An international team including researchers from the University of Bern and
the University of Geneva as well as the National Centre of Competence in
Research (NCCR) PlanetS analyzed the atmosphere of one of the most extreme
known planets in great detail. The results from this hot, Jupiter-like
planet that was first characterized with the help of the CHEOPS space
telescope, may help astronomers understand the complexities of many other
exoplanets—including Earth-like planets.
The atmosphere of Earth is not a uniform envelope but consists of distinct
layers that each have characteristic properties. The lowest layer that spans
from sea level beyond the highest mountain peaks, for example—the
troposphere—contains most of the water vapor and is thus the layer in which
most weather phenomena occur. The layer above it—the stratosphere—is the one
that contains the famous ozone layer that shields us from the Sun's harmful
ultraviolet radiation.
In a new study published in Nature Astronomy, an international team of
researchers led by the University of Lund show for the first time that the
atmosphere of one of the most extreme known planets may have similarly
distinct layers as well—albeit with very different characteristics.
An exotic cocktail for an atmosphere
WASP-189b is a planet outside our own solar system, located 322 light years
from Earth. Extensive observations with the CHEOPS space telescope in 2020
revealed among other things that the planet is 20 times closer to its host
star than Earth is to the Sun and has a daytime temperature of 3200 degrees
Celsius. More recent investigations with the HARPS spectrograph at the La
Silla Observatory in Chile now for the first time allowed the researchers to
take a closer look at the atmosphere of this Jupiter-like planet.
"We measured the light coming from the planet's host star and passing
through the planet's atmosphere. The gasses 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," lead
author of the study and doctoral student at Lund University, Bibiana
Prinoth, explains. According to the researchers, the gasses that left their
fingerprints in the atmosphere of WASP-189b included iron, chromium,
vanadium, magnesium and manganese.
An "Ozone layer" on a blisteringly hot planet?
One particularly interesting substance the team found is a gas containing
titanium: titanium oxide. While titanium oxide is very scarce on Earth, it
could play an important role in the atmosphere of WASP-189b—similar to that
of ozone in Earth's atmosphere. "Titanium oxide absorbs short wave
radiation, such as ultraviolet radiation. 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," study
co-author Kevin Heng, a professor of astrophysics at the University of Bern
and a member of the NCCR PlanetS, explains.
Indeed, the researchers found hints of such a layer and other layers on the
ultra-hot Jupiter-like planet. "In our analysis, we saw that the
'fingerprints' of the different gasses were slightly altered compared to our
expectation. We believe that strong winds and other processes could generate
these alterations. And because the fingerprints of different gasses 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," Prinoth explains. These
results may change how astronomers investigate exoplanets.
A different way to look at exoplanets
"In the past, astronomers often assumed that the atmospheres of exoplanets
exist as a uniform layer and try to understand it as such. But our results
demonstrate that even the atmospheres of intensely irradiated giant gas
planets have complex three-dimensional structures," study co-author and
associate senior lecturer at Lund University Jens Hoeijmakers points out.
"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. This requires innovations in
data analysis techniques, computer modeling and fundamental atmospheric
theory," Kevin Heng concludes.
Reference:
Bibiana Prinoth et al, Titanium oxide and chemical inhomogeneity in the
atmosphere of the exoplanet WASP-189 b, Nature Astronomy (2022). DOI:
10.1038/s41550-021-01581-z
Tags:
Space & Astrophysics