PARIS (AFP) - The Moons highlands, long a mystery, may have been thrown up billions of years ago by a slow-motion collision with a smaller companion moon knocked off its orbit, says a study released Wednesday. With mountain ranges topping 3,000 metres (10,000 feet) and deep craters, the farside of the Moon bears scant resemblance to the smoother surface and shallow lava-filled maria, or seas, on the nearside visible from Earth. Scientists have proffered many explanations for this split personality, also known as the lunar dichotomy. Some point to uneven tidal heating, the process by which energy from rotation and orbit deform a planets outer crust. Others argue that lopsided bombardment by asteroids and comets explain our Moons Janus-faced exterior.