Why does the equatorial diameter of a planet affect its equatorial surface gravity?
Larger diameter does not, in and of itself, equal a greater surface gravity. In fact, if thet were the *only* thing you changed between two objects, the larger one (in radius) would have lower surface gravity than the smaller one (in radius), assuming the mass of each were the same. Surface gravity can be calcualted by mass and distance (from the center of mass of the planet, usually referred to in physics courses as “radius”). But a greater distance actually *lowers* the gravity, if the mass were unchanged. The reason why the planets with larger diameters, in general, have greater surface gravity, isn’t because they are physically larger, but because they have so much more mass. If an object with the diameter of Pluto, for example, had the same mass as Jupiter, that object would have a tremendously higher surface gravity than Jupiter would.
