Hundreds of light-years away, there's a planet that looks like a giant mirror. LTT9779b reflects most of the light that hits it — far more than you'd expect from a Neptune-sized body. Astronomers have long debated what makes it so shiny: a thick carbon-rich haze or a layer of clouds.

The James Webb Space Telescope has helped settle the debate. It observed the planet's dayside in the infrared and captured a spectrum with an exceptionally high signal-to-noise ratio. In that spectrum, clear signatures of condensates, tiny solid particles in the atmosphere, emerged. With high confidence (between 3 and 5 sigma), scientists identified these particles as Mg₂SiO₄, magnesium silicate. In other words, on LTT9779b, it rains molten rock.

The cloud layer explains the high reflectivity without invoking an extremely metal-rich atmosphere. Additionally, carbon monoxide (CO) and carbon dioxide (CO₂) were reliably detected in the atmosphere, and the carbon-to-oxygen ratio was estimated. It turned out to be 0.984 ± 0.019—notably higher than the solar value. This links LTT9779b to ultra-hot Jupiters and points to a common mechanism: in scorching atmospheres, oxygen gets locked into refractory particles that sink deeper, while carbon remains in the gas phase. The mirror planet turned out to be a trap for oxygen as well.