Scientists at Goddard Space Flight Center have tapped the James Webb Telescope (JWST) to study Titan. It was able to detect for the first time evidence of cloud convection in the Northern Hemisphere of the moon over a region of lakes and seas. JWST also discovered a key carbon-containing molecule that provides insight into chemical processes in Titan’s atmosphere.
Weather on Titan
Titan is the only place in the Solar System where the weather is similar to Earth’s, in the sense that it has clouds and rain on the surface. Only while water plays a key role on our planet, the cornerstone of Titan’s weather cycles is methane. It evaporates from the surface and rises into the atmosphere where it condenses to form methane clouds. Sometimes it then falls as rain to the surface, where the water ice plays the role of hard rock.
Between 2022 and 2023, a team of researchers from NASA conducted a series of observations of Titan involving JWST and one of the Keck Observatory’s twin ground-based telescopes. They have shown not only the presence of clouds in Titan’s mid to high northern latitudes, where it is summer, but also found that they rise to higher altitudes over time. This is important because most of Titan’s lakes and seas are located in its Northern Hemisphere, and evaporation from the moon’s hydrocarbon reservoirs is a major potential source of methane.
On Earth, the lowest layer of the atmosphere (the troposphere) extends to a height of about 12 km. However, on Titan, where lower gravity allows atmospheric layers to expand, the troposphere extends to about the 45 km mark. The infrared observations allowed astronomers to estimate cloud heights and track cloud movements, although they were not able to see the precipitation directly.
Titan’s complex atmospheric chemistry
Titanium is of great astrobiological interest due to its complex carbon-containing chemical composition. Organic molecules form the basis of all life on Earth. Studying them on a world like Titan can help scientists understand the processes that led to the origin of life on our planet.
The main component that defines much of Titan’s chemistry is methane. It is split by sunlight or energetic electrons from Saturn’s magnetosphere and then recombines with other molecules to form substances such as ethane and more complex carbon-containing molecules.
Webb’s data revealed a key missing fragment for understanding chemical processes: methyl (CH3). This molecule, called a “free radical” (because it has a “free” electron that is not part of a chemical bond), is formed when methane is broken down. The discovery of this substance means that scientists will be able to see Titan’s atmospheric chemical processes in action for the first time, not just their initial ingredients and end products.
Future of Titan’s atmosphere
This hydrocarbon chemistry has long-term implications for Titan’s future. When methane decays in the upper atmosphere, some of it recombines to form other molecules that end up back at the surface in some chemical form, and some of the hydrogen escapes from the atmosphere.
A similar process once occurred on Mars, where water molecules broke down and the resulting hydrogen escaped into space. The result was the dry, desolate planet we see today. This means that unless Titan has some permanent source to replenish methane, its supply may be depleted in the future. When it disappears, the moon will turn into an atmosphere-free world of dust and dunes, somewhat reminiscent of Mars.
Earlier we reported on how scientists estimated the biomass potential of Titan’s hypothetical subsurface ocean.
According to NASA
