Lab-cooked alien haze reveals distant water worlds

Scientists have simulated the conditions that allow hazy skies to form on watery exoplanets, a key step in determining how haze disrupts observations with ground-based and space-based telescopes.

The research provides new tools for studying the atmospheric chemistry of exoplanets and will help scientists model how watery exoplanets form and evolve, findings that could help search for life beyond our solar system.

„The big picture is whether life exists outside the Solar System, but trying to answer those kinds of questions requires extensive modeling of all kinds, especially on planets with a lot of water,” the co-author said. Sarah Horst, Associate Professor of Earth and Planetary Sciences at Johns Hopkins. „It’s a big challenge because we don’t have the lab work to do that, so we’re trying to use these new lab techniques to get the most out of the data we’re taking with these big fancy telescopes.”

The team released its findings today Natural Astronomy.

Whether a planet’s atmosphere contains mists or other particles has a significant impact on global temperatures, incoming levels of starlight and other factors that can inhibit or foster biological activity, the researchers said.

The team conducted the experiments in a custom-designed room in Hearst’s laboratory. They are the first to determine how much fog might form on water planets beyond the Solar System, Horst said.

Fog consists of solid particles suspended in gas, and it changes the way light interacts with that gas. Different levels and types of haze can affect how particles travel through the atmosphere, changing what scientists can see about distant planets with telescopes.

„When we try to see if a planet is habitable, the first thing we look for is water. There are already amazing observations of water in exoplanet atmospheres. But our experiments and modeling suggest that these planets are mostly foggy,” he said. Bye bye, a planetary scientist who led the Johns Hopkins research. „This haze actually complicates our observations because it obscures our view of an exoplanet’s atmospheric chemistry and molecular features.”

Scientists study exoplanets with telescopes that look at how light passes through their atmospheres, detecting how atmospheric gases absorb different hues, or wavelengths, of that light. Distorted observations can lead to inaccurate calculations of the amounts of important substances such as water and methane in the air, and the types and sizes of particles in the atmosphere. Such misinterpretations can affect scientists’ conclusions about global temperatures, thickness of the atmosphere and other planetary conditions, Horst said.

The team created two gas mixtures containing water vapor and other compounds thought to be common on exoplanets. They illuminated the compounds with ultraviolet light to simulate how light from a star would start the chemical reactions that form smog particles. They measured how much light the particles absorb and reflect to understand how they interact with light in the atmosphere.

The new data match the chemical signatures of a well-studied exoplanet known as GJ 1214 b more accurately than previous research, demonstrating that nebulae with different optical properties can lead to false interpretations of a planet’s atmosphere.

Alien atmospheres may be very different from those in our solar system, Horst said, adding that there are more than 5,000 confirmed exoplanets with different atmospheric chemistries.

The team is now working to create lab-generated fog „analogs” with gas compositions that more accurately represent what they see through telescopes.

„People can use that data when they’re modeling those atmospheres to try to understand things like the temperature in the atmosphere and what the surface of the planet is like, whether there are clouds, how high they are and what they’re made of, or how fast the wind is going,” Horst said. „All of those kinds of things will help us really focus our attention on specific planets and make our experiments unique instead of generalizing when we’re trying to understand the big picture.”

Other authors include Michael Radke and Sarah E. Moran, Johns Hopkins; Cornell University’s Nicole K. Louis; Julianne I. Moses of the Space Science Institute; University of Arizona’s Mark S. Marley; Natasha E. Batalha of NASA’s Ames Research Center; Eliza M.-R. University of Maryland Kempton, College Park; Carolyn V. of the University of Texas at Austin. Morley; Jeff A. of the Space Telescope Science Institute. Valenti; and Véronique Vuitton of Université Grenoble Alpes.