# Mascon gravity causes tidal lock

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).

• There may already be an answer to this question in Astronomy SE. Check the tidal-locking and the tidal-forces tags there. – uhoh Mar 14 '18 at 18:32
• IANAexpert, but I believe that the cause of tidal locking is not related to mascons, but the final orientation of the locked body may be determined by the mascons. – Russell Borogove Mar 14 '18 at 20:39
• To explain a tidal lock, you need something other than gravitational forces alone. You need a process that converts the energy of rotation to energy of heat. That are the tidal forces squeezing the moon. Remaining locked happens when there is one revolution around the axis of the moon during one orbit. The tidal forces are zero then. No more acceleration or deceleration of rotation. – Uwe Mar 15 '18 at 14:45

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.

• You've asked a yes/no question: "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?" so an answer will need to address this. If you would like to change your question to "where are the Moon's mascons located to match your answer, then double check that it hasn't been answered already. – uhoh Mar 14 '18 at 19:11
• The Moon's center of mass is indeed shifted toward the Moon's near side, but that has little to do with the mascons. The primary reason is the far thicker crust on the far side of the Moon. – David Hammen Mar 15 '18 at 1:47