Astronomy: It is raining iron on the exoplanet WASP-76b – High-Tech

On WASP-76b, an exoplanet located 390 light years from Earth, it does not rain water but iron. This strangeness was discovered thanks to ESPRESSO, an instrument developed byUniversity of Geneva (UNIGE) and which equips the very large telescope (VLT) of the European Southern Observatory (ESO).

Over 2400 degrees

WASP-76b has the distinction of rotating around its star, showing only one side, like the moon orbiting the Earth. The nocturnal face is bathed in perpetual darkness. It is much colder than the other half of the planet, constantly exposed to the heat of the star.

On the diurnal side, WASP-76b receives thousands of times more radiation from its star than the Earth receives from the Sun, reports UNIGE. The temperature on its surface rises to more than 2400 degrees. It is so hot there that the molecules separate into atoms and the metals, like iron, evaporate into the atmosphere.

Strong winds then push this iron vapor towards the dark side of WASP-76b, where a temperature prevails of about 1500 degrees. A condensation phenomenon occurs when the vapor reaches the nocturnal face of the exoplanet. “In other words, it’s raining iron,” notes Christophe Lovis, researcher at UNIGE.

It is the ESPRESSO instrument which made it possible to note the phenomenon. Astronomers were able to identify, thanks to him, for the first time the chemical variations on a giant gas planet ultra hot. Iron vapor that was detected on the daytime side of WASP-76b is absent on the night side.

The versatility of ESPRESSO

The ESPRESSO spectrograph was however originally built by an international consortium led by UNIGE to hunt Earth-like planets around Sun-like stars. The tool has however proved to be very versatile, capable of characterizing the planets which are already known.

“Until the instrument was put into service in 2018, we did not realize how effective ESPRESSO was in this area,” explains Francesco Pepe, professor in the astronomy department of UNIGE. The spectrograph can be used to study the climate of the most extreme exoplanets.

Iron rains on the planet WASP-76b are the subject of a publication in the specialized journal “Nature”. (ats / nxp)

Created: 03/11/2020, 21h53

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