Moon Origin – Fission Theory (67)

Introduction

This is the third of the Moon Origin posts. This post explains the Fission Theory, which at the moment in scientific circles, has some validity but not enough to be considered a main contender.

The following excerpt comes from the book “Modern Mysteries of the Moon” by Vincent S. Foster.

The Fission Theory

“This is the idea that an ancient, rapidly spinning Earth expelled a piece of its mass. This theory was proposed by George Darwin (son of the famous biologist Charles Darwin) in the 1800s and retained some popularity until Apollo. The Austrian geologist Otto Ampherer in 1925 also suggested that the emerging Moon was cause for continental drift.

It was proposed that the Pacific Ocean represented the scar of this event. However, today it is known that the oceanic crust that makes up this ocean basin is relatively young, about 200 million years old or less, whereas the Moon is much older. However, the assumption that the Pacific is not the result of lunar creation does not disprove the fission hypothesis. This hypothesis also cannot account for the angular momentum of the Earth-Moon system, which is the gravitational torque between the Moon and the tidal bulge of Earth that causes the Moon to be constantly shifted to a slightly higher orbit and Earth to be decelerated in its rotation (Fig. 3.2 ).”

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Moon Origin – Capture Theory (66)

Introduction

This is the second of the Moon Origin posts. This post explains the Capture Theory, which at the moment in scientific circles, is popular but not as popular as the Giant Impact Theory. This theory just like the Giant Impact Theory has some holes. These holes are covered in this post.

The following excerpt comes from the book “Modern Mysteries of the Moon” by Vincent S. Foster.

The Capture Theory

“This hypothesis states that Earth captured the Moon. This was popular until the 1980s. Some things in favor of this model include the Moon’s size, orbit, and tidal locking. One problem is understanding the capture mechanism. A close encounter with Earth typically results in either collision or altered trajectories. For this hypothesis to work, the primitive Earth would had to have had an extended atmosphere around it, which would have been able to slow the movement of the Moon before it could escape. That may also explain the irregular satellite orbits of Jupiter and Saturn.

In addition, this hypothesis has difficulty explaining the identical oxygen isotope ratios of Earth and the Moon.”

End (66).

Moon Origin – Giant Impact Hypothesis - GIH (65)

Introduction

This is the first of the Moon Origin posts. This post explains the Giant Impact Theory, which at the moment in scientific circles, is the theory that it is most favoured. It is worth noting that this theory has some holes, that this there aspects about the Moon that this theory can not account for.

The following excerpt comes from the book “Modern Mysteries of the Moon” by Vincent S. Foster.

Giant Impact Hypothesis (GIH)

“The collision of two protoplanetary bodies during the early accretional period of Solar System evolution is the most widely accepted explanation for the origin of the Moon. This theory became popular in 1984. It satisfies the orbital conditions of Earth and the Moon and can account for the relatively small metallic core of the Moon. Collisions between planetesimals are now recognized to lead to the growth of planetary bodies. In this framework it is inevitable that large impacts will sometimes occur when the planets are nearly formed. The theory is thought to have originated in the 1940s with Reginald Aldworth Daly, head of the geology department at Harvard (Fig. 3.1 )

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The colliding body is called Theia , the mother of Selene , the Moon goddess in Greek mythology. The hypothesis requires a collision between a body about 90 % the present size of Earth, and another the diameter of Mars (half of the terrestrial radius and a tenth of its mass). This size ratio is needed in order for the resulting system to possess sufficient angular momentum to match the current orbital configuration. Such an impact would have put enough material in orbit around Earth that could accumulate and eventually form the Moon.

Computer simulations show a need for a glancing blow, which would cause a portion of the colliding body to form a long arm of material that then would shear off. The asymmetrical shape of Earth following the collision would then cause this material to settle into an orbit around the main mass. The energy produced by this collision would have been impressive: trillions of tons of material would have been vaporized and melted. The temperature would have risen to 10,000 °C (18,000 °F).

The relatively small iron core of the Moon is explained by Theia ’s core accreting into Earth’s. The lack of volatiles in the lunar samples is also explained in part by the energy of the collision. The energy liberated during the re-accretion of material would have been sufficient to melt a large portion of the Moon, leading to the generation of a magma ocean.

The newly formed Moon orbited 90 % closer than it does today. It became tidally locked with Earth, where one side continually FIG. 3.1 The giant impact theory suggested that growing smaller planetary body (Mars-sized protoplanet) hit Earth about 4.5 billion years ago, blowing out rocky debris that was captured into orbit around Earth and coalesced into the Moon. NASA illustration  faces toward Earth. The geology of the Moon has since become more independent of Earth. Although this hypothesis explains many aspects of the Earth-Moon system, there are still unresolved problems with it, such as why the Moon’s volatile elements were not depleted as expected from such an energetic impact.

