EXOPLANETS
A plethora of weird and wonderful worlds
If the world’s astronomers ever came together and held a competition to name the most metal planet, chances are WASP-76b would be the clear winner. It’s a planet with an atmosphere so extreme, that it rains molten iron.
The gas giant exoplanet is located 390 light-years away from Earth, in the constellation Pisces. It was observed using a new instrument – dubbed ESPRESSO – built by a team at the University of Geneva and fitted to the
Very Large Telescope (VLT), based at the European Southern Observatory (ESO).
WASP-76b is tidally locked, meaning it takes as long to rotate around its axis as it does to go around its parent star. This results in the planet only ever showing one side to the star, leaving its colder night side in perpetual darkness, much like our Moon. This gives it an ultra-hot day side with temperatures regularly reaching 2,400°C, which is high enough to vaporise metals. Strong winds rage across the planet’s surface and carry the iron vapour over to the much cooler night side, where it condenses into iron droplets and falls as rain.
“We thought very early on, that we could use the instrument not only to discover new planets, but also to characterise those that are already known. However, until 2018, we didn’t realise how powerful ESPRESSO really was,” said Francesco Pepe, professor of astronomy at the University of Geneva.
ESPRESSO was built by the astronomy department at the University of Geneva, with help from teams in Portugal, Italy, Switzerland and Spain. Originally designed to hunt Earth-like planets around Sun-like stars, the instrument has proven to be much more versatile
than first anticipated.
“Thanks to this technology, we have a completely new way of tracing the climate of the most extreme exoplanets,” said the University of Geneva’s Prof David Ehrenreich, who led the study. “One could say this planet gets rainy in the evening, except that it rains iron.”