Artist’s impression of iron rain on WASP-76b ESO/M. Kornmesser

An exoplanet similar to Jupiter could have the ultimate bad weather: iron rain.

“It showcases probably one of the most extreme planetary climates we’ve ever seen,” says David Ehrenreich at the University of Geneva in Switzerland.

The planet is called WASP-76b and is about 390 light years away from our solar system. It is a gas giant similar to Jupiter, but with a much shorter orbit around its star, fewer than two Earth days. It always faces its star on the same side, and because it is orbiting so close, the day side is about 1000°C hotter than the night side, reaching temperatures of about 2400°C.


This means the side facing towards Earth is too dark to be seen by telescope, but a small amount of starlight filters through the planet’s atmosphere, revealing the outer edges.

The team analysed this light and detected a signal of gaseous iron, which is also found in the atmospheres of other ultra-hot Jupiters.

Read more: First exoplanet weather report shows clouds of ruby and sapphire

WASP-76b’s iron signal, however, was unevenly distributed, present during the planet’s evening transition from day to night but not from night to day. The team could discern this from the amount of light they saw on either side of WASP-76b, which correspond to the boundaries between day and night.

Because the evening transition results in a drastic temperature drop, the team thinks the iron condenses into clouds when it reaches the darker, colder side of the planet, which could mean that it rains liquid iron droplets during WASP-76b’s night time.

It seems likely that iron rain is present on WASP-76b, says David Armstrong at the University of Warwick, UK. Whether other ultra-hot Jupiters have the same weather will depend on the wind speed and the temperature difference between the day and night side, he says.

Journal reference: Nature, DOI: 10.1038/s41586-020-2107-1

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