Earth gets, on average, 340 watts per square meter of sunlight (more at the equator than the poles and more during the day than at night) for a total flux of 1.7 10^17 watts. Earth also has a geothermal heat flux (partially from primordial heat of formation, partially tidal heating, partially radioactive heating) of 4.7 10^13 watts for 0.087 watts per square meter (concentrated in hot spots of course). Our geothermal flux is thus about 1⁄4000 our solar flux. Only a fraction of the geothermal energy flux will be in a form available to living things, specifically that which causes geochemical gradients to form. Though geothermal effects can also bring deep substances into contact with surface substances and allow them to interact and produce more energy than is contained in the gradient—like serpentinization, by which Fe2+ in particular very deep rock types plus surface water become Fe3+ oxides and hydrogen gas for a net release of energy. I am unprepared to compare the energy of dredged up chemicals to the heat flux. I do know that living things on Earth can easily live off these fluxes at hot springs and vents.
Europa is estimated to receive 7 * 10^12 watts of tidal heating driving geothermalisms (a full seventh that of Earth for something only 0.008 times as massive and 1⁄16 as much surface area as Earth, though one or two other sources I found have estimates a factor of two or three higher). Its radioactive heating is negligible compared to that number. This gives it an average geothermal energy flux of 0.23 watts per square meter, about 1/1500 what we get from the sun, a fraction of which becomes geochemical gradients accessible to life. There will be more geothermal action going on in there than on Earth. Again these geothermal flows could also dig up already-reactive substances from deep below that could react with substances in the ice/ocean, increasing the available energy.
There is indeed a bunch of water cracking happening at its icy space-exposed surface via radiation, with hydrogen sputtering off into space and oxidized compounds winding up in the ice which is believed to circulate down on megayear timescales into the lower layers and potentially into the liquid layers. This would allow another energy source via the oxidation of minerals or hydrocarbons dissolved in the liquids, which life could insert itself into as a middleman.
All the forthcoming numbers I am using are from “Energy, Chemical Disequilibrium, and Geological
Constraints on Europa” by Hand et al. About 4 watts per square meter of sunlight is absorbed by the surface (of about 13 watts of total average incident light), only a tiny fraction of which would cause water-cracking. It gets about 0.125 watts per square meter of particle irradiation. If we assume a ridiculously unrealistically high far-upper-bound of 0.25 watts per square meter of water-cracking which generates oxygen at 237 kilojoules per mole, and that oxidizes iron from, say, a metallic state to rust (about 550 kilojoules per mole of oxygen gas) you get something like half a watt per square meter of oxygen-based energy flow.
That is DEFINITELY a drastic overestimate though. The paper mentioned above goes into some analysis I am utterly unprepared to comment on and suggests that given the surface age of Europa and its energetic environment, up to about 5 * 10^9 moles of ‘oxidants’ are delivered to the interior of Europa per year. Let’s be completely naive and just compare that to the total photosynthetic flux of the Earth, assuming it’s all oxygen. It comes to something like one millionth the photosynthetic productivity of Earth.
Of course, since these matter flows via geothermalisms or crust downwelling are very uneven compared to incident sunlight there will be localized hotspots like our own geothermal vents where things could be much more interesting than the above numbers would seem to indicate.
Earth gets, on average, 340 watts per square meter of sunlight (more at the equator than the poles and more during the day than at night) for a total flux of 1.7 10^17 watts. Earth also has a geothermal heat flux (partially from primordial heat of formation, partially tidal heating, partially radioactive heating) of 4.7 10^13 watts for 0.087 watts per square meter (concentrated in hot spots of course). Our geothermal flux is thus about 1⁄4000 our solar flux. Only a fraction of the geothermal energy flux will be in a form available to living things, specifically that which causes geochemical gradients to form. Though geothermal effects can also bring deep substances into contact with surface substances and allow them to interact and produce more energy than is contained in the gradient—like serpentinization, by which Fe2+ in particular very deep rock types plus surface water become Fe3+ oxides and hydrogen gas for a net release of energy. I am unprepared to compare the energy of dredged up chemicals to the heat flux. I do know that living things on Earth can easily live off these fluxes at hot springs and vents.
Europa is estimated to receive 7 * 10^12 watts of tidal heating driving geothermalisms (a full seventh that of Earth for something only 0.008 times as massive and 1⁄16 as much surface area as Earth, though one or two other sources I found have estimates a factor of two or three higher). Its radioactive heating is negligible compared to that number. This gives it an average geothermal energy flux of 0.23 watts per square meter, about 1/1500 what we get from the sun, a fraction of which becomes geochemical gradients accessible to life. There will be more geothermal action going on in there than on Earth. Again these geothermal flows could also dig up already-reactive substances from deep below that could react with substances in the ice/ocean, increasing the available energy.
There is indeed a bunch of water cracking happening at its icy space-exposed surface via radiation, with hydrogen sputtering off into space and oxidized compounds winding up in the ice which is believed to circulate down on megayear timescales into the lower layers and potentially into the liquid layers. This would allow another energy source via the oxidation of minerals or hydrocarbons dissolved in the liquids, which life could insert itself into as a middleman.
All the forthcoming numbers I am using are from “Energy, Chemical Disequilibrium, and Geological Constraints on Europa” by Hand et al. About 4 watts per square meter of sunlight is absorbed by the surface (of about 13 watts of total average incident light), only a tiny fraction of which would cause water-cracking. It gets about 0.125 watts per square meter of particle irradiation. If we assume a ridiculously unrealistically high far-upper-bound of 0.25 watts per square meter of water-cracking which generates oxygen at 237 kilojoules per mole, and that oxidizes iron from, say, a metallic state to rust (about 550 kilojoules per mole of oxygen gas) you get something like half a watt per square meter of oxygen-based energy flow.
That is DEFINITELY a drastic overestimate though. The paper mentioned above goes into some analysis I am utterly unprepared to comment on and suggests that given the surface age of Europa and its energetic environment, up to about 5 * 10^9 moles of ‘oxidants’ are delivered to the interior of Europa per year. Let’s be completely naive and just compare that to the total photosynthetic flux of the Earth, assuming it’s all oxygen. It comes to something like one millionth the photosynthetic productivity of Earth.
Of course, since these matter flows via geothermalisms or crust downwelling are very uneven compared to incident sunlight there will be localized hotspots like our own geothermal vents where things could be much more interesting than the above numbers would seem to indicate.