By default, planets will orbit around their central star in the same direction. However, one planet discovered by a team of researchers, dubbed WASP-17b, is going against the status quo.

But gravitational interference might be a bit of a stretch here: the planet's orbit is 150 degrees opposed, or almost directly opposite, the star's rotation. It'd take a pretty significant gravitational shove to get this much of a difference.

WASP-17b is notable for a couple of other reasons, too, all described in a paper submitted to the Astrophysical Journal. WASP-17b is possibly the largest yet discovered exo-planet, at twice the width of Jupiter. It's also pretty light, at only half of Jupiter's mass. That leaves the planet with a consistency similar to polystyrene, a light, puffed up ball of mostly nothing.The research team thinks this might be an effect of its very close (7 million kilometers), very quick (only 3.7 days) orbit yanking materials around inside the body and deforming it into this weird puffy planet.

This is a strange phenomenon. But yet it reminds us that there's so much more of the universe that we don't know just yet.

Planet found orbiting its star backwards for first time [via NewScientist]
Paper: WASP-17b: an ultra-low density planet in a probable retrograde orbit [arXiv.org]

(Illustration: what such a close-orbiting planet may look like, from ESA/C. Carreau)