The Cassini spacecraft has identified a possible ice volcano on Saturn's moon Titan, according to Nature magazine.
The circular feature has been interpreted as a cryovolcano
The supposed cryovolcano shows up in images as a bright, circular, domed region about 30km in diameter with two possible flows extending westwards.
It may be formed by an upwelling of hot ice from the interior, scientists say.
The analysis of Titan's surface by the Vims instrument on Cassini also appears to show there are no methane oceans on the moon, as some had suggested.
In Nature, Christophe Sotin and colleagues argue that the dome probably formed as plumes of icy material rose to the moon's surface before releasing methane gas into the atmosphere.
The spectral data from the Vims images, which give scientists information on what the object is made of, suggest the dome and its "flows" are not composed predominantly of water-ice.
The researchers claim that other explanations for the circular feature, such as it being a cloud, or the accumulation of particles similar to a sand dune, are unlikely.
But Louise Prokter of Johns Hopkins University in Maryland, US, said the images were not of sufficient resolution to provide details below a few hundred metres, and suggested the dome might be an impact crater.
She suggested that, if the feature was indeed an icy volcanic dome, it could be formed by nitrogen ice breaking through the surface.
The Visual and Infrared Mapping Spectrometer (Vims) can discern wavelengths of light in the visible and infrared range of the spectrum in order to penetrate the thick organic haze which obscures Titan's surface.