Over 1,000 light-years from Earth is a monstrous gas giant of a planet—500 times more massive than our own—where clouds seem to be made from corundum, the same mineral that creates rubies and sapphires here on Earth. This conjures up the image of a glittering disco ball of a planet, but HAT-P-7b, as it's called, isn't anyplace you'd want to visit. It's wracked by catastrophic storms, ferocious winds, and temperatures that reach a scalding 2,500℃ and higher on its day-facing side (the planet is tidally locked with its host sun).
This is according to a new study in Nature Astronomy, in which scientists managed to observe weather systems on a gas giant outside our solar system for the first time.
"Because it's a gas giant, it has a lot of atmosphere. It's almost all atmosphere," lead author David Armstrong of the University of Warwick's Astrophysics Group told me in an interview. Using NASA's Kepler space telescope, his team was able to track light bouncing off the atmosphere of HAT-P-7b, which is what scientists call a "Hot Jupiter"—a gas giant like our solar system's kingpin, but one that squeezes in close to its star.
Looking over all four years of Kepler data, they observed dips in the light reflecting off this planet that indicated a shifting bright point, which is thought to be caused by a jetstream driving massive amounts of cloud across its face, and probably causing some mindboggling storms along the way.
These clouds, if they contain corundum, wouldn't literally be studded with sapphires and rubies, of course. "Because this planet is so hot, it would have very different materials" than on Earth, Armstrong told me, and corundum—which gives the gemstones their colour—is a likely candidate.
So would the clouds be red? "It depends on what else is in the atmosphere," he said. "We don't know the colour, but it would certainly be stunning."
Armstrong described a scene of massive cloud banks coursing over towards the day side of the planet, where they'd be lit by the host star and evaporate. While we don't know how fast winds would whip across the planet, they likely travel "kilometers a second," he said.
It's not the first time we've heard of a planet described as being jam-packed with gemstones. Years ago, scientists reported that one outside of our solar system called 55 Cancri e might be mostly made of diamond, although they later revised that.
Armstrong wants to continue to study HAT-P-7b, and look at weather systems on other exoplanets, too. (Using Kepler to do this isn't possible for more than a handful, though. Planets need to be extremely hot gas giants for the technique to work.)
As for whether he'd ever want to visit, well, "it's a hellhole," Armstrong said. So probably not. A sky of gaseous sapphires and rubies is something to observe from afar.
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