New Model Could Help Astronomers Find Habitable Exoplanets

Artist's impression of a star illuminating the atmosphere of an exoplanet. NASA Goddard Space Flight Center

The hunt for habitable exoplanets has just gotten a new tool. Researchers from NASA's Goddard Institute for Space Studies have made a computer model that can help identify which exoplanets could potentially support life.

Astronomers used near-infrared telescopes to look for water vapor in a distant planet atmosphere. As far as we know, water is crucial for life and a planet should be able to host oceans for billions of years. We can’t detect these oceans directly but instruments could spot hints of the water cycle. The issue is that just spotting water in the upper atmosphere doesn’t mean it’s all good.

In their study published in the Astrophysical Journal, the team looked at how the amount of water in the atmosphere would change depending on the amount of light available to an exoplanet, as well as its interactions with its stars. The model is three-dimensional providing incredibly realistic outputs that astronomers hope to compare to real observations.

"Using a model that more realistically simulates atmospheric conditions, we discovered a new process that controls the habitability of exoplanets and will guide us in identifying candidates for further study," said lead author Yuka Fujii in a statement.

The crucial quantity in the study is water vapor mixing ratio. Depending on the amount of light the planet receives, this quantity might change and could reach a point at which most water has evaporated and the planet is nothing but a cloud world in a moist greenhouse state. The atmospheric circulation strongly depends on the star, something that wasn’t exactly clear based on previous one-dimensional models.

"As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state," added Anthony Del Genio, a co-author of the paper. "Current technology will be pushed to the limit to detect small amounts of water vapor in an exoplanet's atmosphere. If there is enough water to be detected, it probably means that planet is in the moist greenhouse state."

Newer and more powerful telescopes will come online in the next few years to help us discover more exoplanets and information about the objects we already know. Models like this will allow astronomers to allocate limited observation time to the planets that look likely to be habitable.

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