Ruby rains of the exoplanet HAT-P-7b

HAT-P-7b (or Kepler-2b) is an extrasolar planet discovered in 2008. It orbits very close to its host star HAT-P-7 located about 1044 light-years away in the constellation Cygnus, and is both larger and more massive than Jupiter.
In December 2016, a letter published in Nature Astronomy by Dr. David Armstrong and his colleagues described evidence of strong wind jets of variable speed on HAT-P-7b. High variation in wind speed would explain similar variations in light reflected from HAT-P-7b's atmosphere. In particular, the brightest point on the planet shifts its phase or position on a timescale of only tens to hundreds of days, suggesting high variation in global wind speeds and cloud coverage. Condensation models of HAT-P-7b predict precipitation of Al2O3 (corundum) on the night side of the planet's atmosphere. Because corundum gems are rubies and sapphires, one can describe the hypothetical weather on the planet's night side as "raining rubies and sapphires."

Wikipedia

Variability in the atmosphere of the hot giant planet HAT-P-7 b

12 December 2016

First exoplanet weather report shows clouds of ruby and sapphire

By Rebecca Boyle

It’s cloudy with a chance of gemstones. A super-sized planet 1000 light years from Earth has clouds that may contain the building blocks of rubies and sapphires, according to the first exoplanet meteorology report.
The planets in our solar system experience a wide variety of weather, from Jupiter’s famous Great Red Spot through Mars’s dust devils to Saturn’s hexagonal north polar storm. But planets around other stars are too distant for us to directly discern their short-term weather, such as changes in clouds or wind.
Now, David Armstrong at the University of Warwick, UK, and colleagues scrutinised four years of data from the Kepler satellite, and noticed that the brightness of a planet called HAT-P-7b changed over time.
“With this four-year timeline, you can really start to look in depth at these planets,” says Hannah Wakeford, who studies exoplanet atmospheres at the NASA Goddard Space Flight Center in Greenbelt, Maryland, and was not involved in the work. “Our full understanding of these planets and the clouds in their atmospheres is just beginning.”
Vaporised minerals
The planet is about 40 per cent larger than Jupiter and is baked to a searing 2200 degrees kelvin (1900 °C), in part because it’s so close to its star – it completes an orbit every two days. Armstrong and colleagues found the brightest areas on the planet moved around with time, which they say is due to changes in cloud coverage around the world.
The planet is locked in position, so it shows the same side to the star, the way the moon always displays the same face to Earth. As a result, the planet’s day side is much hotter than its night side. Clouds could condense on the cooler night side, and the temperature difference would create winds that send the clouds streaming around the planet.
“The winds transport clouds from the night side, so the cloud bank stretches some way into the day side before finally evaporating,” Armstrong says. As the clouds evaporate, the planet absorbs more light and warms up, strengthening the winds.
“When we say clouds, they’re definitely not clouds like on the Earth,” Armstrong says. The planet is so hot that minerals would be vaporised.
Based on its boiling point, Armstrong says the clouds are likely made of corundum, the same mineral that produces sapphires and rubies on Earth. But more detail is needed to determine the clouds’ exact make-up.
Eventually, more powerful telescopes like the James Webb Space Telescope and the European Space Agency’s PLATO telescope will be able to study those clouds, and potentially search for signs of life in exoplanet atmospheres. But Wakeford says there’s plenty of exoplanet meteorology to do in the meantime.
“Maybe in all the other stars that Kepler looked at, there is something else we haven’t quite discovered yet,” she says.