Astronomers with the Wide Area Search for Planets have discovered a planet, dubbed WASP-17, that is twice the size of Jupiter. That makes it the largest planet ever discovered. Unlike any other planet discovered so far, it orbits opposite to its star's direction of rotation. Astronomer David Anderson from Keele University:
"Newly formed solar systems can be violent places. Our own Moon is thought to have been created when a Mars-sized planet collided with the recently formed Earth and threw up a cloud of debris. A near collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit."
But why is WASP-17 so big? The discovery team suggests that have been subjected to intense tides as it travelled in its strange and highly-elliptical orbit, causing it to become stretched and bloated.