NASA’s James Webb Space Telescope and the Keck II telescope have found evidence of cloud convection in the northern hemisphere of Titan, Saturn’s largest moon. The images in July 2023 show methane clouds at different altitudes in this region, where most of Titan’s lakes and seas are located. Titan is the only place in our solar system besides Earth with weather, clouds, and rainfall.
However, Titan’s weather is driven by a methane cycle, unlike Earth’s water cycle. Methane evaporates from the surface, rises into the atmosphere, condenses to form clouds, and occasionally falls as a chilly, oily rain onto a solid surface where water ice is as hard as rocks. Dr. Conor Nixon, an astronomer at NASA’s Goddard Space Flight Center, and his colleagues observed Titan in November 2022 and July 2023. They saw clouds in the mid and high northern latitudes during Titan’s summer, and these clouds appeared to rise to higher altitudes over time. This is the first time evidence for cloud convection has been seen in Titan’s northern hemisphere.
This is significant because most of Titan’s lakes and seas are located there, and evaporation from these lakes is a major source of methane. Titan’s lower gravity allows the atmospheric layers to expand, extending the troposphere up to about 45 km, compared to Earth’s 12 km. Webb and Keck used different infrared filters to probe different depths in Titan’s atmosphere, allowing astronomers to estimate cloud altitudes.
They observed clouds that moved to higher altitudes over days, although no precipitation was directly observed.
Webb telescope documents Titan’s clouds
Dr. Thomas Cornet, a researcher with ESA, noted that Webb’s observations were taken at the end of Titan’s northern summer, a season not observed by the Cassini-Huygens mission. With ground-based observations, Webb is providing new insights into Titan’s atmosphere that scientists hope to investigate closely in the future with a possible ESA mission to the Saturn system. Titan is of high astrobiological interest due to its complex organic chemistry, despite its frigid temperature of minus 180 degrees Celsius.
Organic molecules form the basis of life on Earth, and studying them on Titan may help scientists understand the processes that led to life on Earth. The Webb data also provided a key missing piece for understanding Titan’s chemical processes: the definitive detection of the methyl radical (CH₃), which forms when methane is broken apart. This means scientists can now observe chemical processes in action on Titan, instead of just starting ingredients and final products.
Titan’s hydrocarbon chemistry has long-term implications. Methane will deplete over time unless it is resupplied, as some hydrogen escapes from the atmosphere when methane breaks apart in the upper atmosphere. A similar process on Mars led to its dry, desert conditions due to the loss of water-derived hydrogen.
Dr. Nixon noted that methane is a consumable on Titan and may be constantly resupplied from the crust and interior over billions of years. If not, eventually, Titan will become a mostly airless world of dust and dunes.
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