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The James Webb Space Telescope has spied clouds on one of the solar system’s most intriguing moons.
In November, the space observatory turned its infrared gaze on Saturn’s largest moon, Titan. It’s the only moon in our solar system that has a dense atmosphere — four times denser than Earth’s.
Titan’s atmosphere is made of nitrogen and methane, which gives it a fuzzy, orange appearance. This thick haze obscures visible light from reflecting off the moon’s surface, making it difficult to discern features.
The Webb telescope observes the universe in infrared light, which is invisible to the human eye — on November 5, the telescope spotted a bright cloud in Titan’s northern hemisphere and, soon after, detected a second cloud in the atmosphere.
The larger cloud was located over Titan’s northern polar region near Kraken Mare, the largest known liquid sea of methane on the moon’s surface.
Titan has Earth-like liquid bodies on its surface, but its rivers, lakes and seas are made of liquid ethane and methane, which form clouds and cause rain from the sky. Researchers also believe Titan has an internal liquid water ocean.
“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,” cowrote Conor Nixon, a planetary scientist at the NASA Goddard Space Flight Center in Greenbelt, Maryland, on NASA’s Webb blog.
Nixon is also the principal investigator on the Webb observation program for Titan.
The team of astronomers studying the Webb observations reached out to colleagues at the W. M. Keck Observatory in Hawaii to see if follow-up observations could reveal if the clouds were moving or changing shape.
“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 Imke de Pater, emeritus professor of astronomy at the University of California, Berkeley, and lead of the Keck Titan Observing Team, in a statement.
Atmospheric modeling experts helped the team determine that the two telescopes had captured observations of seasonal weather patterns on Titan.
Webb’s Near-Infrared Spectrograph instrument was also able to collect data on Titan’s lower atmosphere, which can’t be seen by ground-based observatories such as Keck due to interference from Earth’s atmosphere, in different wavelengths of infrared light.
The data, which is still being analyzed, was able to see deeper into Titan’s atmosphere and surface than the Cassini spacecraft, which orbited Saturn and its moons for 13 years. Webb’s observations could also reveal the cause of a bright feature over Titan’s south pole.
The cloud observations were a long time coming.
“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 on the surface,” Nixon said, referring to the bright and dark patches.
“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.”
The team is planning more observations of Titan in June that may provide additional information about the gases in its atmosphere.