Scientists have mapped at least 101 geysers on Enceladus, one of Saturn's moons, based on images captured by NASA's Cassini spacecraft, reported.
Two published online Monday in analyze images of Enceladus captured during the last seven years.
The icy moon, which measures about 310 miles wide, has four "tiger stripe" fractures that have long puzzled scientists. Geysers were first spotted erupting from these fractures in 2005. One theory is that the 101 geysers, which spurt water vapor and ice, happen when the tiger stripes' walls create frictional heat by rubbing together.
Another hypothesis is that the geysers stretch down underneath the moon's icy shell to reach an ocean of liquid water deep beneath its surface.
Using heat-sensing instruments, scientists collected high-resolution data in 2010 showing that geysers were found in conjunction with "small-scale hot spots," said a California Institute of Technology .
At just a few dozen wide, smaller hot spots aren't big enough to be produced by frictional heating; however, their size indicates that they can occur due to condensation of vapor on "tiger stripe" walls close to the surface.
"Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa," Carolyn Porco, who led the Cassini imaging team from the Space Science Institute in Boulder, Colo., and was the lead author of the first paper, said in a statement. "It also told us the geysers are not a near-surface phenomenon, but have much deeper roots."
The second study found that the geysers vary in brightness depending on the moon's location as it revolves around Saturn, something likely influenced by the "tidal heating" generated by the gravity of Saturn and another moon.
Launching from Earth in 1997, the Cassini mission comes from a collaboration between NASA, the European Space Agency and the Italian Space Agency. The $3.2 billion project culminated in Cassini's arrival at Saturn's orbit in 2004. The spacecraft will continue to gather data about the sixth planet from the sun until September 2017.