'Ice volcano' identified on Saturn's moon Titan
Scientists think they now have the best evidence yet for an ice volcano on Titan, the largest moon of Saturn.
The Cassini probe has spotted a 1,500m-high mountain with a deep pit in it, and what looks like a flow of material on the surrounding surface.
The new feature, which has been dubbed "The Rose", was seen with the probe's radar and infrared instruments.
Titan has long been speculated to have cryovolcanoes but its hazy atmosphere makes all observations very difficult.
Researchers are now wondering how active this mountain might be, and what sort of lava it could spew.
"Much of Titan's outer material is water-ice and ammonia, and so that's certainly one possible material that could melt at low temperatures and flow on the surface," explained Dr Randy Kirk, a Cassini radar team-member from the US Geological Survey (USGS).
"But there's a lot of organics material in the atmosphere, and deposited from the atmosphere, and maybe coming up from the interior in the form of these volcanoes. [This material could be] waxy or even plasticy," he told BBC News.
Dr Kirk was speaking here in San Francisco at the American Geophysical Union (AGU) Fall Meeting, the world's largest annual gathering of Earth and planetary scientists.
There have been previous claims for ice volcanoes at Titan, but these have never won universal support. Scientists have continued to look however because it is considered an excellent candidate given its frigid conditions: the surface temperature is about minus 180 Celsius.
Dr Kirk and colleagues hope their new data will convince even their sternest critics that a positive identification has now finally been made.
The putative volcano is sited just south of Titan's equator in a sea of sand dunes referred to as Sotra Facula.
The radar instrument on Cassini is able to see through the moon's haze and establish the local topography - scientists can build a 3D model of the ground. The infrared instrument on the probe, on the other hand, can gather some information on the variation in composition of the surface materials. Taken together, Dr Kirk's team says, the two views put forward a compelling case.
"We've seen a mountain that has a crater in, that flows of material coming out and spreading across the surface at some time in the past; and in fact when we looked in more detail in 3D we found that there was more than one volcano in this area. And that's actually very common in volcanic areas of the Earth and other planets."
Jeffrey Kargel, a planetary scientist at the University of Arizona, Tucson, is not connected with the Cassini mission. He told the meeting The Rose was the most likely volcano he had yet seen on Titan.
He said that if the lavas were rich in hydrocarbons, they could have the look of softened asphalt, candle wax or even polyethylene.
"There are many unanswered questions and intriguing possibilities," he told reporters.
"Is Sotra the source of Titan's atmospheric methane? Is cryovolcanism still active at Sotra or elsewhere on Titan? What is the cryovolcanic substance? Is cryovolcanism there explosive or quietly effusive? Might cryo-lavas have dredged up indications of fossils or chemical remains of sub-surface life?"
The Cassini-Huygens mission is a co-operative project of Nasa, the European Space Agency (Esa) and the Italian space agency (Asi).