Fact 1: The mass of an object causes the gravitational force exerted by that object.

Fact 2: An asteroid is a rock-like object with an irregular shape.

Given the two facts above, answer the question "What causes the gravitational force exerted by an asteroid?" with the following options: 
- a tree falling
 - flow of electrons
 - the shape of the asteroid
 - kinetic energy
 - solid, liquid, gas
 - the mass of the asteroid
 - the sound of the asteroid
 - the color of the asteroid


 

      the mass of the asteroid   