Sonntag, 6. März 2016 - 21:45 Uhr
This image shows the evolution of a transient feature in the large hydrocarbon sea named Ligeia Mare.
By comparing radar images of Saturn's exotic moon Titan, scientists have found a bright, island-like feature that has changed over time. The images, captured by the Cassini spacecraft from 2007 through 2015, show this "magic island" brightening and then dimming again.
From studying the images, scientists conclude the brightening is most likely due to waves at or beneath the surface. They do not think it's likely to be caused by tides or sea level or seafloor changes. The surface of Titan is extremely cold, on average about -180ºC, but methane and other hydrocarbons on its surface can still exist in liquid form. The "lake" shown in this image, Ligeia, is Titan's second-largest liquid hydrocarbon sea. With an area of about 130,000 square kilometers, it is nearly as large as the Caspian Sea, Earth's largest lake.
Previous images indicate other, similar features exist in Kraken Mare, Titan's largest hydrocarbon sea. With these observations, planetary scientists are beginning to understand that this moon's oceans are not stagnant, but are instead dynamic environments. Cassini will have one more opportunity to look for "magic island" in 2017, during its final, close flyby.
Until recently, it seemed unlikely NASA would visit Titan again any time soon. In the final 2016 federal budget, however, the US Congress created an Ocean Worlds exploration program. It directs NASA to begin designing missions to explore the cold, icy moons of the outer Solar System, including Europa, Titan, and another of Saturn's moons, Enceladus. These, and other worlds around Jupiter and beyond are thought to harbor liquid oceans in some form or another.
The director of NASA's Jet Propulsion Laboratory, Charles Elachi, testified at a hearing of the House Appropriations subcommittee regarding this Ocean Worlds program last Thursday. He noted that Titan is a totally new frontier for organic chemistry—a place where an entirely different kind of life might have evolved.
"Titan is a world full of organic molecules, which are of course key building blocks for life," Elachi said. "Clouds in Titan’s atmosphere rain out liquid methane and ethane, which then collects into lakes that dot Titan’s Earth-like landscape. On Earth, however, our lakes are carved into rock, whereas on Titan the lakes of methane and ethane are carved into a shell of water ice. Beneath Titan’s icy shell may reside a global liquid water ocean. Could life have arisen on such a world? For many in the planetary science community, Titan is heralded as the place to go to look for "weird life"—life unlike life as we know it, life that may have originated in liquid methane instead of liquid water."
Quelle: ars technica