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Each exoplanet with its peculiarities? In this rain it rains in the late afternoon

With the help of ESO's Very Large Telescope (VLT), researchers from several countries, including Portugal, observed an extreme planet where iron is thought to rain. The WASP-76b, an ultra-hot giant exoplanet has a diurnal side where temperatures rise to 2400 Celsius, that is, high enough to vaporize metals. Strong winds carry iron vapor to the cooler night side, where this vapor condenses into drops of iron.

We can say that this rainy planet in the late afternoon, the difference is that the rain of iron, said David Ehrenreich, a professor at the University of Geneva, Switzerland, who led a study published today in the journal Nature, about this exotic exoplanet located about 640 light years away from Earth, in the Pisces constellation.

This strange phenomenon occurs because the planet of the iron rain only shows one face, the day side, its progenitor star, the night side being always in darkness. Like the Moon orbiting the Earth, WASP-76b is in synchronized rotation, which means that it takes as long to complete a rotation around its axis as it does to spin around its star, explained in an ESO statement.

According to the new study, WASP-76b not only has different temperatures between the day and night sides, but also has a different chemistry between the two sides. The discovery was made thanks to the ESPRESSO instrument mounted in the ESO VLT, located in the Chilean Atacama desert.

Observations show that iron vapor is abundant in the atmosphere on the hot day side of WASP-76b. A fraction of this iron is injected on the night side, due to the rotation of the planet and the atmospheric winds. A, iron finds much colder environments, which causes it to condense and precipitate.

These results were obtained in September 2018, from the first scientific observations of ESPRESSO, by the scientific consortium that built the instrument: a team from Portugal, Italy, Switzerland, Spain and ESO.