WASP-17b

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 challenged traditional planetary formation theory. In terms of diameter, WASP-17b is the second-largest exoplanet discovered yet, and at half Jupiter's mass, this makes it the most puffy planet known. On 3 December 2013, scientists working with the Hubble Space Telescope reported detecting water in the atmosphere of the exoplanet.

Discovery

A team of researchers led by David Anderson of Keele University in Staffordshire, England, discovered the gas giant, which is about 1,000 light years (300 parsecs) from Earth, by observing it in transit its host star WASP-17. Such photometric observations also reveal the planet's size. The discovery was made with a telescope array at the South African Astronomical Observatory. Due to the involvement of the Wide Angle Search for Planets SuperWASP consortium of universities, the exoplanet, as the 17th found to date by this group, was given its present name.