When you think of air, you don't typically think of metal, but that's probably because you aren't on WASP-189b. To be clear, you'd also be very dead if you were.
WASP-189b is an exoplanet orbiting a star about 322 light-years away from us and it's what astronomers call a "hot Jupiter." Unlike our own gas giants, which orbit the sun on the outer part of our solar system, hot Jupiters are gas giants that orbit closely to their host stars. WASP-189b, for example, is about 20 times closer to its star as we are to the sun.
This produces very hot atmospheric temperatures on the daytime side of the planet, upward of 3,200 degrees Celsius. This is hot enough to boil metals like iron, chromium, and magnesium, which brings these elements into their gaseous states and allows them to create a layered atmosphere around the planet.
Researchers at the University of Bern, University of Geneva, and Lund University in Sweden discovered the extraordinary chemical composition of WASP-189b's atmosphere using data from the Characterising Exoplanets Satellite (CHEOPS) space telescope and the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrograph at Chile's La Silla Observatory.
"We measured the light coming from the planet’s host star and passing through the planet’s atmosphere," Bibiana Prinoth, a doctoral student at Lund University and the lead author of a new study in Nature Astronomy detailing the discovery, said in a statement.
"The gases in its atmosphere absorb some of the starlight, similar to ozone absorbing some of the sunlight in Earth’s atmosphere, and thereby leave their characteristic ‘fingerprint.’ With the help of HARPS, we were able to identify the corresponding substances.”
Among those identified were iron, chromium, vanadium, magnesium, and manganese. Also spotted was titanium oxide, which is particularly interesting to researchers.
"Titanium oxide absorbs short wave radiation, such as ultraviolet radiation," said study co-author Kevin Heng, a professor of astrophysics at the University of Bern. "Its detection could therefore indicate a layer in the atmosphere of WASP-189b that interacts with the stellar irradiation similarly to how the Ozone layer does on Earth."
Analysis: Extreme exoplanets challenge us to think differently about the universe
After spending centuries looking at the planets of our own solar system, we've developed something of a baseline for what we consider to be extreme environments, like Venus' crushing carbon dioxide atmosphere and runaway greenhouse effect trapping in temperatures of nearly 482 degrees Celsius.
The more we look at exoplanets though, the more apparent it becomes that Venus and Jupiter are only a glimpse of how drastic conditions on other worlds might be.
The idea of a hot Jupiter hadn't been considered until we first started identifying exoplanets out in the galaxy and found that not only do they exist but are pretty common.
Planets with metallic atmospheres shouldn't be any more of a surprise when you consider the abundance of iron in the universe. After all, it has a boiling point well below the temperature that most stars are capable of producing even at a significant distance, so it's perfectly logical that you're going to find planets with iron atmospheres.
It doesn't make it any less weird to contemplate, though, and part of the fun of learning about exoplanets is finding out just how weird the universe can be.
