November 20, 2018 | David F. Coppedge

Another Method to Heat Enceladus Falls Short

How do you power geysers emitting more heat than Yellowstone on a little moon for billions of years?

Enceladus is still erupting. Some 100 vents shoot water vapor, gas and dust outward at supersonic speeds, creating an entire ring around Saturn (the E-ring). Has it been doing this for 4.5 billion years? Planetary scientists have been desperate to find heating sources that can sustain this activity for the billions of years they believe the tiny ice moon has existed. A new attempt published in Icarus falls short (again). Notice that the six authors of the paper would not worry about this if previous models of tidal flexing had solved the problem of keeping the activity going.

Do tidally-generated inertial waves heat the subsurface oceans of Europa and Enceladus? (Rovira-Navarro et al, Icarus). Their proposed heat source is too small – way too small, by orders of magnitude.

Saturn's moon Enceladus with "Tiger Stripes" fissures where geysers erupt

Saturn’s moon Enceladus with “Tiger Stripes” fissures where geysers erupt

Some of the moons of the outer solar system harbour subsurface liquid oceans. Tidal dissipation plays an important role in preventing these oceans from freezing. In the past, most studies considered only tidal dissipation in the solid layers of these bodies (rock and ice). Recently, new studies considering tidal dissipation in the oceans of these moons have appeared. All of them make use of the shallow water approximation. However, the use of this approximation might not be adequate. Here we consider the linear non-hydrostatic three dimensional response of these oceans to tidal forcing with the full Coriolis force. To do so we consider an ocean of homogeneous density contained within a perfectly spherical shell and neglect the effect of the ice shell. We force the ocean with a time changing tidal potential and observe patterns of periodic inertial waves that take energy from the global tidal forcing and focus it along thin shear layers that propagate in the fluid. We focus on Europa and Enceladus, showing that inertial waves result in fluid flows of significant amplitude (a few cm/s).

Great idea! Does it work?

Nevertheless, we find that under the previously mentioned assumptions tidal dissipation due to inertial waves is several orders of magnitude smaller than Europa’s radiogenic heating and Enceladus’ observed heat flux.

Back to the drawing board. The answer is: in futureware! “Finally, we propose additional dissipation mechanisms that might play a relevant role in Europa and Enceladus and could be further investigated.

They’ve been at this for at least 13 years now, and even earlier before the geysers were actually observed. Enceladus, Europa and Io remain prime candidates for arguing that the solar system cannot be billions of years old. But those are just three; every other body, from comets to rings to planets, from Mercury to Pluto, have similar problems. And that’s not getting into evidences of youth at our own planet, like our magnetic field. Don’t get me started. I could spend two hours talking about this, sharing pictures and quotes from secular sources.

 

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