The weather outlook on PSO J318.5-22 is cloudy and hot, with dust storms and the chance of showers—of molten iron. That forecast, according to a team of astronomers using the European Southern Observatory’s New Technology Telescope in Chile, is the first identification of weather on a planet outside our solar system. But PSO J318.5-22 is no ordinary planet. Discovered in 2013, it’s a “rogue planet”: an extrasolar object that doesn’t orbit around a star. It could have been gravitationally ejected from a stellar system, or formed on its own by some other method. But being isolated means that astronomers can detect its light directly without it being drowned out by a star’s glare. The astronomers took hundreds of infrared pictures of PSO J318.5-22, which is a gas giant like our Jupiter but with eight times the mass. As they report in The Astrophysical Journal Letters, shifts in its brightness reveal that PSO J318.5-22 is rotating every 5 hours and has multiple layers of thick and thin clouds with temperatures of about 800°C. The researchers say this shows that clouds are probably ubiquitous in planetary objects. They hope their technique will eventually produce weather reports for gas giants orbiting distant stars and, one day, rocky exoplanets similar to our own.
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