Researchers may have finally confirmed the existence of liquid waves on Saturn's moon Titan, a phenomenon scientists have spent years searching for without success.
Scientists have long been interested in Titan because of its seemingly terrestrial properties. NASA describes the moon as "one of the most Earth-like worlds we have found to date. With its thick atmosphere and organic-rich chemistry, Titan resembles a frozen version of Earth, several billion years ago, before life began pumping oxygen into our atmosphere." So the possibility of waves, a feature unique to Earth in our solar system, on the surface of Titan has long intrigued researchers. Finally, they may have some proof to back up the scientific speculation.
According to planetary scientist Jason Barnes, unusual reflections off the surface of one of the moon's hydrocarbon seas, Punga Mare, could have been caused by ripples across the lunar ocean's surface. Punga Mare is made up of gases like methane and ethane, which exist in their liquid forms on Titan's -180 Celsius surface. Barnes examined images captured by NASA's Cassini mission in 2012 and 2013 and presented his findings at this year's Lunar and Planetary Science Conference, currently underway in Texas.
Barnes said that in some images, certain pixels are brighter than they would be if caused by reflecting sunlight. So he thought that these show a disturbance in the surface, like waves. The BBC explains that Barnes developed mathematical models to help determine whether the images could plausibly represent tiny waves:
"We think we've found the first waves outside the Earth," [Barnes] told the meeting. "What we're seeing seems to be consistent with waves at just a few locations in Punga Mare [with a slope] of six degrees." He said other possibilities, such as a wet mudflat, could not be ruled out. But assuming these were indeed waves, Dr Barnes calculates that a wind speed of around 0.75 m/s is required to produce ripples with the requisite slope of six degrees. That points to the waves being just 2cm high. "Don't make your surfing vacation reservations for Titan just yet," Dr Barnes quipped.
Physicist Ralph Lorenz told the BBC that as seasons change on Titan, stronger winds could mean larger waves. "The expectation is that any day now, the winds will start getting strong enough as we move into northern summer, and the waves will start picking up," he said. It takes Titan around 29 earth years to circle the sun.
According to Nature's Alexandra Witze, other researchers also concluded that Cassini may have spotted waves on Titan's surface:
Last summer, Cassini scientists spotted what they called a ‘magic island’ in another sea, Ligeia Mare, that appeared and then disappeared. It looked like a bright reflection in one image but was not visible 16 days later or in any photographs taken since, said Jason Hofgartner, a planetary scientist at Cornell University in Ithaca, New York. After ruling out possibilities such as an island exposed by a change in sea level, the team concluded that the ‘magic island’ is probably a set of waves, a group of bubbles rising from below the surface or a suspended mass, such as an iceberg.
But neither of these reports offer conclusive evidence of waves on Titan. It's possible that the pixels Barnes identified as unusual were simply representations of sunlight reflecting off a wet, solid surface. If this is the case, the second report would, so to speak, hold less water. For the record, scientists don't expect to find alien life on Titan. (But everyone can keep dreaming.)