Astronomers atop Maunakea detect cloud convection near Titan’s lakes

Astronomers using W. M. Keck Observatory on Maunakea, Hawaiʻi Island have found the first evidence of methane cloud convection in the northern hemisphere of Saturn’s moon Titan. The moon is of high astrobiological interest due to its complex organic (carbon-containing) chemistry.

Using Keck Observatory’s high-resolution imaging and adaptive optics, researchers observed methane clouds forming and shifting near Titan’s north pole—home to most of the moon’s lakes and seas. The study, led by NASA Goddard Space Flight Center scientist Conor Nixon, was published this week in Nature Astronomy.

“With Keck Observatory’s excellent imaging capability, we were able to see methane clouds evolving and changing close to Titan’s north pole over multiple days,” Nixon said. “This enables us to better understand Titan’s climate cycle, how the methane clouds may generate rain and replenish methane evaporated from the lakes.”

The team observed Titan in November 2022 and again in July 2023 using both Keck and NASA’s James Webb Space Telescope. Over several days, they tracked clouds rising in altitude, similar to convective cells on Earth.

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.

Although they were not able to directly see any precipitation occurring, the science team observed clouds that appeared to move to higher altitudes over a period of day.

It was the first time such cloud convection had been observed in Titan’s northern hemisphere. Previous studies have recorded similar activity in the south, but this recent discovery is significant because Titan’s northern region contains most of its surface methane lakes, which are comparable in area to North America’s Great Lakes.

“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,” Nixon said.

Webb’s data also provided a key missing piece for the 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.

Research shows that methane loss over time could dramatically reshape Titan. Unless the methane is resupplied—possibly from beneath the surface—Titan may eventually lose its atmosphere and become an “airless world of dust and dunes,” Nixon said.

The team plans to continue monitoring Titan’s weather, especially after the moon’s equinox in May 2025, when dramatic seasonal changes are expected.

The Twilight Zone program at Keck Observatory was key in enabling Nixon and his team to monitor how the weather on Titan changes over time. This program is run jointly by several University of California, California Institute of Technology and NASA researchers in collaboration with the Keck Observatory to observe several bright targets during periods when the sky is too bright for standard astronomical observations.