The planet WASP-21b is 1.21 times the radius of Jupiter, the largest planet in our Solar System.
WASP-21b is about the same mass as Saturn. That’s about a third the mass of Jupiter, which means that WASP-21b is much less dense.
WASP-21b orbits at a distance of 7.77 million km, taking 4.32 days to go round its orbit.
From Earth, WASP-21 lies in the constellation of Pegasus. In terms of coordinates, it has a right ascension of 23:09:58.0 and a declination of +18:23:46. The system is a distance of 230 parsecs from us.
The planet was discovered in 2010. It is one of the least dense planets discovered by ground-based transit searches to date and has roughly the mass of Saturn. It also seems to be the first transiting planet belonging to the thick disk.
For more information visit http://exoplanet.eu/catalog/wasp-21_b/.