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The Close Approach - A New Lunar Model

A Lunar Model

  • The Calm
  • Tidal Heating
  • Great Dying
  • Siberian Traps
  • Dinosaur Rise & Fall
  • Pangean Breakup
  • Global Warming
    • Seasonality
  • Lunar Origins
    • Apollo History

Lunar Origins

Lunar Origin Models

The study of the moon and lunar origin has fascinated man since the time of Stonehenge. Where did the Moon come from? People from many scientific fields have weighed in on the subject through the ages. It was hoped that the Apollo missions would finally answer this long standing mystery. But alas the failure to confirm a lunar origin model may have been the greatest scientific disappointment of the Apollo effort. There are four major categories of lunar origin models: the binary model, fission model, collision model, and capture model.Lunar Origin: The moon and planets originated out of nebula cloud

  • The Binary Model
  • The Fission Model
  • The Collision Model
  • The Capture Model

The Binary Model

Accretion ModelThe binary model, in some respects, is the simplest and least problematic lunar origin model and thus is usually considered the default model. Binary formation is what would be “expected” in standard solar system formation models, with the moon forming as part of the earth’s nebular cloud. Satellites which originate in this manner are called regular satellites. Satellites which have unusual orbits, typified by a moon which orbits its planet in a direction opposite to the planet’s direction of rotation or “backwards,” are considered irregular satellites. The binary model does not require any “special circumstance” for the formation of the moon; the earth and moon simply formed together out of the same cloud of primordial material. Accretion Model shows the moon formingThe situation of the earth-moon system however, is generally believed to be unique. This is why the other three models (the fission model, collision model, and capture model) have been developed to answer some of these unique conditions of the earth-moon system.

The Fission Model

Lunar Origin Fission ModelThe fission model was the model often taught in grade school during the Apollo era. Interestingly, at the time of Apollo, it was still taught that the Pacific Ocean was formed by the fission of the moon from the earth’s crust. The model of plate tectonics was still a hypothesis while man was walking on the moon.

The fission model was first presented by George Darwin, the son of Charles Darwin. This was really the first scientific and comprehensive model developed to explain the origin of the moon. Darwin’s work was done on rapidly spinning viscous bodies. He calculated that the earth would have about a 2.5 hour day in order to have the centrifugal force to spin the moon off. It was later determined that the fission model is not dynamically possible for two major reasons. First, the bulge at the earth’s equator which ultimately would form, and be flung off, would cause instability in the earth’s spin leading to a slowing of the earth’s spin. Fission Lunar Origin Model from a rapidly rotating earthThis negative feedback would dampen the spin of the earth before it could reach a fission speed. Second, it is not believed that the earth could slow from a 2.5 hour day to a 24 hour day in the 4+ billion years which have elapsed since lunar formation. The classic fission model seems not to be possible but many of its consequences have been reborn in the newer “collision model.”

The Collision Model

Big Splat Collision Model with vibrant colorsThe collision model, developed in the 1980s, originally had the same main objective as the fission model; to explain the observed similarity in density of the earth’s outer mantle and the moon. The original idea was that the moon formed as a result of a collision between the proto-earth and another free roaming planetary body in the very early days of the solar system.

The similarity in the density between the moon and the earth’s mantle had long attracted scientific interest. In the beginning it was thought that the collision model would account for this similarity in density, just as it had been thought that the fission of the earth’s mantle would account for the similarity. Ironically, further investigation led to the understanding that in the case of collision, the moon would actually be composed primarily of the impacting proto-moon, not the proto-earth material.

A strong selling point of the collision model is that computer simulation of a proto-moon impact into the earth can produce the desirable outcome of creation of a moon; though these simulations are quite simple approximations of reality.

Glowing binary pairA potential problem with the collision model results from the finding that in order to generate a Moon such as ours in a collision origin, the initial proto-spin of the earth must have been around 2.5 hours. The rapid spin rate would have to have slowed to our current 24 hour day, and this may be difficult to achieve. This same result was a blow to Darwin’s fission model and must be dealt with in proving the collision model.

