The strange planet where it rains iron

On the planet Wasp-76b, it rains iron. Researchers from the University of Geneva (UNIGE) and colleagues observed the planet, 650 light years from Earth, using the European Southern Observatory's Very Large Telescope in northern Chile. On the planet's "hot side" that faces it star, temperatures can be above 2,400°C. It's a good thing the residents of Wasp-76b carry tungsten umbrellas. From ESO:

“One could say that this planet gets rainy in the evening, except it rains iron,” says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 640 light-years away in the constellation of Pisces.

This strange phenomenon happens because the 'iron rain' planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is ‘tidally locked’: it takes as long to rotate around its axis as it does to go around the star.

On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It’s so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapour from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500 degrees Celsius.

More: "Nightside condensation of iron in an ultrahot giant exoplanet" (Nature)

illustration: ESO press release