Titan, the largest moon of Saturn, is the only moon in the Solar System with a dense atmosphere, and it is also the only planetary body other than Earth that currently has rivers, lakes, and seas.
These images of Saturn’s moon Titan were captured by Webb’s NIRCam instrument on November 4, 2022. Left: image using F212N, a 2.12-micron filter sensitive to Titan’s lower atmosphere; the bright spots are prominent clouds in the northern hemisphere. Right: color composite image using a combination of NIRCam filters; several prominent surface features are labeled: Kraken Mare is thought to be a methane sea; Belet is composed of dark-colored sand dunes; Adiri is a bright albedo feature. Image credit: NASA / ESA / CSA / A. Pagan, STScI / Webb Titan GTO Team.
Titan is a carbon-rich, oxygen-poor world with a wide range of organic and inorganic compounds, atmospheric energy sources, and liquid hydrocarbon seas and lakes.
It is the only planetary body in the Solar System, except our planet, where rainfall and seasonally flowing liquids erode the landscape.
In addition to a hazy mixture of nitrogen and hydrocarbons like methane and ethane, the atmosphere of this strangely Earth-like world also contains an array of more complex organic molecules.
Planetary scientists think that this chemical make-up is similar to Earth’s primordial atmosphere.
“We had waited for years to use Webb’s infrared vision to study Titan’s atmosphere, including its fascinating weather patterns and gaseous composition, and also see through the haze to study albedo features — bright and dark patches — on the surface,” Dr. Conor Nixon, a planetary scientist at the NASA Goddard Space Flight Center, and his colleagues said in a statement.
“Titan’s atmosphere is incredibly interesting, not only due to its methane clouds and storms, but also because of what it can tell us about Titan’s past and future — including whether it always had an atmosphere. We were absolutely delighted with the initial results.”
Evolution of clouds on Titan over 30 hours between November 4 and 6, 2022, as seen by Webb’s NIRCam (left) and Keck’s NIRC-2 (right) instruments. Titan’s trailing hemisphere seen here is rotating from left (dawn) to right (evening) as seen from Earth and the Sun. Cloud A appears to be rotating into view while Cloud B appears to be either dissipating or moving behind Titan’s limb (around toward the hemisphere facing away from us). Clouds are not long-lasting on Titan or Earth, so those seen on November 4 may not be the same as those seen on November 6. Image credit: NASA / ESA / CSA / A. Pagan, STScI / Webb Titan GTO Team.
Using images from Webb’s Near-Infrared Camera (NIRCam), the researchers detected several clouds in Titan’s atmosphere.
“By comparing different Webb/NIRCam images, we soon confirmed that a bright spot visible in Titan’s northern hemisphere was in fact a large cloud. Not long after, we noticed a second cloud,” they said.
“Detecting clouds is exciting because it validates long-held predictions from computer models about Titan’s climate, that clouds would form readily in the mid-northern hemisphere during its late summertime when the surface is warmed by the Sun.”
“We then realized it was important to find out if the clouds were moving or changing shape, which might reveal information about the air flow in Titan’s atmosphere.”
“So we quickly reached out to colleagues to request follow-up observations using Keck Observatory in Hawai’i.”
“We were concerned that the clouds would be gone when we looked at Titan two days later with Keck, but to our delight there were clouds at the same positions, looking like they had changed in shape,” said Dr. Imke de Pater, an astronomer with the University of California, Berkeley, who has extensive experience using Keck.
The scientists also collected spectra of Titan with Webb’s Near-Infrared Spectrograph (NIRSpec), which is giving us access to many wavelengths that are blocked to ground-based telescopes like Keck by Earth’s atmosphere.
“These data, which we are still analyzing, will enable us to really probe the composition of Titan’s lower atmosphere and surface in ways that even NASA’s Cassini spacecraft could not, and to learn more about what is causing the bright feature seen over the south pole,” they said.
