What size does a planetary body have to be for gravity to force it into a sphere?

Question

What size does a planetary body have to be for gravity to force it into a sphere?

Answer 1

It's not so much size as what mass it is, and it's density.  Water, for example, will form a sphere when it's just a few drops.  But Ceres, the largest asteroid known (now called a dwarf planet), is kinda squarish, and it's as big as Texas.  Mimas, on the other hand, a moon of Saturn, is 200 miles less in diameter than Ceres, but *has* formed a sphere.  

There has to be enough mass and gravity to pull the components of the body into a sphere.  A solid mass of iron won't easily break down, no matter what it's size, but a loose jumble of rocks will probably cursh itself into a sphere when it's a few dozen miles across.  

Answer 2

it does not have size at all, it formed by (the binding forces) which bind all matters and particles together . however a planetary must orbiting around a star. If it is not orbiting, then it is not a living planet, therefore a dead one. which is same as an asteroid.

Answer 3

Density is more important than size. Look at water in zero gravity. The droplets are spherical.

Answer 4

Like the first poster said, it depends on what it's made of.

Once you get like 350-400 kilometres across for icy-rock mixtures, their gravity pulls them into a spherical shape.

Answer 5

That depends on what its made of.

Essentially the force of gravity has to overcome the strengths of the rocks (or ice) that make up the planet.

If we look at the asteroid belt, only Ceres is close to spherical, although Vesta is almost there - so that gives your a size/mass estimate for rocky bodies. I suspect that ices deform more easily, so out in the Kuiper Belit, the limit is probably smaller.

Answer 6

Planets get formed from protoplanetary disks. A disk of gas and dust that rotates around a star, the fragments in that disk collide and merge gradually forming planets!