Using data from the NASA/ESA/CSA James Webb Space Telescope and the Keck II telescope, asrtonomers found evidence of cloud convection in the northern hemisphere of Titan. Most of Titan’s lakes and seas are located in that hemisphere, and are likely replenished by an occasional rain of methane and ethane. Webb also has detected a key carbon-containing molecule that gives insight into the chemical processes in Titan’s complex atmosphere.
These images of Titan, taken by Webb on July 11, 2023 (top row), and the Keck II telescope on July 14, 2023 (bottom row), show methane clouds (white arrows) appearing at different altitudes in Titan’s northern hemisphere. Image credit: NASA / ESA / CSA / STScI / Keck Observatory.
Titan is an intriguing world cloaked in a yellowish, smoggy haze. Similar to Earth, the atmosphere is mostly nitrogen and has weather, including clouds and rain.
Unlike Earth, whose weather is driven by evaporating and condensing water, frigid Titan has a methane cycle.
It evaporates from the surface and rises into the atmosphere, where it condenses to form methane clouds.
Occasionally it falls as a chilly, oily rain onto a solid surface where water ice is hard as rocks.
“Titan is the only other place in our Solar System that has weather like Earth, in the sense that it has clouds and rainfall onto a surface,” said Dr. Conor Nixon, an astronomer at NASA’s Goddard Space Flight Center.
Using both Webb and the Keck II telescope, Dr. Nixon and colleagues observed Titan in November 2022 and July 2023.
Those observations not only showed clouds in the mid and high northern latitudes on Titan — the hemisphere where it is currently summer — but also showed those clouds apparently rising to higher altitudes over time.
While previous studies have observed cloud convection at southern latitudes, this is the first time evidence for such convection has been seen in the north.
This is significant because most of Titan’s lakes and seas are located in its northern hemisphere and evaporation from lakes is a major potential methane source.
On Earth the lowest layer of the atmosphere, or troposphere, extends up to an altitude of about 12 km.
However, on Titan, whose lower gravity allows the atmospheric layers to expand, the troposphere extends up to about 45 km.
Webb and Keck used different infrared filters to probe to different depths in Titan’s atmosphere, allowing the astronomers to estimate the altitudes of the clouds.
The researchers observed clouds that appeared to move to higher altitudes over a period of days, although they were not able to directly see any precipitation occurring.
“Webb’s observations were taken at the end of Titan’s northern summer, which is a season that we were unable to observe with the NASA/ESA Cassini-Huygens mission,” said Dr. Thomas Cornet, a researcher with ESA.
“Together with ground-based observations, Webb is giving us precious new insights into Titan’s atmosphere, that we hope to be able to investigate much closer-up in the future with a possible ESA mission to visit the Saturn system.”
Titan is an object of high astrobiological interest due to its complex organic (carbon-containing) chemistry, despite its frigid temperature of minus 180 degrees Celsius.
Organic molecules form the basis of all life on Earth, and studying them on a world like Titan may help scientists understand the processes that led to the origin of life on Earth.
The basic ingredient that drives much of Titan’s chemistry is methane.
Methane in Titan’s atmosphere gets split apart by sunlight or energetic electrons from Saturn’s magnetosphere, and then recombines with other molecules to make substances like ethane along with more complex carbon-bearing molecules.
The Webb data provided a key missing piece for our understanding of the chemical processes: a definitive detection of the methyl radical (CH3), which forms when methane is broken apart.
Detecting this substance means that scientists can see chemistry in action on Titan for the first time, rather than just the starting ingredients and the end products.
“For the first time we can see the chemical cake while it’s rising in the oven, instead of just the starting ingredients of flour and sugar, and then the final, iced cake,” said Dr. Stefanie Milam, a researcher at NASA’s Goddard Space Flight Center.
This hydrocarbon chemistry has long-term implications for the future of Titan.
When methane is broken apart in the upper atmosphere, some of it recombines to make other molecules that eventually end up on Titan’s surface in one chemical form or another, while some hydrogen escapes from the atmosphere.
As a result, methane will be depleted over time, unless there is some source to replenish it.
A similar process occurred on Mars, where water molecules were broken up and the resulting hydrogen lost to space. The result was the dry, desert planet we see today.
“On Titan, methane is a consumable,” Dr. Nixon said.
“It’s possible that it is being constantly resupplied and fizzing out of the crust and interior over billions of years.”
“If not, eventually it will all be gone and Titan will become a mostly airless world of dust and dunes.”
The results were published in the journal Nature Astronomy.
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C.A. Nixon et al. The atmosphere of Titan in late northern summer from JWST and Keck observations. Nat Astron, published online May 14, 2025; doi: 10.1038/s41550-025-02537-3
