Clearly the eccentricity is one key here, but I'm not sure that the acceleration difference is the right metric. The basic paper that pointed out the likelihood of volcanoes on Io is not that complex --
The key is equation (7), which gives the energy dissipated by a solid body due to its eccentric orbit. It's quadratic in eccentricity, but there are other key factors that would vary from Mercury to Io.
The paper above is remarkable. It's an amazing chain of basically armchair logic that leads to the likelihood of volcanism on Io.
Is your use of "armchair logic" a criticism of the theory that Io is volcanic largely because of tidal energy?
I often wonder about the results of planetary geology. Even the interior of the earth is still not very well understood, and most of the methods we use to understand it (e.g. seismometers) are not yet usable outside earth.
Why would acceleration difference not be the right metric? The Peale model is different because it takes material properties like rigidity into account - but let's keep in mind here that Mercury's eccentricity is 0.2 whereas Io's is 0.004!
That's kind of a bold statement though. If tidal heating is in your opinion not caused by a gravity differential, you're going far beyond and outside the source you linked to, and I would like to hear what alternative you're proposing. The "conventional" explanation for tidal heating is that a body is being squeezed repeatedly, for which the changing gravity gradient I calculated does seem an appropriate measure.
The paper you linked to used eccentricity, whereas I used periapsis and apoapsis - it's the same thing mathematically. Not sure where this "clearly eccentricity is the key" thing comes from when I just told you that Io's orbit is nearly circular.
I do like the materials science aspect of the article you linked to in regard to taking rigidity of the body into account, but at a very basic level the problem remains that Io's orbital shape alone doesn't yield enough of a change over time to account for a lot of tidal heating - certainly not compared to Mercury.
http://www.es.ucsc.edu/~pkoch/EART_206/09-0205/Peale%20et%20...
The key is equation (7), which gives the energy dissipated by a solid body due to its eccentric orbit. It's quadratic in eccentricity, but there are other key factors that would vary from Mercury to Io.
The paper above is remarkable. It's an amazing chain of basically armchair logic that leads to the likelihood of volcanism on Io.