Climate simulations of exoplanet Ross 128 b suggest low reflectivity for rocky worlds

Star system: Ross 128 | Distance from the Sun: 11 light years

The exoplanet Ross 128 b, which orbits a nearby Red dwarf star, serves as a primary model for understanding the atmospheres of rocky worlds. By simulating various climate conditions and atmospheric compositions, new research assesses how these planets reflect light, a critical factor for future observations using high-contrast imaging and high-resolution spectroscopy—techniques that separate a planet's light from its host star to analyze its atmosphere.

The research team utilized three-dimensional global climate models to evaluate how factors such as surface pressure, water levels, and rotation influence the planet's environment. These simulations allowed the researchers to generate synthetic reflectance spectra to predict how light interacts with the planet under different conditions.

The findings indicate that rocky planets receiving high levels of irradiation, like Ross 128 b, likely possess low reflectivity, or geometric albedo. Values calculated for specific spectral bands range between 0 and 0.2, significantly lower than the 0.3 albedo often assumed for Earth-like planets. This low reflectivity is likely caused by a lack of clouds or surface ice on the day-facing side of the planet, or by strong absorption of light by water vapor in the atmosphere.

These results suggest that relying on generic albedo assumptions may lead to overestimations of how bright these exoplanets appear. Precise climate modeling is therefore essential for optimizing the design and observation strategies for upcoming instruments on next-generation telescopes.

Key findings
- Ross 128 b shows low geometric albedo between 0.07–0.2 in the RISTRETTO band and 0–0.14 in the ANDES band.
- Low reflectivity is driven by an absence of clouds, lack of surface ice, or strong water vapor absorption.
- Current Earth-like reflectivity assumptions of 0.3 likely overestimate the brightness of similar rocky exoplanets.
- Advanced 3D climate models are necessary to accurately predict spectral signatures for future high-contrast imaging missions.

Scientific study

A broad exploration of climate and observability of close-in rocky exoplanets: applications to Ross 128 b (external link)