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Icy Saturn moon ‘may be active’ Icy Saturn moon ‘may be active’
(about 1 hour later)
By Paul Rincon Science editor, BBC News website, The Woodlands, TexasBy Paul Rincon Science editor, BBC News website, The Woodlands, Texas
Nasa's Cassini spacecraft has spied possible signs of geological activity on Saturn's icy moon Dione.Nasa's Cassini spacecraft has spied possible signs of geological activity on Saturn's icy moon Dione.
It sees features that resemble hot fissures and indications of a possible ice volcano on the satellite.It sees features that resemble hot fissures and indications of a possible ice volcano on the satellite.
The fissures look remarkably similar to the "tiger stripes" found on Saturn's moon Enceladus, which spew powerful jets of water into space.The fissures look remarkably similar to the "tiger stripes" found on Saturn's moon Enceladus, which spew powerful jets of water into space.
On Dione these features may now be idle, but other lines of evidence suggest some activity is ongoing.On Dione these features may now be idle, but other lines of evidence suggest some activity is ongoing.
The new findings suggest this saturnian moon could be a more dynamic place than was previously supposed.The new findings suggest this saturnian moon could be a more dynamic place than was previously supposed.
However, scientists are yet to find any signs of heating within Dione - as they have done on Enceladus.However, scientists are yet to find any signs of heating within Dione - as they have done on Enceladus.
Dr Bonnie J Buratti, from Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, presented the results at the 43rd Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas.Dr Bonnie J Buratti, from Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, presented the results at the 43rd Lunar and Planetary Science Conference (LPSC) in The Woodlands, Texas.
The case for activity on Dione relies on several different lines of evidence.The case for activity on Dione relies on several different lines of evidence.
Observations of Saturn's magnetic field appear to suggest a plume of particles emanates from Dione. Previous bservations of Saturn's magnetic field have picked up a stream of charged particles originating from Dione's surface.
In addition, scientists announced earlier this month that they had detected a thin oxygen atmosphere around the moon.In addition, scientists announced earlier this month that they had detected a thin oxygen atmosphere around the moon.
But the most obvious evidence, said Dr Buratti, was to be found in the moon's surface features. One region in Dione's leading hemisphere is relatively free of craters, which can result when a planetary surface is partially melted by a source of heat.But the most obvious evidence, said Dr Buratti, was to be found in the moon's surface features. One region in Dione's leading hemisphere is relatively free of craters, which can result when a planetary surface is partially melted by a source of heat.
Images from Cassini also reveal the presence of so-called rampart craters, a type of depression caused when a space rock slams into soft material.Images from Cassini also reveal the presence of so-called rampart craters, a type of depression caused when a space rock slams into soft material.
"We also see what I like to call a 'palaeo-tiger stripe', both on Tethys (another Saturnian moon) and Dione. It looks like a fossilised tiger stripe," the JPL researcher explained."We also see what I like to call a 'palaeo-tiger stripe', both on Tethys (another Saturnian moon) and Dione. It looks like a fossilised tiger stripe," the JPL researcher explained.
A feature resembling a cryovolcano has been spotted in the region that is depleted of craters. Cryovolcanoes have so far been found on Enceladus, Neptune's moon Triton, and - debatably - on Saturn's moon Titan. They get their name because they erupt water-ammonia or methane instead of molten rock.A feature resembling a cryovolcano has been spotted in the region that is depleted of craters. Cryovolcanoes have so far been found on Enceladus, Neptune's moon Triton, and - debatably - on Saturn's moon Titan. They get their name because they erupt water-ammonia or methane instead of molten rock.
The discovery of geysers on Enceladus, and the deduction that they are supplied with liquid water by a sub-surface ocean, has been one of the science highlights of Cassini's mission.The discovery of geysers on Enceladus, and the deduction that they are supplied with liquid water by a sub-surface ocean, has been one of the science highlights of Cassini's mission.
The heat that enables this geological activity on Enceladus comes from friction resulting from the way this moon interacts with Saturn's gravity.The heat that enables this geological activity on Enceladus comes from friction resulting from the way this moon interacts with Saturn's gravity.
Observations of Saturn's magnetic field seem to suggest that Dione are emitting particles.
Dr Linda Spilker, project scientist on the Cassini mission, explained that if there was any activity at Dione, it would be at a lower level than on Enceladus.Dr Linda Spilker, project scientist on the Cassini mission, explained that if there was any activity at Dione, it would be at a lower level than on Enceladus.
"We haven't detected obvious jets, like we have at Enceladus. But we're still looking," Dr Spilker, who is also based at JPL, told BBC News."We haven't detected obvious jets, like we have at Enceladus. But we're still looking," Dr Spilker, who is also based at JPL, told BBC News.
During the question and answer session following Dr Buratti's talk, John Spencer from the SouthWest Research Institute revealed that Cassini's CIRS instrument had been searching for a heat signature from the moon, but so far failed to find one.During the question and answer session following Dr Buratti's talk, John Spencer from the SouthWest Research Institute revealed that Cassini's CIRS instrument had been searching for a heat signature from the moon, but so far failed to find one.
Dr Buratti agreed that evidence of hotspots would provide a "smoking gun" in the case for geological activity on Dione.Dr Buratti agreed that evidence of hotspots would provide a "smoking gun" in the case for geological activity on Dione.
Paul.Rincon-INTERNET@bbc.co.ukPaul.Rincon-INTERNET@bbc.co.uk