New Exo-REM models reveal patchy clouds on VHS 1256 b

Star system: VHS 1256-1257 A | Distance from the Sun: 69 light years

Researchers have upgraded the Exo-REM atmospheric model to better simulate the complex, patchy clouds found in brown dwarfs and exoplanets. The new Exo-REM k26 grids include a cloud sedimentation parameter, improved molecular opacities, and stricter convergence criteria, allowing for more accurate modeling of objects with heterogeneous cloud cover. Applying this model to VHS 1256 b, a variable brown dwarf, the team found that a two-column approach—representing thick and thin cloud regions—fits the observed spectra much better than traditional single-layer models.

The best fit for VHS 1256 b’s atmosphere is a mix of about 60% thick clouds and 40% thin clouds, which explains the strong 10-micron silicate absorption seen in JWST data. The model also corrects previous errors in methane abundance for cool objects and revises parameters for other substellar objects like GJ 504 b. These advances help explain the observed variability and colors of brown dwarfs and exoplanets, and provide a framework for interpreting future observations.

Key findings
- Exo-REM k26 models simulate patchy clouds using a two-column approach.
- VHS 1256 b’s atmosphere is best described by a 60-40% mix of thick and thin clouds.
- The model reproduces strong silicate absorption features seen by JWST.
- Improved opacities and parameters enhance fits for a range of substellar objects.

Scientific study

Next-generation Exo-REM atmospheric models: application to VHS 1256 b to emulate patchy clouds (external link)