Located 390 light-years away from Earth is WASP-7 6b, a new giant exoplanet slightly less massive than Jupiter but swollen and fluffier and about 1.9 times the size of the fifth planet in the solar system. , which registers during the day temperatures that exceed 2 400 ºC , a heat more than enough to allow precipitation of metals such as iron: metals evaporate at such high temperatures.
Metallic steam
An international team of scientists with the participation of the Higher Council for Scientific Research (CSIC) has located it in the constellation of Pisces. The funny thing is that their faces are fixed due to being tidal-locked to their star. It takes as long to rotate around its axis as it does to rotate around the star, in a dizzying orbit of just 1.8 days . Regarding its fixed faces: the daytime side has temperatures of 2400ºC and at night, the strong winds transport the iron vapor until it falls in the form of drops.
And it is that on the day side, the planet receives thousands of times more radiation from its parent star than the Earth from the Sun. It is so hot that molecules separate into atoms and metals such as iron evaporate into the atmosphere. The extreme temperature difference is palpable: at night they drop to around 1,500 ºC. And it is that the colder side remains in perpetual darkness.
WASP-76b, which is 1.5 times the mass of the Sun, not only has different day-night temperatures, it also has different chemistry during the day and at night.
“You could say that on this planet it rains at night, except that it rains iron,” explained David Ehrenreich, an astronomer at the University of Geneva and leader of the work that publishes the journal Nature .
Ultra-hot gas giant
These kinds of worlds “are weirdos” of the cosmos. They are expelled with so much radiation from their suns that their daytime temperatures rival some stars. Meanwhile, the night sides of ultra-hot gas giants tend to be much softer.
The team used the Very Large Telescope in Chile to examine the filtering of starlight through WASP 76b’s atmosphere as the exoplanet passed in front of its sun during two orbits in 2018. Those observations revealed the chemical components of different regions of the atmosphere. While the atmosphere showed traces of iron gas where the planet was transitioning to night (at the night terminator), no iron was detected at the night-to-day transition (at the morning terminator), suggesting the iron condensation into liquid raindrops. So considering it is a gaseous planet, there is no land to form puddles of iron, so researchers suspect that these iron raindrops reach such great depths that they vaporize back into iron gas. iron.
WASP 76b is not the hottest exoplanet we have ever discovered . It holds the KELT-9 B record, a world so hot it’s … literally evaporating.
We will have to see what other unusual worlds we will find when the long-awaited James Webb space telescope is underway. Its launch is scheduled for 2021.
Referencia: David Ehrenreich et al. Nightside condensation of iron in an ultrahot giant exoplanet, Nature (2020). DOI: 10.1038/s41586-020-2107-1 , https://www.nature.com/articles/s41586-020-2107-1
