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Images of Saturn’s moon Moon, taken by the James Webb Space Telescope’s NIRCam instrument on November 4, 2022. Left: Image using F212N, a 2.12-micron filter sensitive to Titan’s lower atmosphere. Bright spots stand out from the 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), white=F210M (2.09 microns). Several surface eminences have been labeled: The Kraken Sea is thought to be a sea of methane; The belly is composed of sandy loam; Adiri is a white feature of albedo. Titan NIRCam image from 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 joy to the first Webb images.
data-gt-translate-attributes”[{” attribute=””>Saturn’s largest moon, Titan. Here, Principal Investigator Conor Nixon and others on the Guaranteed Time Observation (GTO) program 1251 team using Webb to investigate Titan’s atmosphere and climate describe their initial reactions to seeing the data.
Saturn’s largest moon Titan 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. Unlike Earth, however, the liquid on Titan’s surface is composed of hydrocarbons including methane and ethane, not water. Its atmosphere is filled with thick haze that obscures visible light reflecting off the surface.
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
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