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NASA's Cassini spacecraft used infrared cameras to map under the surface of Titan, Saturn's moon. (Credit: NASA / JPL-Caltech / University of Nantes / University of Arizona)
The age of exploration may have passed on Earth, but it's only just beginning on Titan, Saturn's largest moon. It is a world larger than the planet Mercury. NASA's Cassini spacecraft studied the moon (with Saturn and its other moons) for 13 years and even deployed a landing gear, Huygens, on Titan's surface. But although Cassini's mission ended in 2017, his data is still alive and planetary scientists continue to learn more about the history and surface features of this strange moon-like Earth.
The researchers spotted Titan's landscapes of surprising diversity, ranging from vast shots to sandy dunes to rivers and lakes. But as the world is so cold, these features consist of liquid methane and other organic compounds that slide on a rocky substrate of hard, solid ice. It is difficult to obtain superb observations of the surface, because the atmosphere of the moon is a dense haze.
But even if the clouds prevent getting good data, an article published this week in Nature Astronomy shows the utility of a new analysis technique for mapping Titan and understanding its subtle superficial characteristics. And, almost as a bonus, he also spotted a totally unexpected feature: a ribbon of ice exposed in the bedrock that wraps itself almost halfway around the moon.
A dust storm crosses Titan. (NASA / ESA / IPGP / Labex UnivEarthS / Paris Diderot University)
Easy PCA
The new technique is called Principal Component Analysis (PCA) and could change the rules of the game for Titan-ophiles. Instead of examining individual pixels in Cassini photos and browsing them for details and data, PCA examines all the pixels in a given area to identify landscape trends. This leads not only to more refined data, but also proves much less tedious than the main alternatives, which must go pixel by pixel.
To test their new tool and try to answer the question of why some rock plates in place are on display, the international team of researchers applied the APC on half of Titan's surface, between 30 ° S and 30 ° N. tropics in part because the data from this region were already relatively good, including first-hand of the Huygens lander. This facilitated verification of their results.
Once everything was correlated and deemed accurate, the team ended up with a high-definition water ice distribution on Titan. And curiously, the authors write, it's formed in a remarkable pattern. "Our PCA study indicates that water ice is unevenly, but not randomly, exposed on the tropical surface of Titan. Most of the ice-rich materials on display follow a long, almost linear corridor that extends 6,300 kilometers, or nearly 4,000 miles. That's about 40% of Titan's circumference. And, for reference, the United States spans less than 3,000 miles from coast to coast to coast.
The newly discovered 4,000 km long Titan Ice Corridor is outlined in blue through these three views of the moon's surface. (Credit: NASA / JPL-Caltech / Institute of Space Science)
Titan Exposed
The discovery is, in a word, strange. "This corridor is confusing because it does not correspond to the topography or measurements of the subsoil," write the authors. They also point out that the only other areas of Titan with a large amount of ice exposed in the bedrock are areas "dug by craters or exposed to erosion". this gigantic new feature of a foreign world.
Read more: Titan's ice canyons compete with those of Zion National Park
The team said it was possible that the frozen corridor had formed over the past billions of years, when Titan was still geologically active. And they wonder in particular if it is linked to a "major cryovolcanic event" – a glacial volcanism – which, according to astronomers, happened during this period. But to really answer this question, as well as the rest of Titan's mysteries, the authors say that further studies are needed.
Now that the APC has proved effective for this type of task, a new era of discoveries and responses could be envisioned for the largest moon of Saturn.
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