Do lunar mass concentrations (mascons) create the gravitational force which causes the near side of Moon to be "tidally locked" so that it always faces toward Earth? see https://www.sciencedaily.com/releases/2013/05/130530142009.htm Yes, I understand the same side of Moon always faces Earth is because it rotates at the same rate as its revolution, but why? The rate of lunar revolution varies, so why does the rate of rotation vary at the same rate? Indeed, the distance between Earth and Moon is increasing due to Earth's tides. Why then does rotation remain locked with revolution? There has to be another force involved (I postulate: mascon gravity).
Mascons are located in the Imbrium, Serenitatis, Crisium and Orientale basins (all near side). The far side of the moon has few areas that qualify as mascons. http://planetary.s3.amazonaws.com/assets/images/3-moon/20121211_moon_grail_gravity_bouguer_PIA16578.jpg This shifts Moon's center of gravity towards the near side. There is a slight variation in the face presented by the moon (8 degrees each side) by the moon's libration, so we see more than just the near 180 degrees. The moon's shape is slightly oblong, the tidal bulge of the moon caused by Earth's gravitational tug and less because of its own (27.3-day) rotational motion.