Scientists Perform First Lab Simulation Of An Exoplanet’s Atmospheric Haze

Artist's impression of what a hazy Earth might have looked like. NASA’s Goddard Space Flight Center/Francis Reddy

Researchers from Johns Hopkins University have now looked into haze formation for a simulated exoplanet atmosphere – a first in the field of exoplanetary studies. The scientists hope it will help us understand the impact that haze might have on the possibility of life on planets outside our Solar System. The results of the experiment are reported in Nature Astronomy.

Current telescopes sometimes struggle to fully characterize exoplanetary atmospheres because of the haze, which consists of solid particles suspended in the gas. The haze is a product of chemical reactions due to the light from the parent stars. By using different gas mixtures and recreating similar conditions, they were able to simulate these hazy atmospheres.

“One of the reasons why we’re starting to do this work is to understand if having a haze layer on these planets would make them more or less habitable,” lead author Professor Sarah Hörst said in a statement. “The fundamental question for this paper was: Which of these gas mixtures – which of these atmospheres – will we expect to be hazy?”

The researchers looked at super-Earths (rocky planets bigger than our own) and mini-Neptunes (smaller gas giants). They changed the mixture of three main gases (carbon dioxide, hydrogen, and water vapor) with four other gases (helium, carbon monoxide, methane, and nitrogen) and used three sets of temperatures. This allowed them to create nine different model atmospheres.

“The energy breaks up the gas molecules that we start with," Hörst explained. "They react with each other and make new things and sometimes they’ll make a solid particle [creating haze] and sometimes they won’t."

Each variant made haze in different ways and they were surprised by some of the results. The team expected the presence of methane to produce a lot of haze, like on Saturn’s moon Titan, but it was actually water-rich atmospheres that were the most prolific haze producers. This might have important implications for life, as the haze changes the temperature profile of atmospheres and can even shield surfaces from the most powerful photons.

“The production rates were the very, very first step of what’s going to be a long process in trying to figure out which atmospheres are hazy and what the impact of the haze particles is,” Hörst concluded.

The team plans to continue investigating the different hazes to understand how light interacts with the different types of atmospheres, as well as to produce new ones by changing the composition, temperature, and energy sources.

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