by gvann » Fri Apr 01, 2016 1:14 pm
"Europa follows an elliptical path". I didn't think so.
I remember reading an article in Science magazine in February, 1979, about one week before the arrival of Voyager 1 at Jupiter. From what I remember of the article, the authors noted that the orbits of the Galilean satellites have virtually no eccentricity. However, because they are locked in mutual resonance, the gravitational interaction between the satellites causes an "effective" eccentricity whereby the tidal deformation induced by Jupiter varies with time.
The article went on to calculate the amount of energy dissipated in the satellite Io as a result of such varying tidal deformation. It concluded that the dissipated energy was large enough that volcanism might occur extensively on Io.
A week later Voyager 1 discovered Io's volcanoes.
From what I understand, the same happens with Europa: The orbit has no eccentricity, but the gravitational interaction with the other satellites causes Europa to experience variations in the tidal deformation induced by Jupiter. The associated energy is much less than for Io, and is not sufficient to cause volcanic activity; but it's sufficient to keep a large fraction of Europa's water in a liquid state, and provides a steady internal source of energy.
The liquid water on Europa lies under a layer of ice 10-30 km thick. Even with Europa's weak gravity, compared to Earth, pressure under that layer is going to be quite large. Hence the comment by Joe25 about the atmosphere being heavy at the Europa restaurant.
The ice layer blocks radiation very effectively. I am guessing that the bulk of radiation in Europa's subsurface ocean is due to solar and cosmic neutrinos. I wouldn't worry much about it.