Okay, just this once - I had to feed you this! :)
One of the things seen in the Elite: Dangerous Beta 1 is significantly more star systems. Many of these have planetary systems around them, formed at much the same time as the star(s) in the system, or captured during the lifetime of those systems.
In Elite: Dangerous, when we are generating a system procedurally, each planetary system is formed from first principles. Bodies are gradually aggregated over a very long simulated time from available matter, taking into account its chemical composition. Depending on the angular momentum, this might begin to form into a single central body, or into multiple co-orbiting bodies.
As the gases collapse together under the force of gravity, matter tends to orbit these bodies in protoplanetary discs, which in turn further coalesces into smaller bodies within those discs. Tidal forces, orbital resonances and gradual accretion of mass gradually change their orbits, causing collisions, collapse and close encounters – which in turn means bodies might capture each other or fling each other into new orbits or out of the system altogether.
At some point the stars in the system ignite one by one, and the resultant stellar winds gradually drive off the lighter non-gravitationally bound gases.
Over its lifetime (different for different systems) close and not so close encounters with other stellar systems may remove outer planets and capture others, and the outer halo of comets and other bodies may pass through the other system, not just causing destruction, but also depositing lighter elements and compounds (like ice/water) on the bodies in the inner system that may have been lost during the heat of their formative years, making water-based life there possible.
The above processes are all modelled from first principles for almost all of our 400 billion star systems by an Elite: Dangerous system called Stellar Forge.
There are some interesting outcomes from Stellar Forge that are ‘backed up’ by astronomical observations – for example binary planets. During the process of the system forming, both catastrophic collisions (as in the case of Earth) and very close encounters can result in bodies in very similar orbits capturing each other into a wonderful co-orbiting waltz.
We see the early stage of this in the Solar system with the moons of Saturn, Epimetheus and Janus which share an orbit – swapping positions whenever they have a close encounter – but this is not stable in the very long term, particularly not in a gaseous disc where the gases are continually absorbing energy. In such a gaseous disc while planets are still forming and the corresponding slowing of the orbits, this is likely to end up with the bodies eventually co-orbiting each other in an ever less elongated orbit.
Pluto and Charon are another example of an asymmetric binary planet (or dwarf planet as I think we should say these days), likely arising as a result of a close encounter or collision of an unknown body with Neptune, but then the pair eventually ending up orbiting each other, picking up other debris from the collision over time.
We have seen pairs of gas giants in Stellar Forge, co-orbiting each other, each with its own stable moons. When standing on one of those moons you will see both gas giants looming large in the sky.
Even pairs of earth-like planets are possible. In fact if one had life, then it is most likely both would, as meteorite impacts on one would tend to catapult debris to the other and spread the life across.
Bodies can orbit each other very closely indeed. They can even touch – forming a strange dual body with a ‘figure of eight’ or hourglass shape – something predicted by a mathematician called Roche. We see this with stars too – an example of this is the contact binary i Boötis BC – already seen in the Elite: Dangerous Premium Beta.
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