The more exoplanets astronomers discover the more they find that the universe is filled with extraordinary and unusual worlds. A prime example would be WASP-76b, which an international team of astronomers led by researchers from the University of Geneva (UNIGE) have discovered possesses one-side that is brutally bombarded by iron-rains, whilst the other is mercilessly roasted by radiation from the planet’s star.

The giant exoplanet — part of a new category of bodies called ‘ultra-hot Jupiters’ — has a scorching hot ‘dayside’ where temperatures can reach in excess of 2,40⁰⁰C, and a ‘nightside’ which is cooler by at least 1,00⁰⁰C. This means that on the former side, metals are vaporized by the ultra-hot temperatures and then carried across the planet by powerful winds. Once reaching the cooler side, the resulting iron vapor condenses into droplets of iron which rain down onto the surface of the planet.

Geneva cartoonist Frederik Peeters takes a whimsical look at a hellish landscape. Image credit: Frederik Peeters

“These planets are so hot that we are expecting molecules to disassociate into atoms,” explains Romain Allart, PhD candidate and astronomer affiliated to UNIGE and one of the co-authors of a paper discussing the conditions on WASP-76b. “This means they are great laboratories to understand the on-going chemistry in exoplanets’ atmospheres.”

The team was able to discover details of turbulent dichotomy on WASP-76b — part of a system with just one star and one planet located 390 light-years from Earth — with the aid of the ESPRESSO instrument connected to the European Space Observatory’s (ESO) Very Large Telescope. The finding represents not just the first results from the ESPRESSO consortium, but also, a surprise for the team of astronomers.

“When we looked to the data we saw this signature of iron coming from the planet that was not really expected but the most surprising result was to see how this signature was varying across the transit,” says Allart. “This last point made us realized that ESPRESSO can study the climate of extreme worlds.”