The planet WASP-22b is 1.20 times the radius of Jupiter, the largest planet in our Solar System. It is thus much bigger than Earth.
WASP-22b is about double the mass of Saturn, which means that it is about one third the density of Jupiter.
WASP-22b orbits at a distance of 7.02 million km, taking 3.53 days to go round its orbit.
WASP-22b was announced in a paper led by Dr. Pierre Maxted of Keele University, one of the team operating WASP-South.
While WASP-22b is a large planet in a close-in orbit around its star, there must also be another planet (or possibly a low-mass star) in a much wider orbit. We know this because of a trend in the radial-velocity data. The radial-velocity shows us how the host star is pulled around by the gravity of the planet, but, after accounting for that motion, we also see a long-term trend (see plot below). This means there must be an unseen, massive planet in an orbit of hundreds of days or more.
Maybe the gravitational perturbations caused by the outer planet have pushed the inner planet, WASP-22b, into its current close-in orbit of only 3.5 days. This suggestion is called the Kozai effect. However, a paper led by Juliette Becker argues that the outer planet is in the same orbital plane as the inner planet, whereas in order to produce the Kozai effect it would have to be in a highly tilted orbit.
For more information visit http://exoplanet.eu/catalog/wasp-22_b/.