Flat exoplanet spectra can frustrate astronomers because they obscure chemical signatures and make it difficult to distinguish between clouds, haze, and atmospheric gases. Laboratory research discussed during SETI Live aims to improve how scientists interpret these observations for candidate water-rich planets.

University of Arizona researcher Lori Huseby and NASA Goddard scientist Sarah Moran studied how ultraviolet radiation changes photochemical hazes and how those changes affect spectra observed by telescopes including James Webb Space Telescope. Their work focused on GJ 1214 b and LHS 1140 b, candidate water worlds orbiting active red dwarf stars.

Unlike clouds, which form when gases condense into droplets or ice crystals, hazes arise when ultraviolet light breaks atmospheric molecules apart and allows them to recombine into complex solid particles. These particles can hide atmospheric features. To reproduce such hazes, researchers created gas mixtures containing water vapor, nitrogen, carbon dioxide, methane, or carbon monoxide. Plasma exposure produced organic haze films, which were later irradiated with ultraviolet light. The team measured how the materials absorbed and scattered light, then added those optical properties to atmospheric models.

The models Virga and Picasso simulated how haze layers would influence planetary transmission spectra. The results showed that commonly used haze data from Titan may be misleading when applied to water-rich exoplanets. Titan-based models often predict nearly featureless spectra, while the new measurements reveal atmospheric features that might otherwise remain hidden.

The experiments also showed that water-rich atmospheres can produce substantial haze. Some laboratory particles contained complex organic compounds related to amino acids, nucleobases, and sugars. These are not signs of life, but they may participate in prebiotic chemistry. The same techniques are now being used to study early Earth. Overall, the research demonstrates that laboratory measurements are essential for interpreting JWST data, evaluating potentially habitable worlds, and understanding planetary chemical evolution.

For more details, read the full article by SETI Institute and listen to the Live talk.