Replace one of the moons of Saturn or Jupiter with Earth

[gigabytelord]

It's a very simple question. How would human history, technology and general interest in the cosmos, have changed, been different or progressed differently as compared to real human history if humanity had evolved on a world called earth that was a moon of either a Saturn or Jupiter analog. Feel free to pick your preferred planet. For the purposes of this thought experiment assume that the parent gas giant is placed at a comfortable location within the Goldilocks zone.

[Borgholio]

I'm not sure we WOULD have evolved. If we were placed in the orbit of Ganymede, for instance, our climate would be not even remotely similar to what it is now. If Jupiter were in the Goldilocks zone, the orbit of Ganymede is still a million miles away from the planet. So our distance to the sun would change by 2 million miles over the course of the 7 day orbit. Plus, Jupiter would block the sun for a day or two at a time. Then there's the radiation. Jupiter would bathe the Earth in way more radiation than we get right now, so that would affect evolution, mutation, and cancer rates. On top of that, the gravitational stress would squeeze the Earth constantly, causing way more tectonic activity than we have right now.

So yeah...I doubt we would have evolved. If we did, then the world would be much different than it is now.

[Guardsman Bass]

You'd have to move the Earth farther outward than the current Earth-Moon separation. At that distance (350,000 -400,000), Earth would be a hellish volcanic wasteland bathed in incredibly strong radiation from Jupiter's Van Allen belts (which would be much more intense with 25 times its current solar insolation).

I'm a bit more optimistic at the Ganymede or Callisto separation, even if it does mean the Earth's sunlight varies a bit every few days - the Earth is big enough with a thick enough atmosphere that it could weather it (although it might generate some impressive storm systems). The Earth is big enough that it would likely retain a core capable of generating a strong magnetic field to blunt most of Jupiter's radiation, although it would still be deadly for man or robot to go into space without shielding.

[Borgholio]

The Earth is big enough that it would likely retain a core capable of generating a strong magnetic field to blunt most of Jupiter's radiation

You sure? Jupiter's radiation is incredibly intense.

[Guardsman Bass]

I don't know the exact math, to be honest.

[Me2005]

What about Saturn?

If any of these were feasible, I understand travel between moons in those planetary systems to be pretty reasonable, so it's possible we'd have set foot on multiple other moons.

[GrandMasterTerwynn]

The Earth is big enough that it would likely retain a core capable of generating a strong magnetic field to blunt most of Jupiter's radiation

You sure? Jupiter's radiation is incredibly intense.

Ganymede has an independent magnetic field some three times stronger than Mercury's. It is enough for closed field lines to about +/-30 degrees of latitude. An Earth-sized body with an Earth-sized magnetic field would exist comfortably within Jupiter's magnetosphere. You would even have aurorae on the poles, as our magnetic field would connect to our hypothetical goldilocks-Jupiter and funnel the plasma trapped in its magnetic field down to the poles.

Mind you, at Ganymede-type distances from Jupiter, our hypothetical Earth would experience days that we'd consider to be a week long. Every day would also feature a solar eclipse, as Earth slides into Jupiter's shadow. This would definitely have an impact on early cosmology ... I don't think there's any way a geocentric model of the cosmos would be justifiable even by the time of Aristotle and then Ptolemy (though this depends on what part of the Earth ends up permanently facing Jupiter. If it's Europe and Africa, then Western civilization would lag way behind everywhere else in the science of astronomy ... since the only time you could really get any of it done would be during that daily solar eclipse. On the Jupiter-facing side of Earth, nighttime wouldn't exist as we know it ... a full Jupiter would be intensely brighter than a full Moon. The only things that'd normally be visible would be the other Jovian moons, the brightest planets, and maybe the absolute brightest stars.)

Mind you, this assumes that we'd have civilization at the European latitudes. Depending on how the atmospheric heat transfer works out, an 84 hour night might get quite cold in the "temperate" latitudes. Conversely, an 84 hour day would end up being quite warm in the "tropics" ... for the purposes of this thought experiment, it'd probably be better to assume that this hypothetical Earth/Jupiter system starts out life where Mars is now.

[Guardsman Bass]

Would winters as we recognize them exist on Earth-Moon? They're related to axial tilt with regular Earth, but Earth-Moon might have a drastically reduced axial tilt - both Jupiter and its satellites have low ones.

[Borgholio]

Without an axial tilt we wouldn't have much in the way of seasons as we know them. Our "seasons" would be about a week long. We would have a few days of summer when we are in full sun, a few days of spring / autumn when Jupiter is partially eclipsing the sun, and a few days of winter when the only light we get is reflected off of Jupiter itself or refracted through it's atmosphere.

[xerex]

(though this depends on what part of the Earth ends up permanently facing Jupiter. If it's Europe and Africa, then Western civilization would lag way behind everywhere else in the science of astronomy ... since the only time you could really get any of it done would be during that daily solar eclipse. On the Jupiter-facing side of Earth, nighttime wouldn't exist as we know it ... a full Jupiter would be intensely brighter than a full Moon. The only things that'd normally be visible would be the other Jovian moons, the brightest planets, and maybe the absolute brightest stars.)
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Pardon the dumb question. If the Earth was a moon , then that automatically means that its would be locked with one half facing Jupiter permanently ?

Also how would this affect tides ?

[Borgholio]

If we were tidally locked, we'd still have tides...they just wouldn't be as strong as if we weren't locked. Tides on Earth are caused by the Sun as well, just not as strongly as the Moon.

[GrandMasterTerwynn]

If we were tidally locked, we'd still have tides...they just wouldn't be as strong as if we weren't locked. Tides on Earth are caused by the Sun as well, just not as strongly as the Moon.

Actually, that answer depends on how many other large moons orbit Jupiter along with this Earth. Io and Europa experience wicked tidal forces (on account of orbital resonances with the other Galilean moons,) for example. This Earth may well have some serious tidal action going on.

[Borgholio]

Actually, that answer depends on how many other large moons orbit Jupiter along with this Earth. Io and Europa experience wicked tidal forces (on account of orbital resonances with the other Galilean moons,) for example. This Earth may well have some serious tidal action going on.

True. That's actually how they think Europa manages to maintain a liquid ocean under the crust...constant gravitational and tidal squeezing from Jupiter and the other moons.