Lunar Capture

Origins of the Earth's Moon

Evidence of a Secondary Heating on Earth

The idea that the Earth and Moon may have once been quite close together is not a new one. Speculation was rampant in the pre-Apollo period about a possible close approach and tidal interaction between the Moon and Earth, as an explanation for the formation of the lunar maria. This model was the dominant model of lunar formation during the days of the Apollo missions. In the classic capture model the Moon is an independent planet in a heliocentric orbit. The biggest difficulty with the classic capture model is the problem of how to redirect the Moon from a Sun centered orbit to an Earth centered orbit.

The Moon is a relatively large mass compared to the Earth and thus it would not be easily slowed, redirected and captured. In order to facilitate capture and bring the Moon into an Earth centered orbit it was thought that some of the energy of lunar motion about the Sun would need to be dissipated to slow and prepare the Moon for capture. This energy dissipation would be manifested in a physical heating of the Earth-Moon system. Classic capture models have this event lasting a short time, one hundred to one thousand years. It was thought that evidence of this heating event should be found in the geologic history of the Earth.

Because it was thought at the time that the heating event would be so destructive that life could not possibly have survived, the search for this heating event was centered on the very earliest time of planetary formation. Though several geologic events were potentially identified which could have been evidence of tidal heating it was difficult to prove such an ancient association.

It was not until much later that evidence from Jupiter’s moon Io showed that tidal heating, though powerful, was not the destructive planet destroying phenomena once imagined. The constraint of the isotopically dated ancient lunar maria however, continued to prevent the search for evidence of a more recent tidal heating event in the Earth-Moon system. The release of the ancient lunar maria constraint, proposed in the Close Approach Lunar Model, allows us to ask; “Could a close approach of the Moon be the cause of the Permian extinction, the greatest extinction of all time?”