The chances of individual stars of the two systems colliding are infinitesimal.
Deidre gazed after him, fear and hope colliding within her.
There is no reason to doubt that in the case of the fountain also, coalescence is due to differences of potential between colliding drops.
His face was in her thoughts, and the idea of never seeing him again crushed her as surely as colliding with the planet would.
Parked vehicles also have to be taken into account as nothing riles people more than a 26 ton freighter colliding with their car!