Glossy silicate clouds discovered on the dayside of ultra-hot planet LTT 9779 b

Star system: LTT 9779 | Distance from the Sun: 264 light years

LTT 9779 b is an ultra-hot Neptune-sized planet orbiting in a region of space known as the Neptunian desert, where such worlds are typically not found. Recent observations have provided the first clear evidence of clouds on the dayside of this planet. These clouds, made of silicate—a common mineral found in rocks—act as a highly reflective layer, explaining why the planet appears so bright when viewed from space.

The analysis confirms that the planet's high reflectivity, or albedo, is caused by these glossy cloud decks rather than an unusually metal-rich atmosphere. This finding settles a long-standing question about the composition of the planet’s upper atmosphere.

Researchers utilized data from the James Webb Space Telescope to examine the light filtering through the planet's atmosphere. By analyzing this light, they identified signatures of carbon monoxide and carbon dioxide, while also measuring the ratio of carbon to oxygen.

The high carbon-to-oxygen ratio observed suggests that oxygen is trapped within these mineral-rich clouds, a trend previously seen in much larger ultra-hot gas giant planets. This indicates that extreme heat processes drive similar chemical environments across different types of planets.

Key findings
- First statistical detection of clouds on the dayside of a Neptune-mass exoplanet.
- Clouds are composed of magnesium silicate (Mg2SiO4).
- Reflective clouds explain the planet's high brightness.
- Robust detection of carbon monoxide and carbon dioxide in the atmosphere.
- Carbon-to-oxygen ratio measured at 0.984.

Scientific study

Glossy Silicate Clouds on the Scorched Dayside of LTT9779b (external link)