Alien World Has 8-Hour Day

ESO L. Calçada/N. Risinger (

ScienceShot: Alien World Has 8-Hour Day

For the first time, researchers have measured how quickly a planet in a distant solar system rotates—and boy, is it fast. The object, dubbed β Pictoris b, is a gas giant that the researchers estimate is about 11 times the mass of Jupiter, and it orbits a young, hot star in Pictor, a minor constellation best seen from the Southern Hemisphere. Analyses of near-infrared light from the exoplanet (depicted in an artist’s representation) reveal that the rotational speed at its equator is about 25 kilometers per second—faster than that of any planet in our solar system, the researchers report online today in Nature. When combined with data from previous studies, which suggest that the planet’s diameter is about 65% larger than Jupiter’s, that suggests that the planet rotates once every 8 hours or so. That’s slightly longer than expected for a planet of its mass but may be unusually high simply because the planet hasn’t yet cooled and shrunk to its final size, the researchers say. In the distant future, when β Pictoris b is about the size of Jupiter, its day will be about 4 hours long, the researchers estimate.

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