An illustration of two water-rich exoplanets with hazy atmospheres. Credit: Roberto Molar Candanosa/Johns Hopkins University.
When its hazy on Earth, it’s merely an inconvenience for travel as visibility is reduced. When it’s hazy in different parts of the solar system, the impact is much more significant.
Haze comprises solid particles suspended in gas, and it alters the way light interacts with that gas. Different levels and kinds of haze can affect how the particles spread out through the atmosphere, changing what scientists detect with their telescopes. Distorted observations can lead to miscalculations of the amounts of important substances in the air, such as water and methane, and the type and levels of particles in the atmosphere. Such misinterpretations can impair scientists’ conclusions about global temperatures, the thickness of an atmosphere, and other planetary conditions.
“Water is the first thing we look for when we’re trying to see if a planet is habitable, and there are already exciting observations of water in exoplanet atmospheres. But our experiments and modeling suggest these planets most likely also contain haze,” said Chao He, a planetary scientist at Johns Hopkins. “This haze really complicates our observations, as it clouds our view of an exoplanet’s atmospheric chemistry and molecular features.”
To counteract this, He and team have—for the first time—successfully simulated conditions in the laboratory that allow hazy skies to form in water-rich exoplanets. The new research is a crucial step in determining how haziness muddles observations by ground and space telescopes.
For their study, published in Nature Astronomy, the Johns Hopkins team developed two gas mixtures containing water vapor and other compounds hypothesized to be common in exoplanets. They beamed those concoctions with ultraviolet light to simulate how light from a star would start the chemical reactions that produce haze particles. They then measured how much light the particles absorbed and reflected to understand how they would interact with light in the atmosphere.
The new data matched the chemical signatures of a well-studied exoplanet named GJ 1214 b more accurately than previous research, demonstrating that hazes with different optical properties can lead to misinterpretations of a planet’s atmosphere.
The scientists ran the experiments in a custom-designed chamber in the laboratory of Sarah Hörst, a Johns Hopkins associate professor of Earth and planetary sciences.
“The big picture is whether there is life outside the solar system, but trying to answer that kind of question requires really detailed modeling of all different types, specifically in planets with lots of water,” said study co-author Hörst. “This has been a huge challenge because we just don't have the lab work to do that, so we are trying to use these new lab techniques to get more out of the data that we’re taking in with all these big fancy telescopes.”
Indeed, the Johns Hopkins team is the first to determine how much haze can form in water planets beyond the solar system.
The scientists are now working to create more lab-made haze “analogs” with gas mixtures that more accurately represent what they see with telescopes.
“People will be able to use that data when they model those atmospheres to try to understand things like what the temperature is like in the atmosphere and the surface of that planet, whether there are clouds, how high they are and what they are made of, or how fast the winds go,” Hörst said. “All those kinds of things can help us really focus our attention on specific planets and make our experiments unique instead of just running generalized tests when trying to understand the big picture.”