Astronomers using the HARPS spectrograph confirmed with great accuracy the existence of titanium oxide in the atmosphere of the ultra-hot Jupiter WASP-189b. It is assumed that this compound may be the main reason for the heating of the stratosphere of such exoplanets, along with metal atoms.
What is a hot Jupiter?
Hot Jupiters are gaseous exoplanets that are close to or larger than Jupiter in size and mass, but orbit at a very small distance from their star. They are easier to detect using the radial velocity or transit method, which is why hot Jupiters make up a significant proportion of known exoplanets.
The atmospheres of hot Jupiters have an unusual composition and complex dynamics due to tidal influence and a powerful flux of radiation from the star.
The temperature of the atmosphere
The temperature of the atmosphere decreases with increasing altitude unless there are substances that give rise to a temperature inversion.
In the case of the Earth, ozone acts as such a substance, and in the atmospheres of giant exoplanets exposed to powerful radiation fluxes from their stars, short-wave absorbers will be titanium oxides (TiO) and vanadium (VO).
These compounds were found by spectrometric methods in the atmospheres of hot and ultra-hot Jupiters, but subsequent observations did not allow to confirm these results or to refute them.
Astronomers discovered titanium oxide in the atmosphere of an ultra-hot Jupiter
A group of astronomers led by Bibiana Prinoth of Lund University reported a significant (at 5.6 sigmas) detection of titanium oxide in the atmosphere of ultra-hot Jupiter WASP-189b thanks to high-resolution transmission spectroscopy.
The exoplanet was observed using the HARPS echelle spectrograph installed on the 3.6-meter telescope at the La Silla Observatory.
WASP-189b is located 326 light-years from the Sun and revolves around a bright star of spectral class A. The exoplanet has a mass of approximately 2 Jupiter masses, a radius of 1.6 Jupiter radii, and makes one revolution around the star in 2.7 days. Its temperature has been estimated at 3435 Kelvin, making it one of the hottest exoplanets known today.
Scientists have found in the atmosphere of ultra-hot Jupiter WASP-189b both titanium and titanium oxide (TiO), as well as atoms and ions of other metals (Fe, Fe+, Cr, Mg, Mn, V, Na, Ca, Sc+, Cr + and Ni). Data analysis shows the presence of atmospheric flows on the exoplanet, directed from the dayside to the night side.
In addition, the researchers concluded that the atmospheres of gaseous exogiants subjected to intense radiation from their stars will have a complex and inhomogeneous volumetric structure in which different substances can be located in different layers and under different conditions.
In particular, the condensation of magnesium and chromium in the atmosphere of ultra-hot Jupiter WASP-189b may be limited to latitudinal regions or altitudes where titanium and titanium oxide (TiO) are absent, or they condense under the same conditions, but other processes affect the concentration of titanium.
As more and more ultra-hot Jupiters are being observed with large ground-based telescopes and space observatories, the researchers believe that the correct interpretation of the observed data depends on how theoretical models take into account the processes of global atmospheric circulation and radiative transfer, as well as inhomogeneous chemical composition.
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• Carpineti, D. A. (2022, January 28). First exoplanet with earth-like layered atmosphere discovered – but you wouldn’t want to live there. IFLScience.
• Lazaro, E. de. (n.d.). Astronomers Detect Titanium Oxide and Several Metals in Atmosphere of WASP-189b. Sci-News.
• O’Neill, M. (2022, January 30). Extreme alien world: Strange exoplanet has a complex and exotic atmosphere. SciTechDaily.
• Prinoth, B., Hoeijmakers, H. J., & Kitzmann, D. (2022, January 27). Titanium oxide and chemical inhomogeneity in the atmosphere of the exoplanet WASP-189 b. Nature News.