Another interesting piece of evidence is that the moon may have water on it.  The moon, it had been thought, lacked any water bearing minerals.  This Apollo age belief seemed at odds with the collision model given the aqueous nature of Earth, with its modern oceans.  How a dry moon formed from a wet planet was a continuing question.  But recent evidence now seems to suggest that water may exist on the moon.

The Capture Model

Lunar Origin Capture Model diagramThe observation that our moon is a rather unusual partner for the earth was the strongest selling point for the capture model. The moon’s unusually large size, its non-equatorial orbit, and its tidally locked orientation all suggested a possible capture origin. (NASA’S Evolution of the Solar System)

The capture model was a favorite model during the Apollo age. The greatest difficulty with the capture model is the dynamics of the capture event itself. This event is typically imagined as a freely moving moon nearing the earth and the gravitational power of the earth, literally slowing the moon to the point that it becomes permanently “captured” into a geocentric or earth centered orbit. The difficulty with this proposition is primarily the relative size of the moon compared with the earth. The kinetic energy of the moon, which would be required to be dissipated, in order to slow the moon down and facilitate a captured moon, is immense. It is felt that the capture event window would be too brief to allow this amount of energy to be dissipated from the lunar motion.

One solution to this slowing problem was what is called the gas drag model. In this capture variation it was postulated that the early earth was enveloped in a thick gas cloud which would contribute to the slowing of the moon as it approached the earth. Even with this added dissipation mechanism, capture was still found to be too energetic of a process to be very likely.

It is important to recognize that during the Apollo age the concept of tidal heating in the solar system was just beginning to be understood. It had previously been postulated that perhaps both the lunar flood basalts and earth’s own flood basalts had been caused by a capture event. But the whole understanding of how this heating worked was still very theoretical. Had there been recognition of tidal heating’s potential and the quantities of heat needed to make capture work, the capture model may have been looked at more closely.

Another major problem with the capture model was thought to be that oxygen isotope evidence proved a similar place of origin for the earth-moon system in the solar nebula. This was seen as conclusive evidence that the capture model was not the correct model. This oxygen isotope evidence has since been found to be unrelated to the origin argument. Thus what was once thought to be one of the few strikes against capture was later found not to be important.

The CALM

To be clear, a capture at the time of origin of the earth-moon system would have involved tidal heating.  However, this is an entirely different and unrelated event than the tidal heating described by this new model. The Close Approach Lunar Model (CALM) is a secondary heating event, which happened billions of years after the origin of the solar system and is independent of any lunar formation model.  The several models for the formation of the earth-moon system that have been carefully delineated by scientists over the past hundred years are all “origin” models. The model presented here, the Close Approach Lunar Model, is not a new “origin model” but instead is an insertion of an additional and much later “event” into the history of the earth-moon system. This close approach event could have followed any of the accepted origin models. This secondary close lunar approach event, however, has significantly contributed to the history of the earth-moon system. It will be shown that evidence for this event is wide spread on both the earth and moon.

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ABOUT LUNAR ORIGIN

Journey to Discovery

The CALM (Close Approach Lunar Model) takes us back to the dawn of the Apollo age and shows us where science took the wrong turn that changed Earth and lunar science, and left us with more questions than answers.

The intellectual buildup leading to the Apollo missions brought on some of the greatest engineering and scientific achievements of mankind. Scientific collaboration and speculation were at a fever pitch as the first manned excursions to the moon approached. It was thought that science was on the verge of the “big one” and that the Apollo missions would answer the question of how the earth-moon system came to be.

Alas, it was discovered that the situation was much more complex than ever imagined. Though the Apollo missions provided valuable scientific data, samples and knowledge, it was roundly agreed that Apollo failed to answer the most important question of all, “How did the earth-moon system come to be?” Interest in the moon as well as the questions of the origin of the earth and moon as a system, drifted off into the many labs and scientific facilities which handled and catalogued the material and information of the Apollo missions. NASA and the scientific community moved on to the space shuttle, space station, and interplanetary exploration, leaving our nearest neighbor to the backyard astronomer.

In reality a small cadre of lunar scientists still exists. The Lunar and Planetary Science Institute and its university partners promote and facilitate the continuing pursuit of lunar science.

Presented here is my model which is based on our current understanding of, “How did our earth-moon system come to be and how might the moon impact global climate today?”

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