The planet WASP-21b is 1.21 times the radius of Jupiter, the largest planet in our Solar System. It is vastly bigger than Earth.
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.
WASP-21b was the first exoplanet found to be transiting a star in the galaxy’s “thick disk”. Our galaxy has spiral arms surrounding a central bulge. It thus looks like this (plan view of the left, edge-on view on the right), with our Sun being out in one of the spiral arms:
But the flattened disk is itself composed of a thicker disk and a thinner disk. Most stars we see are in the “thin” disk, which contains a lot of gas and dust and regions of star formation giving birth to new stars. The “thick” disk contains little gas and dust and is composed of older stars born billions of years ago.
For more information visit http://exoplanet.eu/catalog/wasp-21_b/.