Question

Can a planet two, three, or even ten times the size of earth have the same gravity?

For example, I heard that a planet that is two or three times the size of earth but equal or close to the density earth has can have the same gravitational pull. Would that mean that if we were to find a planet with these characteristics would we be able to walk on its surface an experience little to no change in our weight?

Answer 1

A planet with up to around twice the radius or eight the volume of the Earth could have the same gravity.

Explanation:

The gravity of a planet, or other body, is proportional to its mass.

The density of the Earth is about 5.51 g/`cm^3`. A planet with double the volume of the Earth would have to have half the density to have the same mass and hence the same gravity. Now 2.75 g/`cm^3` is about the density of some of the lighter rocks.

A planet with eight times the volume of the Earth would require a density of about 0.7 g/`cm^3`. This is about the density of the gas giant Saturn which is the least dense of all of the planets in our solar system.

Note that when referring to a planet being double the radius of Earth, it's volume goes up as the cube of the radius which is a factor of 8.

So a planet with up to twice the radius, or 8 times the volume, could have the same gravity as Earth.