Moon's mountains made by slo-mo crash: study

The Moon's 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.... At least one such mini-moon, about a third the diameter of the one we see today, could have been suspended between the gravitational pulls of the Moon and Earth for tens of millions of years, they calculated. Eventually, however, it would have lost its moorings and crashed into the Moon.... "According to our simulations, a large 'moon-to-Moon' size ratio and a subsonic impact velocity lead to an accretionary pile rather than a crater," Jutzi and Asphaug concluded. This scenario would also help explain why the farside's crust is so much thicker, and why certain minerals are concentrated there