TOI-561 b has a reflective atmosphere with silicate clouds

The rocky planet TOI-561 b appears to have an atmosphere that reflects much of the energy it receives from its star. A 37-hour record of the planet’s changing infrared brightness points to moderate heat transfer around the globe and silicate clouds forming near the boundary between its day and night sides.

Star system: TOI 561 | Distance from the Sun: 276 light years

TOI-561 b, a rocky planet exposed to intense heat from its star, appears to have a reflective atmosphere. Such close-orbiting planets are expected to lose much of any thick gaseous envelope. Earlier evidence for an atmosphere on this world came from its overall density and the infrared light from its dayside. The planet’s changing brightness across its orbit now points to an atmosphere that reflects a large share of incoming energy and moves some heat around the planet.

The planet’s 3-to-5-micrometer infrared emission was tracked continuously for 37 hours with the James Webb Space Telescope. These full-orbit measurements, called a phase curve, show how a planet’s brightness changes as different regions face Earth. The long record allowed the analysis to separate the planet’s signal from small changes in the star’s brightness, known as granulation, and to account for possible shifts in the hottest region. The resulting dayside spectrum agrees with earlier measurements made when the planet passed behind its star.

Energy calculations and models of atmospheric circulation both favor a high Bond albedo, meaning the planet reflects a large fraction of the total energy it receives, along with moderate heat transfer around the globe. The models also suggest that silicate clouds could form on the dayside near the boundary between day and night. Clouds made of silicon dioxide or magnesium silicate could help explain the planet’s reflectivity. The results support the picture of a reflective atmosphere across the planet and suggest that gases from its interior may help replenish it.

Key findings
TOI-561 b’s infrared brightness was tracked across its orbit during 37 hours of continuous observations.
The phase curve is best explained by a high Bond albedo and moderate heat transfer around the planet.
Accounting for stellar granulation and possible shifts in the hottest region produced a dayside spectrum consistent with earlier measurements.
Models indicate that silicon dioxide or magnesium silicate clouds could form near the dayside boundary between day and night.
The results support a reflective atmosphere and suggest an exchange of gases with the planet’s interior.

Scientific study

A Highly Reflective Atmosphere on the Lava World TOI-561b Revealed by JWST/NIRSpec Phase Curves (external link)