Found: A Saturn with almost Earth-like temperatures
One of the really fun things about planetary science is dreaming up “what ifs” that explore all the science fiction possibilities with real science.
But predicting what’s possible isn’t nearly as cool as seeing what’s real, and thanks to JWST we can now see real worlds with real atmospheres orbiting other stars.
A new paper in the Astronomical Journal, led by Aaron Bello-Arufe (JPL), highlights JWST’s observations of the Saturn-sized world TOI199b. Discovered in 2023 from TESS mission data, TOI-199b orbits a Sun smaller and cooler than our Sun, on an orbit half the size of Earth’s orbit. While the Penn State press release calls the world’s 175 degree F / or 80 degree C temperatures Earth-like, we’re going to go with almost Earth-like since most Earth life would be quite dead at this temperature.
While deadly hot, this world is friendlier compared to the air freezing or water boiling temperatures found on the majority of worlds we see across the galaxy. As team leader Renyu Hu (Penn State) points out, “Astronomers have found thousands of exoplanets. But only a few giant, temperate exoplanets are known and this is the first time that we have been able to study the atmosphere of one of them in detail.”
This project wasn’t as easy as pointing JWST and getting a spectrum of the world. The team had to observe the star for 20 hours to get a complete understanding of its light and variations. They then watched the planet pass in front of the star and gathered data for the 7 hours it took the planet to transit and carefully subtracted the Star’s light from the Star+Planets light to get the planets light.
I lack sufficient words to explain how amazing it was for them to get more than a day of JWST observing time to study one world. This project was a risk, but it was a risk that paid off!
JWST revealed TOI-199b’s atmosphere was rich in Methane with hints of ammonia and carbon dioxide. Nicely, this is consistent with predictions! With this success, the research team will now look to get time to observe even more worlds and their atmospheres.
Sources
- PennState Press Release
- Bello-Arufe, Aaron, et al. “Methane on the Temperate Exo-Saturn TOI-199 b.” The Astronomical Journal 171.6 (2026): 354. DOI: 10.3847/1538–3881/ae4fba
