Dying Europa

Science Daily was low on astro news lately. That long weekend where we honour Martin Luther King (PhD*) by preventing public schoolkids from their education likely affected that. Today came a dump of information: axions btfo again, carbonaceous meteors, nitrogen from the early inner solar-system. There is also this.

Our planets tilt, to varying degrees, Jupiter only inclining three (3)° and Venus being nearly upside down. Saturn tilts 27°. The argument made this week is that when a moon is large and also far from the planet, the moon both gets affected by other planets (usually in resonance) and acts like a lever to tilt the main one. Saturn is coming to resonance with Neptune; Jupiter, with Uranus. For Saturn, the big moon is Titan, and Titan is both pulling away from Saturn and tilting Saturn's orbit. The article also reminds its audience of Jupiter. I'd missed that.

Jupiter will not be 3° forever. It will tilt, as its moons pull away from it.

This implies that Europa and Ganymede will have less internal heat and, also, less radiation from Jupiter - Jupiter itself will be cooling internally over this time, and will take less tides from its moons. The sun will be heating Jupiter's outer layers and its moons, in those billion-year scales. The moons'll also acquire "seasons" as they tilt with respect to the ecliptic.

This means, I think, that Europa's ocean will freeze, since it is driven from the inside not outside. The other part of Europa will go less "ice" and more "snow" as the radiation sublimes the water off and, in "winter", drops it down again. The insulation will be better thus delaying radiation into space, but still.

The good news for Earth colonists is that Ganymede, further from Jupiter, will be easier to land on and leave from (less delta-V); and will take less radiation from Jupiter. It trades that for more insolation but solar is a more useful irradiance, as solar power.

Callisto will be even better off in terms of delta V and energy; it never had much rad from Jove. They tell us Callisto at 400.5 hours is not in resonance with the other moons. By that they mean not Laplacian. If Callisto revolved 400.65 hours that is 3 months : 7 Ganymede months (G'month=171.7 hr). Maybe the two inner moons might jostle that. Anyway, if it is jostled, 457.8 hours at 3:8 is coming then 516 at a cool 1:3. Those stages might buy the Europan dynamo a little more energy.