Scientists have spotted the first evidence of an alien world with an atmosphere that's layered like Earth's — although perhaps a little too toasty for human tastes.
The planet, dubbed WASP-189b, isn't a new discovery. Scientists already knew that the world, which lies about 322 light-years from Earth, is a gas giant that orbits its star 20 times closer than Earth does the sun, making it a sweltering world. And in a new study of the exoplanet, scientists found the first hint that such a body sports a complex atmosphere like our own.
"In the past, astronomers often assumed that the atmospheres of exoplanets exist as a uniform layer," Jens Hoeijmakers, an astrophysicist at Lund Observatory in Sweden and a co-author on the new research, said in a statement released by the University of Bern in Switzerland, where some of the scientists are based. "But our results demonstrate that even the atmospheres of intensely irradiated giant gas planets have complex three-dimensional structures."
The research is based on analyzing light from the planet's star, WASP-189, as the world passes in front of it. Specifically, the scientists used observations gathered in 2019 by the High Accuracy Radial Velocity Planet Searcher (HARPS) instrument at La Silla Observatory in Chile during three different passes of the planet in front of its star.
By looking at the ring of light immediately surrounding the planet's shadow, scientists can study the atmosphere without seeing it directly. In this technique, researchers first determine what wavelengths of starlight don't reach the instrument, then they identify what chemicals absorb that characteristic "fingerprint" of light.
HARPS can't directly distinguish how those chemicals are arranged within an atmosphere and the scientists didn't observe layering firsthand. However, the chemical fingerprints detected are influenced by the same Doppler effect that makes a siren sound differently when approaching and leaving. In their analysis, the researchers found slightly different Doppler effects among different chemicals, suggesting that they were moving differently through the atmosphere and that it therefore has a complex structure.
"We believe that strong winds and other processes could generate these alterations," Bibiana Prinoth, lead author of the study and doctoral student at Lund University, said in the statement. "And because the fingerprints of different gases were altered in different ways, we think that this indicates that they exist in different layers — similarly to how the fingerprints of water vapor and ozone on Earth would appear differently altered from a distance, because they mostly occur in different atmospheric layers."
Among the specific chemicals the team identified was one of particular interest, titanium oxide, which the researchers think could be absorbing short-wavelength light, as Earth's ozone layer does.
Also in the atmosphere of WASP-189b, according to the new study, are a handful of different metals, including iron, chromium, magnesium and vanadium. While we humans don't usually think of metals as being gaseous, given the temperatures at WASP-189b, it's not surprising. The planet's star is particularly hot, and the planet is so close it takes just 2.7 Earth days to orbit, according to previous research.
"We are convinced that to be able to fully understand these and other types of planets — including ones more similar to Earth — we need to appreciate the three-dimensional nature of their atmospheres," Kevin Heng, an astrophysicist at the University of Bern and co-author on the new research, said in the statement. Fortunately, the newly launched James Webb Space Telescope is equipped to do this kind of atmospheric detective work as well.
The research is described in a paper published Thursday (Jan. 27) in the journal Nature Astronomy.