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How can it rain metal?

The exoplanet WASP-76b has the particularity, like our Moon, of being "locked by gravitation". In other words, its period of rotation on itself is equivalent to its period of revolution around its star. Concretely, this means that the same face is always in the light while the other is systematically in the shade.

On the planet's lit surface, the temperature can rise to over 2400 ° C. Extreme heat which "vaporizes metals like iron in the atmosphere". Strong winds are then responsible for transporting this iron vapor on its opposite side, the one which is always in the shade. Since the temperature on the latter is "only" 1600 ° C, the iron vapor condenses into droplets.

"Iron vapor, abundant in the atmosphere overhanging the lit face, is injected on the night side under the double effect of the rotation of the planet and the atmospheric circulation", specifies Maria Rosa Zapatero Osorio, astrophysicist at the Center of Astrobiology of Madrid.

A promising instrument

This discovery, based on observations dating from September 2018, was made possible by ESPRESSO, the new instrument of the VLT. If this instrument was originally designed to detect Earth-like planets around stars similar to the Sun, it also makes it possible to study exoplanetary atmospheres, which makes it a versatile and promising tool.