© Lloyd, Charles Chandler

 

MOON ORIGIN

"The Moon itself is an example of the product of a collisional erosion event involving the Earth during the final stages of its accretion. The mass of the Moon is 1.8% of the mass of the Earth's mantle."12

"The Moon is believed to have formed largely from impactor material following the collision between the Earth and Theia."14

"Magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness" in the case of the Moon.5

In contrast to the Earth, the Moon lacks a large iron core.3

"In order to produce 13.6% by weight FeO in the Moon's mantle, approximately 70% of the Moon would have to be derived from Theia. This value is very similar to the results derived from numerical simulations of the Moon-forming impact."14

"The most favorable conditions for producing a sufficiently massive and iron-depleted protolunar disk involve collisions with an impact angle near 45 degrees and an impactor velocity at... less than 4 km/sec. For a total mass and angular momentum near to that of the current Earth-Moon system, such impacts typically place about a lunar mass of material into orbits exterior to the Roche limit, with the orbiting material composed of 10 to 30% by mass vapor. In all cases, the vast majority of the orbiting material originates from the impactor."3

"The impactor material that ends up in orbit is primarily that portion of the object that was heated the least, having avoided direct collision with the Earth."3

Among likely scenarios, "those that leave the Earth > 95% accreted after the Moon-forming impact are favored here, implying a giant impactor mass between 0.11 and 0.14 Earth masses."3

"The simplest explanation for the Moon's unusual compositional characteristics is that it is the result of an impact that occurred near the very end of terrestrial accretion."3

Portions of the Moon's crust are strongly magnetized, but the origin of the fields that magnetized the crust is uncertain. One proposed solution is that "dynamo action comes from impact-induced changes in the Moon's rotation rate. Basin forming impact events are energetic enough to have unlocked the Moon from synchronous rotation, and we demonstrate that the subsequent large-scale fluid flows in the core, excited by the tidal distortion of the core-mantle boundary, could have powered a lunar dynamo. Predicted surface magnetic field strengths are on the order of several microteslas, consistent with palaeomagnetic measurements, and the duration of these fields is sufficient to explain the central magnetic anomalies associated with several large impact basins."11