Why are all planets and moons in solar system basically round?
Gravity doesn’t make so much sense. If every body has gravitational force, then the forces would create multiple rocks. But the way planets and moons were created, might explain more. After the so-called “Big Bang” huge amounts of mass started moving all around in extraordinary speeds. After a while, they all collided together and formed bigger masses. Now, after they collided, all of their energy became kinetic energy and heat. Some bits of these masses broke apart, creating comets or other bodies, and the rest of them came together to form a bigger body. As they grew bigger, the forces of gravity eventually centered and the formed planet became round in shape. Many planets are not perfectly round in shape, which also proves this theory, since not all bits were round to begin with. Also, the stars are completely round because they are mostly liquid!
Gravity is the main force responsible for shaping large objects such as planets. Deviations from spherical shape can be either bumps (basically mountains) or pits (wholes or craters). A mountain that becomes too large will be crushed by its own weight. Imagine a lump of viscous honey on a plate, it will eventually flow into a flatter shape. A similar process applies to very deep wholes: they would collapse, pretty much as a deep whole dug in dry sand. The sperical shape is stable simply because it distributes tension evenly throughout the body of the planet. Every point on the surface is under roughly the same stress, so there is no where to collapse to. Water drops (or gas bubbles in a liquid) also assume this shape for the same reason: equalizing the tension on all points on the surface. Although in the case of liquid drops and gas bubbles the force is due to surface tension rather than gravity. asteroids and comets, being smaller than planets, have weaker gravity and therefore do no
