There were some answer comments at Is it possible to make the Sun spin a coin in space? that could be a question in their own right, so here it is.
Posit that we have a coin in space, on both faces half reflective and half absorptive, as described in the answer. It is in a circular orbit in the invariable plane, 1AU from Sol, starting out at (let's say) 274K. Ignore all of the planets, moons, dust grains, and other bodies for the purposes of this thought experiment.
Various things are acting upon this coin: including solar radiation, the solar wind, solar gravity, and indeed cosmic rays. And posit that it is made of a ferrous metal. It can hold electric charge and have a permanent magnetic field. It starts out uncharged, unmagnetized, and non-rotating. It can, of course, emit radiation. If they matter, assume the size and mass of a €1 coin.
Assume that we have the entire predicted future main sequence lifetime of Sol to play with, if needs be. But we're not looking so far forward that things like evolution into a red giant or proton decay are relevant to our thought experiment. Nor will there be any closely passing stars or suchlike.
What is the (likely) end state? If it depends from some conditions, what are they? Some possibilities, not necessarily exhaustive:
- Will the coin end up melting?
- Will the coin disintegrate?
- Will the coin end up intact, but so far away from Sol that solar influences become negligible?
- Will it reach Solar escape velocity?
- Will, contrariwise, the orbit decay into Sol?
- Will the coin end up spinning so fast that relativistic effects becomes a significant concern?
- Will the coin end up spinning, but not that fast?
- Will the coin, contrariwise, end up not spinning at all?
- Does the end state depend from what the orientation of any spin axis is and the orientation in which the faces were divided in half? If so, how?
