Could a "bouncy planet" work in principle?
Would it be possible to have a planet created by a God - but still obeying the known laws of physics - to have a bouncy surface that would be strong enough to bounce any large incoming matter, like asteroids, back into space?
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1 answer
First, the object hits:
The Atmosphere.
Earth's gasses and most other like-fluids as we know them would exert pressure and friction on any incoming objects, the objects would heat-up on the surface ablating in the process, as the heat penetrates, the objects (say take a typical comet - part water-ice and part rock) - parts of them would heat faster than others and expand, breaking the object apart.
One of the "tricky bits" is objects starting to vaporize and massively heat-up in the atmosphere before they even hit a surface - if they are able to bounce, then they'll suffer the same process of heat-ablation and breakup on the way out.
Unless:
Unless the atmosphere consists of a friction-less super-fluid, which exist in labs - if not on Earth otherwise. Liquid helium is one possibility, if god is involved, then I'm sure they know more than I about possible alternative liquids/gasses or mixtures of arcane compounds which would behave the same way.
Then the object hits:
The Surface:
Most objects (rock, wood, even water) have elastic properties with a defined limit - if you throw a glass marble against concrete, if it doesn't shatter, then it will bounce off at the opposite angle from which it was thrown. But the marble shattering is what happens when an object accelerates even just by gravity into a planet's surface, churning-up the ground, throwing material upwards to be scattered for miles creating a massive impact crater for us to remember it by.
Unless:
Perfect elasticity. The Planet's surface and some distance beneath is made of a material that exhibits this property. Ie. any mechanical energy directed into it is resisted with equal force in the direction it is applied with no energy being transformed into heat your object is simply reflected off the surface as if it were a child on a trampoline.
Alex.P is quite correct, an object would need to be made of similar material or be otherwise very resilient. We simple humans don't have such a substance at present (but we're looking into it: meta-materials), but then again what are we compared with a deity with knowledge of all possible materials.
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