i see his point but it doesn't really hold
This articial really just doesn't hold any water at al,l other than mere hopeful speculation.
The main (be all and end all) driving force in this universe is gravity. Of all of the laws of physics gravity is the one that makes this universe work and it controls every aspect of it.
Without gravity this universe/galaxy/sun/planet/moon could not / would not exsist.
All life forms (carbon based) build their structure based on the gravitational force put upon them.
We have spines for very good reason. Our own bodies are build around a gravitational force of one G and our on travel to our planets relies heavy on our own ability to withstand the gravitational forces put upon us when we get there.
These same rules would apply to ETs one would assume.
Assuming that a planet such as jupiter-like sustains 5 or 6 moons. They will all be in different gravitational orbits and as such there will be different forces on the surface.
ET could see those moons, send probes to them, but could not visit for fear of being crushed to death.
In fact the human race is incrediably lucky to have a moon of our only to fuel our own space endevours.
A good example would be put a human on jupiters surface (if there was on) would be a little bit pointless as the human would be a smoothy in seconds. Aslo if we visited Europa (widely thought to harbour the only chance of life in this solar system) again we'd be crushed by the gravitational forces put upon it by jupiter.
The only way life could move from one moon to another would be if the two moons were in exactly the same orbit of the same planet thereby having the same gravitational forces. Highly unlikely but possible. Then however, the planet would be on the perceved "Dark Side" of the planet and Et wouldn't know it exsisted until they started ther eown space race.. ergo muting the point!