Originally Posted by
drewmandan
This belief that planets cannot collide inelastically, is this based on some deep physical insight or pure speculation? In fact, the general rule is the larger the objects get, the more inelastic collisions get. For example, atoms and molecules cannot be permanently deformed by collisions (or else DNA would be impossible!), but billiard balls, if hit hard enough, can take dents. Moving up in scale, cars get enormously deformed in collisions, rather than simply bouncing off one another. Moving up again, have you ever seen a tall tower fall over sideways? The tower always splits at least once, because no material known to man is strong enough to prevent a large object from behaving inelastically. Moving up in scale again, we get to earth quakes causing a local region of the crust to liquifact, or in other words causes stone to turn to liquid. And once we get up to the scale of planets, most collisions look like two blobs of liquid colliding, because planets are made of rock, and no natural rock can come within even an order of magnitude of the strength required to behave elastically.
U R RONG