A little over a year ago, I came upon the idea that the eccentricity of Mercury's orbit around the sun creates a tremendously oscillatory solar gravitational force (essentially, massive "solar tides"), which ripped the tectonically dying (now tectonically dead) planet apart.* It also included an attempt to calculate the sun's gravitational lock upon Mercury (I wound up flubbing the calculations, but the fact of Mercury's day being two-thirds of her year, as opposed to the Moon's day being identical to her year, clearly means that the sun's gravitational lock upon Mercury is 2/3 her gravitational lock upon the moon). So, why is Mercury being ripped apart by the sun, when the moon isn't being ripped apart by the Earth or the Sun?* (Indeed, the moon has been in the process of escaping Earth's orbit (perhaps, eventually,to become an independent planet) ever since she was formed.)* *I accept the theory that the moon accreted from the ejecta of a collision between Earth and a Mars-sized planet, which means only the least dense crustal material would have remained in orbit rather than crashing back into Earth, meaning the moon was never tectonically active, and is, today, a unitary, solid body (essentially, a big puff-ball in the sky).* (This further explains the moon's lack of mass relative to the smaller Mercury.)* Thus, it has never had any layers to peel apart. A couple of years ago I watched a show on National Geographic called "Journey to the edge of the Universe", in which was mentioned the fact that the planet Mercury, which is a ball of solid iron with a relatively thin coating of rock, was obviously the core of what had once been a much larger planet.* The show said that Mercury must have collided with another planet to produce this result, but I posit an alternative theory: that, when the planet cooled to the point of tectonic death, its various layers separated, leaving the original crust and most of the mantle susceptible to being ripped apart by the immense solar tidal forces, and, eventually, torn off and pulled into the sun by solar gravitational attraction (in the manner of old plywood separating into its various layers). (I draw my facts for the following discussion from this webpage: http://www.universetoday.com/tag/planet-mercury/ .) Mercury has a volume of 0.056 Earths, and Mercury's enormous iron core is 0.42 Mercurys, whereas Earth's core is only 0.17 Earths. This means Mercury's core is equal to 0.02352 Earths, or 0.1383529 Earth cores.* This further means, if my assumptions are correct, that Mercury lost 86.16471% of its volume, whatever the event that caused the volume loss (which did not, in turn, cause equivalent loss of mass, as Mercury, being smaller than Earth's moon, has, proportionally, more than twice the gravitational attraction (i.e., in absolute terms, more than twice the mass of the larger Moon). I'm not here advocating that Mercury was totally tectonically dead at the time of the major volume-loss event (which event I theorize took place over an immense period of time (and may, in fact, be continuing, too slowly for humans to have observed since we gained the capability to observe the planets)).* In fact, evidence of lava flows on the current surface of Mercury conclusively proves quite the opposite.* I'm only arguing that Mercury had cooled and solidified to an extent sufficient to cause the effect I described (and I have no idea what point that may be!).* But, the omnipresence of impact craters confirm that the planet is currently tectonically dead. *** Please notice that my theory doesn't require any one-time event, but, rather, an event which has been ongoing for millions of years, and which may be still ongoing.