Discovery of an extremely hot exoplanet in which could rain iron

2020-03-11

Figure: artistic impression of the atmosphere of the planet WASP-76b. ©ESO


An international team led by the University of Geneva and with the participation of the Centro de Astrobiología (CAB, CSIC-INTA) and the Instituto de Astrofísica de Canarias, has discovered a giant exoplanet with daytime temperatures are capable of vaporizing iron, which could condense into raindrops in the night regions. The finding has been made possible by the new ESPRESSO instrument, installed in the European Southern Observatory (ESO) VLT telescope.


Researchers have used ESO's Very Large Telescope (VLT) located in Cerro Paranal, in Chile's Atacama desert, to observe the EXOplanet WASP-76b, located about 640 light-years away from Earth, in the constellation Pisces. It is an extremely hot giant exoplanet, with daytime temperatures rising above 2400ºC, high enough to vaporize metals such as iron. Strong winds move iron vapour into cooler night regions with temperatures decreasing to around 1500ºC, which condense steam into droplets that could precipitate like rain. "You could say that this planet becomes rainy at night, except that it rains iron," explains David Ehrenreich, a researcher at the University of Geneva and lead author of the study published today in the journal Nature.

WASP-76b not only presents noticeable temperature differences between day and night faces, but also has a distinct chemistry in both regions, according to the new study. Using the new ESPRESSO instrument (Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscpic Observations) installed on the VLT, researchers first identified chemical variations on a giant exoplanet. The unequivocal signature of the presence of iron vapour in the terminator area, the frontier of the planet where it is passed from day to night, has been detected.

The observed phenomenon is because the exoplanet always shows the same face to its host star, remaining in perpetual night on its hidden face. This situation, known as 'tidal coupling', is the same as that between the Moon and Earth, and in it the time it takes for the exoplanet to rotate around its axis coincides with the time it takes to travel its orbit around the host star. The WASP-76b exoplanet receives thousands of times more radiation from its host star than Earth of the Sun, causing the temperature on its daytime face to be so high that molecules separate into atoms, and metals like iron in the vapour-shaped atmosphere.

As Maria Rosa Zapatero Osorio, CAB researcher and coordinator of the ESPRESSO scientific team, points out, "observations show that iron vapour is abundant in the atmosphere of the daytime and hot face of WASP-76b. A portion of that iron is injected into the dark face of the planet due to its rotation and atmospheric winds. There, it encounters a hugely cooler environment, condenses and precipitates."

The ESPRESSO instrument was originally designed to discover Earth-like exoplanets around Sun-like stars, however, it has proven to be much more versatile. "What we have now is a whole new way to track the climate of the most extreme exoplanets," Ehrenreich concludes.

 

Fuente: UCC-CAB

Fecha: 2020-03-11

 

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