Comparisons of lunar and Earth isotopes is another issue. In 2011, the most precise measurement yet of the isotopic signatures of lunar rocks was published. Surprisingly, it showed that the Apollo lunar samples carried an isotopic signature identical to Earth rocks, but different from other Solar System bodies. Since most of the material that went into orbit to form the Moon was thought to come from Theia , this observation was unexpected. In 2007, researchers from Caltech found that the likelihood of Theia having an identical isotopic signature to Earth was very small (<1 %).

An analysis of titanium isotopes in Apollo lunar samples in 2012 revealed that the Moon has the same composition as Earth, which conflicts with the Moon forming far from Earth’s orbit. To help explain problems with this, a new theory was published by R. M. Canup in late 2012 which posits that two bodies five times the size of Mars collided, then re-collided, forming a large disc of debris that eventually formed Earth and the Moon.

Released at the same time was another study on the depletion of zinc isotopes on the Moon, which supported the giant impact origin for Earth and the Moon. In 2013, a study was released indicating that water in lunar magma was ‘indistinguishable’ from carbonaceous chondrites and nearly the same as Earth’s, based on the composition of isotopes. Another challenge was issued September 2013, with a growing sense that lunar origins are much more complicated than can be fully explained by the GIH theory.”

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Moon Origin (64)

Introduction

In the next series of five posts or so I plan to present the various leading theories to explain how the Moon came to be.

This post though is only an introduction to the current status of the Moon origin theories.

The following excerpt outlining the current status of the Moon origin theories comes from the book “Modern Mysteries of the Moon” by Vincent S. Foster.

Excerpt

“Scientists have offered several major theories to account for the origin of the Moon. All have drawbacks, but the favored theory that emerged from the Apollo missions was the Giant Impact Hypothesis (sometimes called the Big Splat ). This states that our Moon was created by a collision between Earth and a Mars-sized object some 4.5 billion years ago.

There are a number of variations and alternatives, including captured body, fission, formed together (condensation theory), planetesimal collisions (formed from asteroid-like bodies), and collision theories. All of the theories have been challenged, and none satisfy all questions.

NASA scientist Dr. Robin Brett sums it up best: “It seems much easier to explain the nonexistence of the Moon than its existence.””

Conclusion

There you have it, a valid theory explaining the origin of the Moon has not been settled upon yet, leaving the Moon’s presence still an unsolved mystery.

To esotericism though the origin of the Moon is very definite, and still to me this seems to be much more viable. That of which the Moon actually predates the Earth.

End (64).

Craters on the Moon – Ancient Volcanoes or Impacts (63)

Introduction

The following excerpts from “Modern Mysteries of the Moon” by Vincent S. Foster explains the process of how the large craters on the Moon were discovered to be due to impact rather than the result of ancient dried volcanoes. This discovery actually shone new light onto the topic of how the Moon has developed through time.

Moon Craters Originally Thought to be Volcanoes

Until the late 1800s, most astronomers thought that volcanism formed the craters of the Moon. In the 1870s, the English astronomer Richard A. Proctor proposed correctly that the craters resulted from the collision of solid objects with the Moon. But at first, few scientists accepted Proctor’s proposal. Most astronomers thought that the Moon’s craters must be volcanic in origin because no one had yet described a crater on Earth as an impact crater, but scientists had found dozens of obviously volcanic craters (Fig. 1.4 ).

Idea of Impact Craters Proposed by Gilbert

“In 1892, the American geologist Grove Karl Gilbert argued that most lunar craters were impact craters. He based his arguments on the large size of some of the craters. Those included the basins, which he was the first to recognize as huge craters. Gilbert also noted that lunar craters have only the most general resemblance to calderas (large volcanic craters) on Earth. Both lunar craters and calderas are large circular pits, but their structural details do not resemble each other in any way. In addition, Gilbert created small craters experimentally. He studied what happened when he dropped clay balls and shot bullets into clay and sand targets.

Gilbert was the first to recognize that the circular Mare Imbrium was the site of a gigantic impact. By examining photographs, Gilbert also determined which nearby craters formed before and after that event. For example, a crater that is partially covered by ejecta from the Imbrium impact formed before the impact. A crater within the mare formed after the impact.”

Relevance to Lunar Evolution

“Gilbert suggested that scientists could determine the relative age of surface features by studying the ejecta of the Imbrium impact. That suggestion was the key to unraveling the history of the Moon. Gilbert recognized that the Moon is a complex body that was built up by innumerable impacts over a long period.

In his book The Face of the Moon (1949), the American astronomer and physicist Ralph B. Baldwin further described lunar evolution. He noted the similarity in form between craters on the Moon and bomb craters created during World War II (1939–1945) and concluded that lunar craters form by impact.

Baldwin did not say that every lunar feature originated with an impact. He stated correctly that the maria are solidified flows of basalt lava, similar to flood lava plateaus on Earth. Finally, independently of Gilbert, he concluded that all circular maria are actually huge impact craters that later filled with lava.”

Conclusion

The Moon has been orbiting in space for a long time and has actually received many impacts. However by studying the lunar craters scientists have been able to gleam information about how the various layers of the Moon’s surface has formed.

End (63).