Saturn’s moon Titan is an intriguing world cloaked in a yellowish, smoggy haze. Similar to Earth, the atmosphere is mostly nitrogen and has weather,
Saturn’s moon 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, with a weather driven by evaporating and condensing water, frigid Titan has a methane cycle, reported NASA.
NASA’s James Webb Space Telescope, supplemented with images from the Keck II telescope, has for the first time found evidence for cloud convection in Titan’s northern hemisphere, over a region of lakes and seas. Webb also has detected a key carbon-containing molecule that gives insight into the chemical processes in Titan’s complex atmosphere.
On Titan, methane plays a similar role to water on Earth when it comes to weather. 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, reported NASA.
“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,” explained lead author Conor Nixon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
The team observed Titan in November 2022 and July 2023 using both Webb and one of the twin ground-based W.M. Keck Observatories telescopes. 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. Their total area is similar to that of the Great Lakes in North America, reported NASA.
On Earth the lowest layer of the atmosphere, or troposphere, extends up to an altitude of about 7 miles (12 kilometers). However, on Titan, the lower gravity allows the atmospheric layers to expand, the troposphere extends up to about 27 miles (45 kilometers). Webb and Keck used different infrared filters to probe to different depths in Titan’s atmosphere, allowing astronomers to estimate the altitudes of the clouds. The science team 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.
Titan is an object of high astrobiological interest due to its complex organic (carbon-containing) chemistry. 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, reported NASA.
The basic ingredient that drives much of Titan’s chemistry is methane, or CH4. 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 (C2H6) along with more complex carbon-bearing molecules.
Webb’s data provided a key missing piece for our understanding of the chemical processes: a definitive detection of the methyl radical CH3. This molecule (called “radical” because it has a “free” electron that is not in a chemical bond) 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, reported NASA.
“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 co-author Stefanie Milam of the 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, reported NASA.
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. 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,” said Nixon, as reported by NASA.
More of Titan’s mysteries will be probed by NASA’s Dragonfly mission, a robotic rotorcraft scheduled to land on Saturn’s moon in 2034. Making multiple flights, Dragonfly will explore a variety of locations. Its in-depth investigations will complement Webb’s global perspective.
“By combining all of these resources, including Webb, NASA’s Hubble Space Telescope, and ground-based observatories, we maintain continuity between the former Cassini/Huygens mission to Saturn and the upcoming Dragonfly mission,” added Heidi Hammel, vice president of the Association of Universities for Research in Astronomy and a Webb Interdisciplinary Scientist, as reported by NASA.
All Credit To: NASA, ESA, CSA
COMMENTS