An astronaut on a strange planet finds that the acceleration due to gravity is two times greater than that on earth. Which of the following could explain this?
(a) The mass of the planet is half that of the earth's but its radius is the same.
(b) The radius of the planet is half that of the earth's but its mass is the same.
(c) Both the mass and the radius are twice the earth's values.
(d) Both the mass and the radius are half the earth's values.