Two new "magic islands" have joined one reported last year on Saturn's giant moon Titan, Cassini spacecraft observations showed on Monday. The features add to a puzzling vanishing act playing out on the frozen world's seas.
Since Cassini first arrived at Saturn in 2004, its photos of Titan have revealed numerous seas, lakes, and rivers on the giant moon's frozen surface. This summer, images showed a mysterious feature in one sea—the first "magic island"—that appeared glinting on a lake's surface and then quickly vanished. (Related: "Waves Discovered on Saturn's Moon, Titan?")
The find raised speculation that scientists had captured views of waves splashing within the otherwise mirror-smooth liquid methane seas on the moon. Or else it was a fluke.
Now, an August 21 flyby has turned up two more strange reflecting features, magic islands that weren't there in earlier flybys. "They just popped up," says Cornell's Alexander Hayes, who presented the latest survey of Titan's seas at a briefing at the American Astronomical Society's Division for Planetary Sciences meeting.
A false-colour mosaic from space shows the northern seas beneath the haze of Titan.
PHOTOGRAPH BY NASA/JPL-CALTECH/UNIVERSITY OF ARIZONA/UNIVERSITY OF IDAHO
"They could be waves, or they could be something more solid," says MIT's Jason Soderblom, a member of the Cassini team reporting the observations. "We definitely know now they are something reflecting from the surface."
Since Titan is the only body besides Earth that has rain-carved geography to study, the possibility of a lake with waves intrigued scientists enough to keep them looking.
"After ten years there, Titan still can surprise us," Hayes says. "Titan has dunes, lakes, seas, even rivers. All this makes Titan an explorer's utopia."
An August 21 flyby passing some 599 miles (964 kilometres) above Titan allowed Cassini to investigate the depth of Kraken Mare, the largest sea on the frozen moon. Radar observations from the spacecraft covered a 120-mile (200-kilometre) shore-to-shore strip of the methane sea.
That flyby revealed that Kraken Mare reaches more than 656 feet (200 metres) deep. That's a lot of methane; the next largest sea on Titan, Ligeia Mare, holds three times the volume of Lake Superior.
Though Earth and Titan are the only known worlds in the solar system with seas and lakes, the ones on Titan are quite different from Earth's. Surface temperatures on the moon are around -290°F (-179°C), and its lakes are filled with liquid methane, ethane, and other liquefied natural gases.
Only in the past year did Italian planetary scientist Marco Mastrogiuseppe of the Sapienza University of Rome show Cassini scientists how to measure the depths of the moon's lakes. The technique led Cassini's managers at NASA's Jet Propulsion Laboratory to change their way of looking at seas on the moon, and resulted in the August flyover.
The August flyby included not only radar, but also spectrometer observations that definitively ruled out the magic islands being some sort of sub-sea iceberg or fog atop the liquid inadvertently detected by the spacecraft, Soderblom says.
With spring returning to the northern hemisphere of Titan, where Kraken Mare resides, the scientists suspect they will soon see more mysteries disturbing the once placid surface of the seas of Titan.
"We are likely to see more islands showing up," Hayes says. "These lakes and seas are dynamic places."
Header Image: A Cassini flyby of Titan viewed a narrow stretch of the moon's Kraken Mare sea. PHOTOGRAPH BY NASA/JPL-CALTECH/ASI/CORNELL