Scientists have detected the first liquid waves on the surface of another world after they found telltale signs of isolated rippling in a sea on Saturn's moon Titan.
The signature of isolated ripples was observed in the 380-km wide sea on Titan called Punga Mare.
Unlike Earth's waves of water, the seas on Titan are composed of hydrocarbons such as ethane and methane. These exist in their liquid state on Titan, where the surface temperature averages about -180C.
The new findings were discussed by planetary scientist Jason Barnes, of the University of Idaho in US, at the 45th Lunar and Planetary Science Conference (LPSC), which was held in Texas.
Titan is a bizarre, looking-glass version of Earth with a substantial atmosphere and a seasonal cycle. Wind and rain shape the surface to form river channels, seas, dunes and shorelines.
The vast majority of Titan's lakes and seas are concentrated around the north polar region. Just one of these bodies of liquid - Ligeia Mare - is estimated to contain about 9,000 cubic km of mostly liquid methane, equating to about 40 times the proven reserves of oil and gas on Earth.
An image of Titan's north pole taken by the Cassini probe during a flyby in July 2012 shows sunlight being reflected from surface liquid in much the same way as a mirror re-directs light. This phenomenon is known as a specular reflection, 'BBC News' reported.
Barnes used a mathematical model to investigate whether the features in the image were compatible with waves.
"We think we've found the first waves outside the Earth," he said.
"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.
Barnes said other possibilities, such as a wet mudflat, could not be ruled out.
However, assuming these were indeed waves, Barnes calculated 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, Barnes said.
As Titan's seasons change, the wind speeds are expected to increase, which will cause bigger waves to form. If the increased wind creates waves, Cassini should have the ability to detect and capture them through imaging.
