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Images of Saturn’s moon Titan, captured by the James Webb Space Telescope’s NIRCam instrument 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: Blue=F140M (1.40 microns), Green=F150W (1.50 microns), Red=F200W (1.99 microns), Brightness=F210M (2.09 microns). 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. Download the Titan NIRCam image from the Resource Gallery. Credit: NASA, ESA, CSA, A. Pagan (STScI). Science: JWST Titan GTO Team
On the morning of Saturday, November 5, an international team of planetary scientists woke up with great delight to the first Webb images of
Titan is larger than Earth’s moon, and even bigger than the planet Mercury. Titan is the only moon in our solar system that has clouds and a dense atmosphere. Apart from Earth, Titan is the only place in our solar system known to have liquids on its surface.
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. 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.
Team member Sebastien Rodriguez from the Universite Paris Cité was the first to see the new images, and alerted the rest of us via email: “What a wake-up this morning (Paris time)! Lots of alerts in my mailbox! I went directly to my computer and started at once to download the data. At first glance, it is simply extraordinary! I think we’re seeing a cloud!” Webb Solar System GTO Project Lead Heidi Hammel, from the Association of Universities for Research in Astronomy (AURA), had a similar reaction: “Fantastic! Love seeing the cloud and the obvious albedo markings. So looking forward to the spectra! Congrats, all!!! Thank you!”
Evolution of clouds on Titan over 30 hours between November 4 and November 6, 2022, as seen by Webb NIRCam (left) and Keck NIRC-2 (right). 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. The NIRCam image used the following filters: Blue=F140M (1.40 microns), Green=F150W (1.50 microns), Red=F200W (1.99 microns), Brightness=F210M (2.09 microns). The Keck NIRC-2 image used: Red=He1b (2.06 microns), Green=Kp (2.12 microns), Blue=H2 1-0 (2.13 microns). Credit: NASA, ESA, CSA, W. M. Keck Observatory. A. Pagan (STScI). Science: Webb Titan GTO Team
Thus began a day of frantic activity. By comparing different images captured by Webb’s Near-Infrared Camera (NIRCam), 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. 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 airflow in Titan’s atmosphere. So we quickly reached out to colleagues to request follow-up observations using the Keck Observatory in Hawai’i that evening. Our Webb Titan team lead Conor Nixon from
The team also collected spectra 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. This 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 the