Waves have been spotted on an alien world for the first time by Nasa scientists studying Titan, Saturn's largest moon.
The space agency's Cassini spacecraft noticed several abnormal glints of sunlight on the surface of one of the moon's hydrocarbon seas, Nature Magazine reports.
Researchers have been looking for waves rippling on Titan's oceans for years but to no avail, until recently.
Scientists at the University of Idaho in Moscow noticed tiny movements, not more than two centimetres, disturbing the surface of Punga Mare, one of Titan's oceans.
Findings were presented at the Lunar and Planetary Science Conference, where another research team also pointed to the possible presence of waves on Titan.
"Titan may be beginning to stir," said Ralph Lorenz, a planetary scientist from the Johns Hopkins University Applied Physics Laboratory. "Oceanography is no longer just an Earth science."
Scientists say they expect to see more waves over the next few years as winds pick up across the moon's northern hemisphere.
On the surface of Titan, liquid rains down then evaporates. Its oceans and lakes are formed of methane, ethane and other hydrocarbon compounds.
Despite having a complex weather system, however, waves have never been seen on the moon's surface before. Liquid hydrocarbons are more viscous than water and need stronger winds to move them than are present on the moon.
Researchers predicted Titan's winds would pick up as it moves into Spring – Saturn takes around 29 years to orbit the Sun.
The images Cassini sent back to Nasa show that four pixels are brighter than what would be expected from a reflection of the Sun, indicating something rougher on the surface, or a wave.
According to Jason Barnes, who presented the research, the chances of Cassini passing at just the right moment again before its mission ends in 2017 are fairly low.
He also highlighted the very small movement seen on Punga Mare: "Don't make your surfing plane reservation for Titan just yet," he said of the miniscule waves.