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from the like-hail-only-much-much-worse dept.
Exoplanet where it rains iron discovered:
Researchers using ESO's Very Large Telescope (VLT) have observed an extreme planet where they suspect it rains iron. The ultra-hot giant exoplanet has a day side where temperatures climb above 2400 degrees Celsius, high enough to vaporise metals. Strong winds carry iron vapour to the cooler night side where it condenses into iron droplets.
"One could say that this planet gets rainy in the evening, except it rains iron," says David Ehrenreich, a professor at the University of Geneva in Switzerland. He led a study, published today in the journal Nature, of this exotic exoplanet. Known as WASP-76b, it is located some 640 light-years away in the constellation of Pisces.
This strange phenomenon happens because the 'iron rain' planet only ever shows one face, its day side, to its parent star, its cooler night side remaining in perpetual darkness. Like the Moon on its orbit around the Earth, WASP-76b is 'tidally locked': it takes as long to rotate around its axis as it does to go around the star.
On its day side, it receives thousands of times more radiation from its parent star than the Earth does from the Sun. It's so hot that molecules separate into atoms, and metals like iron evaporate into the atmosphere. The extreme temperature difference between the day and night sides results in vigorous winds that bring the iron vapour from the ultra-hot day side to the cooler night side, where temperatures decrease to around 1500 degrees Celsius.
Not only does WASP-76b have different day-night temperatures, it also has distinct day-night chemistry, according to the new study. Using the new ESPRESSO[*] instrument on ESO's VLT in the Chilean Atacama Desert, the astronomers identified for the first time chemical variations on an ultra-hot gas giant planet. They detected a strong signature of iron vapour at the evening border that separates the planet's day side from its night side. "Surprisingly, however, we do not see the iron vapour in the morning," says Ehrenreich. The reason, he says, is that "it is raining iron on the night side of this extreme exoplanet."
"The observations show that iron vapour is abundant in the atmosphere of the hot day side of WASP-76b," adds María Rosa Zapatero Osorio, an astrophysicist at the Centre for Astrobiology in Madrid, Spain, and the chair of the ESPRESSO science team. "A fraction of this iron is injected into the night side owing to the planet's rotation and atmospheric winds. There, the iron encounters much cooler environments, condenses and rains down."
[*] ESPRESSO Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations.
Reference:
David Ehrenreich, et al Nightside condensation of iron in an ultra-hot giant exoplanet https://www.eso.org/public/archives/releases/sciencepapers/eso2005/eso2005a.pdf
(No DOI at this time.)
(Score: 2) by GreatAuntAnesthesia on Thursday March 12 2020, @11:01AM (5 children)
Interesting question. My first reaction was "no way, planets are just too damn big to be affected by a little weather", and this is a giant planet so that's probably the case, but it get me thinking.
Imagine the same scenario on a small, rocky planet like Mercury. All that material is being peeled off the day side and deposited on the back. You could end up with a conveyor, with the material on the back gradually working it's way through the volume of the planet to the front again. With a very small planet, you might also end up with a non-spherical shape. Perhaps something a bit more egg shaped.
(Score: 2) by inertnet on Thursday March 12 2020, @11:48AM (3 children)
Rethinking this, I come to the conclusion that it must also depend on distribution of matter. If the planet is all iron, it won't tilt because the center of gravity will just shift. But if matter and/or density differ, then you could get a wobbling planet over time. A tidally locked planet might suddenly tilt if that wobble becomes big enough.
(Score: 2) by Reziac on Friday March 13 2020, @02:43AM (2 children)
That kind of heat will vaporize a lot of materials other than metals. Tho one suspects that everything volatile has already long since evaporated and rained down on the dark side, after which it became more or less static.
And there is no Alkibiades to come back and save us from ourselves.
(Score: 3, Interesting) by GreatAuntAnesthesia on Friday March 13 2020, @11:57AM (1 child)
Indeed. In fact, a visit to the dark side of the planet might reveal different materials arranged in concentric rings on the planet's surface, each material deposited at a different distance from the terminator according to the temperature / pressure at which they solidify and rain down.
(Score: 2) by Reziac on Friday March 13 2020, @02:28PM
Yep, something like that. But it's not going to be perpetual iron rain unless the planet consists of nothing but iron, which seems unlikely.
And there is no Alkibiades to come back and save us from ourselves.
(Score: 2) by JoeMerchant on Thursday March 12 2020, @01:00PM
I'm thinking: Bowler hat, with the rain depositing around the day-night rim. Maybe after billions of years the bowler hat shape might become unstable enough to flip.
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