# Evidence of Titanate Clouds in the Day-side Atmosphere of the Ultra-Hot Jupiter WASP-121b

## TL;DR

This study provides the first direct evidence of Titanate clouds in the day-side atmosphere of the ultra-hot Jupiter WASP-121b, using JWST observations to analyze its molecular composition and cloud properties.

## Contribution

It reports the first detection of Titanate (CaTiO3) clouds in an exoplanet atmosphere and offers detailed molecular abundance measurements of WASP-121b.

## Key findings

- Detection of H2O, CO, SiO, TiO, VO at high significance levels
- First confirmed presence of Titanate clouds in an exoplanet atmosphere
- Determination of super-solar C/O ratio and sub-solar Si/O ratio

## Abstract

The day-side atmospheres of the hottest ultra-hot Jupiters (UHJs) have long been subject to speculation about cloud formation, often without direct observational evidence. Here, we present a detailed analysis of the panchromatic day-side emission spectrum of WASP-121b$\unicode{x2014}$one of the hottest known UHJs$\unicode{x2014}$covering a broad wavelength range of $\sim$0.6-5.1$\unicode{x00B5}$m, based on archival JWST observations from NIRISS and NIRSpec/G396H. We report statistically significant detections of several key molecular species, including H$_2$O (13.4 $\sigma$), CO (14.7 $\sigma$), SiO (4.9 $\sigma$), TiO (5.4 $\sigma$), and VO (6.6 $\sigma$), establishing WASP-121b as one of the most thoroughly characterized exoplanetary atmospheres to date. Additionally, we present the robust detection of Titanate (CaTiO$_3$) clouds at 6.7$\sigma$$\unicode{x2014}$the first such detection in any exoplanet atmosphere. Our analysis further reveals strong evidence of TiO depletion, likely due to sequestration into refractory condensates such as Titanate clouds. The precisely constrained molecular abundances yield a super-solar C/O ratio of 0.963$\pm$0.024, a sub-solar Si/O ratio of 0.034$\pm$0.024, and a metallicity of 4.7$_{-1.38}^{+1.99}$ $\times$solar. These findings offer a unique window into the atmospheric chemistry of an extreme UHJ, positioning WASP-121b as a key benchmark for next-generation models of atmospheric evolution and dynamics.