What is the minimum mass of an object in space before gravity naturally shapes the object into a sphere?
Small asteroids and other objects can be found in many shapes.
However, at some mass, gravity will automatically shape the object into a sphere. What is this point (like what mass or when does this happen)? And why?
The mass at which this happens depends on the composition and condition of the body in question. The body has to be massive enough for its gravity to overcome the rigidity of its material. If there’s enough force to make the material flow, the object will assume a spherical shape because that’s the lowest energy configuration – everything on the surface of a sphere is at the same gravitational potential, so there’s no tendency for it to fall to another position.
The asteroid Ceres appears to be the smallest spherical asteroid, with a mass of around 10^21 kg, so that sets an upper bound for the minimum size for a rocky object.