New planet displays ‘retrograde’ orbit

An international team of astronomers has discovered the first planet that orbits in the opposite direction compared to the rotation of its host star.

Planets circle their host stars in the same direction stars rotate. The newly discovered planet, however, is an exception.

The planet, designated WASP-17, is twice the size of Jupiter, the fifth planet from the sun, yet it weighs only half of Jupiter due to a density like that of expanded polystyrene.

Such a motion, known as a “retrograde orbit,” is odd since both star and planet are expected to travel in the common West to East orbit.

The common direction is the result of the same material from which both planets and their stars are created. Planets form out of the same swirling gas cloud that creates a star.