Earth isn't the only world in the solar system with active lakes, rivers, and oceans.
About 880 million miles away in space, Saturn's largest moon Titan is also flush with surface liquid that evaporates, forms clouds in its hazy atmosphere, and rains. Despite this seemingly similar hydrology, the two planetary bodies couldn't be more different: Titan's oceans are made of methane and ethane — not water. Though people tend to think of those chemicals as gasses, they act like liquids on this super-cold moon, like gasoline on Earth.
Despite NASA's Cassini spacecraft mapping more than 620,000 square miles of lakes and oceans on Titan before the end of its mission in 2017, much of how these alien seas behave remains a mystery. But a new study published in Science Advances suggests that these liquids may indeed ripple, surge, and swell against Titan's shorelines, just as water does on Earth.
Whether Titan's oceans are still or have waves has been debated for more than 15 years, said Rose Palermo, a geologist and lead author of the study.
"Some people who tried to see evidence for waves didn't see any, and said, 'These seas are mirror-smooth,'" Palermo said in a statement. "Others said they did see some roughness on the liquid surface but weren't sure if waves caused it."
Using computer models to simulate different erosion mechanisms that occur on Earth, a team mostly composed of MIT geologists found that waves were the likely source of erosion to have formed the coastal shapes seen in Cassini's radar images.
If Titan's oceans exhibit waves, that could give scientists insight into the moon's climate. They could then begin predicting the strength of wind on this world and infer what direction it's often blowing — factors that might be necessary to power such waves.
"If we could stand at the edge of one of Titan's seas," said coauthor Taylor Perron, in a statement, "we might see waves of liquid methane and ethane lapping on the shore and crashing on the coasts during storms."
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In order to prove beyond a shadow of doubt that Titan's liquids are moving in waves, scientists will eventually need direct views of this activity. That may be possible in the next decade, when NASA's Dragonfly, a helicopter-like robotic spacecraft, arrives at the moon for exploration in 2034. The $3.35 billion mission is slated to launch in 2028.
NASA has made the mission a priority because Titan's icy dunes appear to have the organic ingredients for life — the kinds that we know about, at least — to potentially emerge.
