The basic ideas of the Ganymede hypothesis are not complicated. Starting from the most common idea of solar systems forming up from swirling masses of dust or plasma, you would anticipate the spin axes of the bodies in a solar system to all be roughly perpendicular to the plane of the system. That, of course, is not what we find within our own system.

Within our system, we have the sun, Jupiter, and Mercury which do look sort of like that, all with axis tilts less than 10°. You should assume that those three bodies were an original system. But it starts to get strange from there. Venus and Uranus have oddball axis tilts and each has its own separate little story. But the other four main bodies in the system, Neptune, Saturn, Mars, and Earth all have the same roughly 26° axis tilt. That is a huge anomaly.

You have to assume that those four bodies were captured as a group, probably recently, but then you get to the question of why being captured as a group would cause all four to have roughly the same axis tilt. 

The answer is as follows: early solar systems do not form up from swirling clouds of dust being acted upon by gravity. They're formed by the Birkeland currents which you see in space which are created by the charge separation over immense distances in space. A Birkeland current is a twisted pair of currents looking somewhat like an RNA/DNA string. At the point at which these pairs of currents cross each other, you have electrical short-circuiting and what is called Z-pinch effect. Those pinch points have more than enough power to agglomerate the plasma of space into much more solid objects, proto-stars and stars. A Birkeland current with such bodies at its pinch points is called a Herbig/Haro string, basically an early solar system. These things look like a shish kebab in which the shishes are lit up, that is, like a string of Christmas tree lights with the wires pulled taught.

What appears to be the case is that the southern system (Neptune, Saturn, Mars, Earth), some tens of thousands of years ago, was still in the form of such an electromagnetic alignment and flew into the plane of the sun/Jupiter/Mercury system from the South at a roughly 26° angle and, as the individual bodies peeled off and began to orbit the way they do now, ordinary gyroscopic force caused them to retain that 26° angle of approach in the form of axis tilts.

That also says that, prior to that final capture event, our system was a double system with a very bright northern part, and then a very dark southern part. Rocky bodies like Earth and Mars aligned with a dwarf star such as Saturn was at that time, will most often be INSIDE the plasma heliosphere of that dwarf star. Radiant energy will bounce off the interior of that plasma heliosphere and then on to the Rocky bodies from every direction so that something living on that body won’t just freeze, but the entire middle part of the light spectrum simply be missing.

The literature speaks of red and Brown dwarf stars but the reality is that what you would get within such a system would be a very deep dark purple, hence the notion of a “Purple Dawn” which you read about in mythology books and which the oral traditions of the oldest human groups describe. Thus also amongst the old creatures of the earth (lemurs, tarsiers, Bush babies, owls etc.) and particularly amongst dinosaurs and hominids such as the Neanderthal, you see huge eye sockets and eyes adapted for such a darkish environment. Neanderthal eyes sockets are very much larger than ours.

Humans and Dolphins have the smallest relative eye sizes of advanced creatures; you have to assume that they arose within the bright side of that ancient double system. And there was one particular place within that ancient northern system, i.e. Jupiter’s largest moon, Ganymede, which would have been a freshwater ocean world under those conditions with both islands and floating bergs of pumice and luxuriant vegetation. In other words, an ideal home world for humans.