CATA researchers detect titanate clouds on ultra-hot exoplanet

Astronomers Suman Saha and James Jenkins from the Center for Astrophysics and Associated Technologies (CATA) and Universidad Diego Portales detected evidence of calcium titanate on the exoplanet WASP-121b for the first time.

A team of astronomers from CATA and researchers from Universidad Diego Portales (UDP) achieved the first detection of calcium titanate (CaTiO₃) clouds in the atmosphere of the exoplanet WASP-121b. This discovery, made using data from the James Webb Space Telescope (JWST), places Chile and CATA at the forefront of exoplanet atmospheric research.

WASP-121b belongs to the Ultra Hot Jupiters (UHJ) class, a rare type of exoplanet that formed far from its star but eventually migrated to a very close orbit without falling into it. “This planet is one of the hottest known, with a daytime temperature reaching ~2900°K. It is a particularly extreme example of giant gas planets that migrate into very close orbits without falling into their star,” explains Suman Saha, Postdoctoral Researcher at CATA and UDP.

The study identified titanate clouds in the planet’s daytime hemisphere for the first time. These clouds form through the condensation, at high altitude, of titanium monoxide (TiO), a material that can withstand very high temperatures and normally remains solid even under extreme conditions. “Only in the extremely hot environments on the daytime side of rare planets such as WASP-121b can TiO remain in a gaseous phase and then condense into calcium titanate (CaTiO₃) clouds,” says James Jenkins, Principal Investigator at CATA and professor at UDP.

This finding also reveals a phenomenon that has never been directly observed: a cycle of titanium rain on the night side of the planet. “The strong atmospheric currents on this planet carry these clouds toward the terminator and the night side, where they precipitate as rain,” explains Saha. These areas are so cold compared to the day side that the precipitated material does not evaporate again, causing a permanent loss of titanium and oxygen in the planet’s illuminated atmosphere.

To complement this detection, the team observed a reduced abundance of TiO and a high carbon-to-oxygen (C/O) ratio on the day side, both of which are consistent with the existence of this cycle. “It has long been hypothesized that there are cycles involving refractory species ( that is, species that are highly resistant to heat and can evaporate and recondense) in UHJs, but our work provides the first statistically significant detection of this phenomenon, making it a historic result for the exoplanet community,” Jenkins notes.

Use of the JWST and CATA’s Geryon-3

The discovery was made possible by observations from the James Webb Space Telescope, using public data obtained from the NIRISS and NIRSpec instruments, which cover a detailed range between 0.6 and 5.1 microns.

This study uses, for the first time, JWST’s panchromatic emission spectroscopy of WASP-121b, a technique that measures the planet’s light at many different wavelengths to identify molecules and clouds. Because this exoplanet is extremely hot, its emission spectrum is exceptionally precise and rich in features across a wide range of wavelengths. This allowed us to break through the typical confusion in interpreting atmospheric phenomena and solidly identify the types of clouds, making this detection particularly robust,” explains Suman Saha.

The team also used the Geryon-3 supercomputer, CATA’s high-performance infrastructure dedicated to large-scale astronomical data analysis. “This tool was essential for the computational tasks of the study, such as reducing the JWST datasets, fitting the spectroscopic light curves, and reconstructing the atmospheric profile. These data occupy large volumes, which makes their analysis, especially when computationally intensive techniques are involved, unfeasible without access to large-scale computational clusters such as Geryon-3,” says James Jenkins.

Relevance for the Chilean scientific community

This study represents the first major discovery of exoplanets based on the JWST led from Chile, placing both CATA and the country at the forefront of exoplanet atmospheric research worldwide. “Chile is already home to some of the most powerful and unique astronomical observatories in the world and has a community dedicated to exoplanet research. However, JWST-based atmospheric studies represent one of the most advanced frontiers in this field, offering opportunities for unprecedented discoveries and helping to build the expertise needed to remain globally competitive,” emphasizes Saha.

The researchers’ next goal will be to analyze a larger sample of similar and diverse exoplanet atmospheres to identify common evolutionary trends. “It will open up new opportunities to study atmospheric evolution in extreme exoplanets, which will help reveal their formation histories and provide a broader and more predictive understanding of the evolution of giant planets,” concludes the CATA researcher.