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WASP-42 b

The only known planet of WASP-42, a small orange star in the constellation of Centaurus. The system lies some 522 light years from the Sun, though with some considerable uncertainty over its precise distance. WASP-42 is a dwarf star, comparatively rather cooler than the Sun and about ninety percent of its diameter.

The planet WASP-42 b is physically a gas giant, marginally larger than Jupiter, though considerably less dense. It orbits extremely close to its parent star, at a distance of just 0.05 AU (that is, about eight times closer to WASP-42 than Mercury is to the Sun). This means that surface temperatures on the planet are extreme, estimated at about 1,000 K. Due to its proximity to the star, the orbit of WASP-42 b is very rapid, with the planet completing one circuit of the star in just under five days.

A further curious element of the orbit of WASP-42 b is that it is very nearly polar. While most planets follow an orbital path aligned with their star's plane of rotation, WASP-42 b is inclined by 88°, meaning that its orbit carries it almost exactly over the poles of WASP-42. This is not a unique situation, but orbits like this are extremely rare. The implications are unclear, but the planet certainly cannot have originated in this peculiar configuration. This may point to violent events in the system's past, or perhaps even hint that WASP-42 b was originally a rogue planet, captured by the gravitational pull of the star WASP-42.