Sub-Neptune exoplanets are the most abundant type of planet known today. As they do not have a Solar System counterpart, many open questions exist about their composition and formation.
![Results of the pRT retrievals for the atmosphere of HD 86226 c. Left: PACMAN spectrum (black data) and 1, 2, and 3σ percentiles of the spectra from the posteriors of the pRT retrieval with scaled solar chemistry (green shadings). The gray spectra show cloud-free models with 1× and 1000× solar metallicity. Right: Posterior distribution for the two retrieval runs with scaled solar chemistry (green) and H-He-H2O atmosphere (purple). The pressures are provided in units of log10([bar]). Contours are drawn at the 1, 2, and 3σ levels. Vertical dashed lines mark the 16%, 50%, and 84% quantiles. astro-ph.EP](https://i0.wp.com/astrobiology.com/wp-content/uploads/2025/07/The-SPACE-Program-I.png?resize=1200%2C709&ssl=1)
Sub-Neptune exoplanets are the most abundant type of planet known today. As they do not have a Solar System counterpart, many open questions exist about their composition and formation.