The icy moons of Jupiter and Saturn are looking more and more like ideal candidates for life beyond Earth. Observations of Enceladus and Europa suggest an ocean beneath the ice where suitable conditions might exist, but how the water is kept liquid is still not perfectly clear.
Now a new model developed by American astronomers Edwin Kite and Allan Rubin has focused on how Enceladus remains an active world. According to the researchers, plumes of vapor erupting from the moon’s fissures are connected to the ocean by "slots" that fill with water during the tidal effects generated by Saturn. The tidal flow of water heats up the ice, so the fissures don't freeze shut.
Their research is published in the Proceedings of the National Academy of Sciences.
"On Earth, eruptions don't tend to continue for long," Kite said in a statement. "When you do see eruptions that continue for a long time, they'll be localized into a few pipe-like eruptions with wide spacing between them."
The strong gravitational forces exerted by Saturn squish Enceladus, both heating up the icy surface and moving the underground ocean. Previously, the light blue stripes, known as "tiger stripes," were thought to be areas where the ice would melt due to frictional heating from the tides. This research shows that it's actually the water being "pulled" up through the fissure.
The strong tidal force from Saturn and the other moons also creates a turbulent flow, which warms up the water enough to melt the surface ice and thus form the stripes and plumes. This also helps to solve a puzzle of why the fissure system doesn't "clog up with its own frost," added Kite.
The Enceladus plumes were first discovered in 2005 by Cassini. The plumes are a continuous feature of the moon, but astronomers observed a five-hour lag between the peak of the plumes' eruption and the most intense tides, meaning it's unlikely the stripes are created by the plumes.
"Because the viscosity of water is so low, I doubted it would produce sufficient heat," Rubin said. "But Kite's calculations show that not only does it produce sufficient heat, it does so while getting the time lag between the peak tidal stresses and the peak plume activity just about right. To me, this is the first model that seems to explain these perplexing observations so naturally."
This research and a study from last week on Europa have added to the interest in these two satellites. Hopefully, in the near future, we can send a mission to explore the oceans of one of these worlds.