Lunar Capture

Origins of the Earth's Moon

Close Approach Lunar Model

The past evolution of the Moon’s orbit has interested science since at least George Darwin’s study of rotating viscous spheres in the late 19th century.  It is typically thought that the Moon has been steadily retreating from the Earth for the past four plus billion years.  Strangely though, today when the Moon’s current rate of retreat is calculated backwards it is found that the Moon approaches the Earth some 1.8 billion years ago.  It is the investigation of this question which has ultimately led to the hypothesis of a close lunar approach in the history of the Earth-Moon system.

What might a lunar approach have looked like?

The Close Approach Lunar Model is based on the hypothesis of an intermediate or secondary “close approach” of the Moon to the Earth.  It proposes that the Moon retreated from the Earth initially, as in classic origin models, but that a significant intermediary “regression event” altered its course, causing “The Moon” to spiral or fall back in towards the Earth.  In other words, the Moon was presumably slowed in its original orbit by tidal exchange with the Earth, and subsequently began to spiral in towards the Earth.  But today we clearly see that the Moon is retreating from the Earth.  Rather than “crashing” into the Earth during this regression event, the Moon experienced just a short high energy close approach to the Earth.  Dynamically speaking the Moon bounced off the Earth.  This close temporary Earth orbit of the Moon then evolved out to where we see the Moon today.

The current lunar orbit, the model proposes, is thus the result of the close approach dynamics of this eviction event, not the dynamics of the “origin” of the Earth-Moon system as classic origin models assume.  Though the dynamics of this event have the signature of a classic capture event, it is better described as a secondary capture and/or heating event in the evolution of the Earth-Moon system.

The Close Approach Lunar Model

Both the Moon and Earth underwent significant change at what is recognized on Earth as the Permian Triassic (P-T) boundary. A Close Approach Lunar model hypothesizes that a close approach brought the Moon near enough to the Earth to produce a secondary (tidal) heating event in the Earth-Moon system which can answer a multitude of the unexplained geophysical questions that exist in the Earth-Moon system.

Io VolcanoSuch an event would have provided the heat which initiated the formation of the lunar mare and Earth’s continental flood basalts beginning with the Siberian traps. This tidal heating correlated with the geologic history of Earth and impacts our understanding of plate tectonics and volcanism since the time known on Earth as the Permian.

The closer Moon would have caused mixing of the anoxic benthic layer with the oxygenated surface layer, of Earth’s Permian ocean, thus explaining a unique feature of the Permian marine extinction. Dissipation would have energized Earth’s tectonic system. The higher energy tectonic system would initiate the breakup of Pangaea and the spreading of the modern continents. The developing tectonic system would ultimately lead to the build up of atmospheric pressure during the Jurassic. This high density atmosphere allowed the dinosaurs to grow to their great size. As the tidal heating waned with the retreat of the Moon, the atmosphere thinned as less gas was being produced through volcanic activity associated with the energized tectonic system. During the Cretaceous period which ended with the disappearance of the dinosaur the beginning of seasonality can be seen in Earth’s climatic evolution for the first time.

Earth and MoonThe Moon has been slowly retreating from the Earth ever since the P-T boundary and the energy has been slowly dissipating. The seasonal Earth of today is a product of past tidal interactions between the Earth and Moon. Our modern Earth is a vital and dynamic body still reeling from a heating event that occurred in the not so distant past.