High Quality Content by WIKIPEDIA articles! WASP-17b is an exoplanet in the constellation Scorpius that is orbiting the star WASP-17. Its discovery was announced on 11 August 2009. It is the first planet discovered to have a retrograde orbit, meaning it orbits in a direction counter to the rotation of its host star. This discovery changed traditional planetary theory. In terms of diameter, WASP-17b may be the largest exoplanet discovered yet, and at half Jupiter`s mass, this would make it the most diffuse known planet, and a puffy planet.