The correct answer is D: The constant g is different on Mars.
The weight of an object is determined by the force of gravity acting on it, and this force is represented by the equation W = mg, where W is the weight, m is the mass of the object, and g is the acceleration due to gravity. On different celestial bodies, the value of g can vary due to differences in mass and radius.
Option A is incorrect because the mass of the object (m) is a constant and does not change based on the location. Option B is also incorrect since both the mass and radius of Mars are significantly less than those of Earth. Option C is not accurate because the distance from the Earth's center does not affect an object's weight; it is solely determined by the gravitational force acting on it.
On Mars, the acceleration due to gravity (g) is weaker than on Earth due to Mars having less mass. Therefore, the correct explanation for the difference in weight is that the constant g is different on Mars compared to Earth. In summary, the weight of an object on Mars is less than on Earth because the gravitational acceleration on Mars (g) is weaker.
Therefore, the correct answer is D: The constant g is different on Mars.