Huge plumes of water vapor and ice particles are spewing from Saturn's moon Enceladus at supersonic speeds in a way that strongly suggests they come from liquid water below the icy surface, scientists said.
The research, published in the journal Nature Wednesday, offers new evidence that the moon may harbour an underground ocean of water, meaning conditions might exist that could support life, even if only microbial organisms.
"We think liquid water is necessary for life," Candice Hansen of NASA's Jet Propulsion Laboratory in Pasadena, Calif., who led the study, said in a telephone interview.
"This is more evidence that there is liquid water there. You also need energy, you need nutrients, you need organics. It looks like the pieces are there. Whether or not there's actually life, of course, we can't say," Hansen said.
The Cassini spacecraft in 2005 discovered humongous geysers erupting from fissures near the south pole of Enceladus into space — reminiscent of the famed Old Faithful at Yellowstone National Park in the United States but on a grand scale.
Since then, scientists have debated whether this meant that Enceladus, with a diameter of only 500 kilometres, was hiding a reservoir of liquid water. It is one of about 60 moons of the dramatic ringed planet Saturn.
Based on data collected last year by Cassini's Ultraviolet Imaging Spectrograph instrument, the researchers said the behavior of the plumes supports a mathematical model in which the cracks that extend below the surface act as nozzles that channel water vapor from an underground liquid water reservoir.
The geysers continuously shoot plumes into space at more than 2,090 km/h, the researchers said.
By using the instrument to observe the flickering light of a distant star as the geyser blocked its starlight, the researchers determined that the water vapor comes from narrow jets as it blasts into space.
"We're saying we detected these jets within the plumes and the gas moving at supersonic velocities. And we're saying that this is consistent with the previously developed model that has liquid water at depth" under the surface, Hansen said.
The Cassini spacecraft, operated in a joint U.S.-European mission, flew close over the surface of Enceladus in March and actually through a plume, collecting samples of ice and gas.
"There are only three places in the solar system we know or suspect to have liquid water near the surface — Earth, Jupiter's moon Europa and now Saturn's Enceladus," Joshua Colwell of the University of Central Florida, another of the researchers, said in a statement.
"Water is a basic ingredient for life, and there are certainly implications there. If we find that the tidal heating that we believe causes these geysers is a common planetary systems phenomenon, then it gets really interesting," Colwell added.