Scientists working on NASA's Cassini mission have discovered no less than 101 distinct geysers on Saturn's small icy moon Enceladus. Just as exciting is the possibility that liquid water may be reaching the surface — making Enceladus a major target for future exploration.
Back in 2005, NASA's Cassini spacecraft sent back images showing what appeared to be plumes of water vapor spewing out from fractures, called "tiger stripes," near Enceladus's southern pole (similar to what was recently detected on Europa, another icy moon with a subsurface ocean). Gravitational measurements made from 2010 to 2012 proved that these plumes were originating from a large reservoir of liquid water underneath the moon's icy surface. Furthermore, NASA also learned that Enceladus is comprised of two layers: an external icy shell and an internal rocky core made of silicates. This tiny moon could therefore feature a potentially habitable environment — one that could even be more hospitable to life than Europa.
But the story is getting even better. Cassini mission scientists have mapped 101 active geysers — and they're fairly certain that liquid water is reaching the surface from the moon's underground sea.
For the past six-and-a-half years, Cassini's camera's have surveyed the south polar terrain of Enceladus, the region renowned for its four prominent "tiger stripe fractures."
Analysis of Cassini's scans have revealed the presence of 101 individual geysers. These geysers, which shoot tiny icy particles and water vapor, appear to be situated around small hot spots. In addition, the most significant geyser activity happens where the tidal stresses on the surface caused by Saturn's immense gravity are the greatest. It's very possible that these two phenomena are linked, pointing to the geysers' origin.
To locate the sources of the geysers, the scientists compared the geysers' locations to low-resolution maps of thermal emissions. It became apparent that the greatest geyser activity matched with the greatest thermal radiation. Comparisons between geysering and tidal stresses also provided a good match.
The Cassini researchers discovered that the individual geysers were coinciding with the small-scale hot spots, which only measure a few dozen feet across. There's no way these small features could be caused by frictional heating — but they are the right size to be the result of condensation.
So heat is not causing the geysers — it's actually the other way around. They are not a near-surface phenomenon (e.g., something caused by surface friction), but a phenomenon with much deeper roots. The researchers say the only plausible source of the material forming the geysers is the sea known to exist beneath the ice shell.
Another implication of this work is the possibility that seawater may be reaching all the way up to the surface — and not just as droplets entrained in vapor but as a liquid. The researchers also found that narrow pathways through the ice shell can remain open from the sea all the way to the surface if filled with liquid water.
As noted in a CICLOPS statement:
The fact that Enceladus' sea is salty, laced with organic compounds, spouting into space, and maybe even rising up to the surface has raised this particular Saturnian moon as a major target for future exploration.
And as noted by Carolyn Porco, leader of the Cassini imaging team from Space Science Institute in Boulder, Colorado:
For me, the finding of an easily sampled, habitable environment within Enceladus has been Cassini's most profound discovery. Many of us are now asking whether a second origin of life in our solar system could have occurred on this little moon.
Whoa. So what are we waiting for? Sounds like we need to get our asses to Enceladus.
Images: NASA/Cassini-Huygens/C. Porco et al./JPL/Astronomical Journal.