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Calm down, it’s not a second Earth. It’s a giant gas planet, the size of Saturn, and the so-called mild temperature still exceeds 70 degrees. But it’s the first time that the atmosphere of a temperate giant planet has been read, and what appeared inside was methane gas.
The planet is called TOI-199b, it is more than 330 light-years from Earth and is a gas giant the size of Saturn. The discovery was published in a study on May 20, 2026, in the scientific journal The Astronomical Journal.
According to Pennsylvania State University, Penn State, which led the research along with NASA’s Jet Propulsion Laboratory, JPL, the James Webb telescope read the atmosphere of the exoplanet and found it full of methane, with traces of ammonia and carbon dioxide. The information was released on May 21, 2026.
Why “temperature similar to Earth’s” doesn’t mean a new home
TOI-199b is a giant ball of gas, with no ground to stand on, similar to Saturn, which orbits its star every 105 days. The estimated temperature is around 79 degrees Celsius, hot by our standards, but surprisingly mild compared to what is usually seen in giant planets.
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This is where “similar to Earth’s” comes in. The comparison is not with our climate, but with other giants. The so-called hot Jupiters, which orbit very close to their stars, exceed a thousand degrees. Meanwhile, the giants of our solar system, like Jupiter and Saturn, are hundreds of degrees below zero. TOI-199b is in the middle, hence the nickname temperate. A temperature similar to Earth’s, in this context, means merely away from extremes, not a habitable world.
What makes this planet so rare
The charm of the story is its rarity. Almost every giant planet that astronomers can study up close is one of those hot Jupiters, easy to observe because they are enormous and scorching. Cold giants, like ours, are distant and icy. A temperate giant, just right, is a rare collectible piece.
TOI-199b is one of the very few known temperate giant exoplanets, and the first to have its atmosphere studied in detail. For astronomy, it’s like opening a door that was closed: an entire class of worlds that no one had managed to peek inside until now.
How the James Webb read a planet 330 light-years away
It may seem like magic to read the air of a planet so far away, but the technique has a name and logic. It’s called transmission spectroscopy. When the planet passes in front of the star, some of its light passes through the planet’s atmosphere before reaching us. The James Webb telescope separates this light into its various colors, like a prism does with white light, and each gas leaves a sort of fingerprint there.
That’s how the team found methane. This gas is common in the icy giants of our solar system, but it was notably missing in the middle ground of temperate planets. Finding a methane atmosphere in this type of world fills a gap that bothered scientists. The reading also brought clues of other gases, and new observations should reveal how much of each exists in this methane atmosphere.
Why this matters, even for Earth
In the end, the discovery is less about the planet itself and more about what it teaches. Each exoplanet of this type helps refine models of how planets and atmospheres are born and change over time. And, incredibly, understanding the chemistry of a temperate giant 330 light-years away can even provide clues about Earth’s own atmosphere.
Here’s a fun fact: the first exoplanet in history was discovered in 1992 by a team that included a researcher from the same Penn State. Since then, thousands of worlds have been cataloged, but only now has a temperate giant finally had its air read. The James Webb telescope didn’t find a new address for humanity; it found a new window to understand what worlds out there, and ours too, are made of.
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