So Metal: This Exoplanet Rains Droplets of Molten Iron

Strong winds that swirl around these planets take iron in vapor form and swirl it over to the cooler always-dark side; much like water rain precipitates out of water vapor when it cools on Earth, iron droplets condense out of the iron vapor, raining iron there.

The permanent day side is "roasted" and is so hot all clouds are dispersed as the molecules are turned into their individual atoms.

The hot gas giant circles a star roughly 640 light-years away in the Pisces constellation. Using the new ESPRESSO instrument on ESO's VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. Despite being cooler on the night side of the planet, temperatures are still scorching, and hover at around 1,500 degrees Celsius, meaning that the liquid metal falling from the sky would be mighty uncomfortable.

For comparison the closest planet to the Sun, Mercury, orbits our star every 88 days.

ESPRESSO was originally created to hunt Earth-like planets around Sun-like stars. Iron is vaporized due to high daytime temperatures and then condenses into rain as it moves to the cooler night side, becoming rain.

When the evening transition happens, iron vapor is detectable in the planet's atmosphere. The "sunny" side is blasted with hot temperatures that are estimated to be around 2,400°C. "Surprisingly, however, we do not see the iron vapor in the morning", Ehrenreich notes.

The information about this planet was collected using the VLT's new ESPRESSO, or Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations, instrument.

The astronomers were able to detect the chemical differences using the very first scientific observations done with ESPRESSO by a team from Portugal, Italy, Switzerland, Spain and ESO in September 2018.

Astrophysicists observed the strongest iron signatures found in the planet's atmosphere during the evening, along the day and night side barrier, which suggests each side has its own unique chemistry.

'We soon realised that the remarkable collecting power of the VLT and the extreme stability of ESPRESSO made it a prime machine to study exoplanet atmospheres, ' says Pedro Figueira, ESPRESSO instrument scientist at ESO in Chile.

"What we have now is a whole new way to trace the climate of the most extreme exoplanets", concludes Ehrenreich.

The insane weather on the planet is due to the way it rotates around its parent star. "A fraction of this iron is injected at night due to the rotation of the planet and atmospheric winds".

Theoretical studies show that a planet, like WASP-76b, with an extremely hot day side and colder night side would have a very big condensation front in the form of a cloud cascade at its evening border, the transition from day to night, as depicted here.

'There, the iron encounters much cooler environments, condenses and rains down'.