
NASA’s Hubble Space Telescope observed transits of WASP-39b in order to find out what the planet’s atmosphere is made of. It found that WASP-39b has clear skies, filled with water vapour but with few clouds.
WASP-39b was discovered by the SuperWASP-North array of cameras on top of an extinct volcano on the Island of La Palma. It was announced in 2011 in a paper led by Francesca Faedi.
For more information visit http://exoplanet.eu/catalog/wasp-39_b/.