A team of U.S. researchers using data from NASA’s Cassini spacecraft has discovered 101 active geysers erupting on Enceladus, the sixth-largest moon of Saturn.
After the first sighting of geysers on Enceladus in 2005, planetary scientists suspected that repeated flexing of the moon by Saturn’s tides as the moon orbits the planet had something to do with their behavior.
One suggestion included the back-and-forth rubbing of opposing walls of the fractures generating frictional heat that turned ice into geyser-forming vapor and liquid.
Alternate views held that the opening and closing of the fractures allowed water vapor from below to reach the surface.
To determine the surface locations of the geysers, University of California and Space Science Institute scientists employed the same process of triangulation used historically to survey geological features on Earth, such as mountains.
When they compared the geysers’ locations with maps of thermal emission, it became apparent the greatest geyser activity coincided with the greatest thermal radiation. Comparisons between the geysers and tidal stresses revealed similar connections.
However, these correlations alone were insufficient to answer the question: what produces what?
The answer came from comparison of the survey results with high-resolution Cassini VIMS data.
Individual geysers were found to coincide with small-scale hot spots, only a few tens of meters across, which were too small to be produced by frictional heating, but the right size to be the result of condensation of vapor on the near-surface walls of the fractures.
This immediately implicated the hot spots as the signature of the geysering process.
“Once we had these results in hand, we knew right away heat was not causing the geysers, but vice versa. It also told us the geysers are not a near-surface phenomenon, but have much deeper roots,” said Dr Carolyn Porco of the Space Science Institute in Boulder, Colorado, who is the lead author of the paper published in the Astronomical Journal.
Carolyn Porco et al. 2014. How the Geysers, Tidal Stresses, and Thermal Emission across the South Polar Terrain of Enceladus are Related. Astronomical Journal 148, 45; doi: 10.1088/0004-6256/148/3/45