Complex and exotic: astronomers have gained a glimpse of the gas envelope of the exoplanet WASP-189b. In addition to information on the substances it contains, it is apparent that it has layers, similar to the earth’s atmosphere. In the case of the extremely hot, Jupiter-like planet, however, the gas envelope has extremely exotic features: Titanium oxide probably takes over the role of ozone in the stratification. According to the researchers, the results could now also benefit atmospheric research on other exoplanets – including Earth-like worlds.
The cosmos is teeming with stars with planetary satellites – this has been impressively demonstrated by the successes of the planet hunters in recent decades. Astronomers have already been able to record the masses, sizes and thus the densities of many exoplanets, which in turn allows conclusions to be drawn about their compositions. Meanwhile, the curious gaze is directed more and more towards the atmospheres. Insights into their features are possible through spectral analysis of the light that shimmers through the gas envelopes as the distant worlds pass in front of their host star. Signatures in the radiation can allow conclusions to be drawn about the occurrence of certain substances in the atmosphere.
Hellish research object
One of the most extreme known exoplanets was now the focus of an international team of astronomers led by Bibiana Prinoth from the University of Lund in Sweden. WASP-189b is a Jupiter-like celestial body located about 322 light-years from Earth. What is special: Observations with the CHEOPS space telescope revealed that the planet orbits its parent star 20 times closer than Earth orbits the sun. In just 2.7 days, he zooms around him once. Its temperatures are correspondingly hellish: according to estimates, it reaches 3200 degrees Celsius on its day side.
The researchers have now obtained the current insights into the atmosphere of WASP-189b using the HARPS spectrograph at the La Silla Observatory in Chile. “We measured the light from the host star penetrating the planet’s atmosphere. Gases in its atmosphere absorb part of the starlight, similar to how ozone absorbs part of the sunlight in the Earth’s atmosphere, leaving behind its characteristic ‘fingerprint’,” explains Prinoth. “With the help of HARPS, we were then able to identify the corresponding substances in the atmosphere.”
Atmospheric structures emerge
Based on the signatures in the radiation, the scientists were able to detect iron, chromium, vanadium, magnesium and manganese in the gas envelope of WASP-189b. But the most important discovery is that the atmosphere contains titanium oxide. So far, this connection could at least not be proven with certainty in ultra-hot gas giants. The interesting thing about titanium oxide is that the substance, which is rare in our country, could play an important role in the atmosphere of WASP-189b – similar to that of ozone in the stratification of the earth’s atmosphere. “Titanium oxide absorbs short-wave radiation, such as ultraviolet radiation. Its discovery could therefore point to a layer in the atmosphere of WASP-189b that interacts with stellar radiation in a similar way to the ozone layer on Earth,” explains co-author Kevin Heng from the University of Bern.
The researchers also found further evidence of structuring in the gas envelope of the exoplanet: When examining the so-called line positions of the atmospheric components, they found characteristic variations. “In our analysis, we saw that the signatures of the different gases were slightly altered compared to our expectation. This suggests, in our opinion, that they occur in different strata. Similarly, the fingerprints of water vapor and ozone on Earth would appear differently altered from a distance because they mostly occur in different atmospheric layers of our planet,” explains Prinoth. The results thus show that WASP-189b also has a stratified atmosphere in which three-dimensional processes, thermal effects and dynamics play an important role.
advances in atmospheric research
The study could change the way exoplanets are studied, the scientists say. “Until now, astronomers have often assumed that the atmospheres of exoplanets exist as a unified layer and have attempted to understand them as such. However, our results make it clear that the atmospheres of intensively irradiated gas giant planets also have complex three-dimensional structures,” says co-author Jens Hoeijmakers from Lund University. Prinoth adds: “With our study, we are paving the way to gaining a much deeper understanding of exoplanet atmospheres with high-resolution spectrographs.”
As more and more technical tools become available, it will be possible to better understand the chemical composition of different types of exoplanet atmospheres. “We are convinced that we have to take into account the three-dimensional nature of the atmospheres in order to be able to fully understand them,” says Heng. Prinoth is also targeting the Earth-like and possibly life-friendly candidates: “I’m often asked if I think my research is relevant to the search for life elsewhere in the universe. My answer is always yes. These types of studies represent steps in this quest,” the astronomer said.
Source: University of Lund, University of Bern, specialist article: Nature Astronomy, doi: 10.1038/s41550-021-01581-z