The Moon in one important context is a lot like my wife. The more I study Kathy, the more I discover how amazingly designed she is to help me become an effective servant of the Creator of the universe. The more astronomers and physicists research the Moon, the more they discover how marvelously designed the Moon is, and how it makes the ability of Earth to support billions of human beings possible—where many billions of those humans can respond to the Creator's offer of redemption from evil and suffering.
In my book Improbable Planet, I tell the story of how models for the origin and subsequent development of the Moon have increasingly progressed in their capacity to explain in ever greater detail and in ever greater comprehensive scope the present characteristics of both the Moon and Earth.1 This story reveals that as astronomers have developed more detailed and refined models for the origin of the Moon, the established complexity and fine-tuning in the origin and evolution of the Earth-Moon system needed to make human life possible on Earth has accumulated at an exponential rate.
Is the Formation of the Moon a Result of Coincidences?
The recognition of exponentially accumulating evidence for complexity and fine-tuning in Moon-formation models prompted a number of philosophical comments from the modelers. In a 2013 issue of Nature, a Moon-formation modeler Robin Canup wrote, "Current theories on the formation of the Moon owe too much to cosmic coincidences."2 In the same issue, Earth scientist Tim Elliott lamented, "The sequence of conditions that currently seems necessary in these revised versions of lunar formation have led to philosophical disquiet."3
The increasing list of cosmic "coincidences" is only disquieting, however, for researchers insisting on non-theistic interpretations of the Earth-Moon system. In 2014 and 2015, more sophisticated models offering yet greater explanatory scope added to the list of cosmic coincidences, and for non-theists, even more philosophical disquiet.4 Now, as Thanksgiving Day is just a few days away, a new research study5 by four leading planetary scientists on the Moon-formation event gives us several more reasons to thank God for the way he designed the Moon and Earth so that we can not only survive, but thrive on our beautiful and bountiful planet.
New Theories on the Formation of the Moon
All the leading theories for the Moon's origin explain why the Moon is so extremely large relative to the size of its host planet (it is 50 times larger than the next largest moon) and why the Moon has such a tiny iron core. All these models suggest that the ancient hypothetical planet Theia, which is almost as large as the primordial Earth, collided with the primordial Earth when it was a little less than 100 million years old.6 All these models predict that the initial Earth-Moon system will possess a high measure of angular momentum. The remaining challenge, then, is to explain how the initially high-angular-momentum Earth-Moon system evolved to its current low-angular-momentum state.
Two models successfully explained the loss of the Earth-Moon system's angular momentum.7 These models appealed to "evection resonance" to solve the angular momentum loss problem. However, the tidal parameters for Earth and the Moon to allow for evection resonance to sufficiently reduce angular momentum proved highly restrictive. Furthermore, it was not clear that evection resonance solved the problem of the origin of the Moon's orbital inclination.
The four planetary scientists in the new research study used an analytical model in which they quantified the effect of obliquity tides within the Moon. (Obliquity refers to the rotation axis tilt.) They showed that early in the Moon's evolution, gravitational perturbations from the Sun enlarged the eccentricity of the Moon's orbit. This enhanced eccentricity removed angular momentum from the Moon's orbit and transferred it to Earth's orbit. Earth's tides in turn transferred angular momentum from the Earth's rotation to the Moon's orbit.
The team of four showed that if Earth arising from the collision event begins with a high obliquity and a rapid rotation rate, the Moon's tidal evolution produces the Moon's present orbit, including the inclination of the Moon's orbit and the angular momentum of the Earth-Moon system.
The team of four concluded that after the Moon-forming collision event, Earth began with an obliquity of 70 degrees and a rotation rate of 2.5 hours. This result is gratifying, since the best Moon-formation models all predict that the collision event yields a high obliquity and a rapid rotation rate for Earth.
Research Reveals More Fine-Tuning of the Moon
The team's model stands as the only Moon-formation model that explains the origin of the Moon's large past orbital inclination that was subsequently reduced to just 5 degrees by strong obliquity tides. Though the team's paper never mentions fine-tuning, their research implies yet more fine-tuning in the Moon's properties to make human civilization possible. The Moon's orbital evolution throughout its history must be exquisitely fine-tuned to ensure that the Moon's tidal interaction with Earth slows down Earth's rotation rate from about 2.5 hours to its present 24 hours.
A rotation rate of 24 hours is optimal and necessary for Earth to support billions of human beings where those billions of humans sustain a global high-technology civilization. Such civilization is needed for billions of humans to hear and respond to the gospel message and become disciples of Christ. That civilization also requires that Earth's 24-hour rotation rate occur at the same time the Sun radiates minimal ultraviolet and x-ray radiation, manifests the least intense and least frequent flaring events, and manifests extreme luminosity stability.
Additional fine-tuning arises from the manner in which the evolution of the Moon's physical features and its orbit makes possible the advance of knowledge in the physical sciences. The Moon and its orbit has evolved to where presently the angular size of the Moon in Earth's sky is identical to the angular size of the Sun. This identity makes possible perfect solar eclipses. Thanks to perfect solar eclipses, astronomers and physicists launched the discipline of coronal physics, tested and affirmed the theory of general relativity, and deepened their understanding of stellar atmospheres.
Only a carefully fine-tuned orbital history of the Moon from its time of formation to the present moment guarantees that all these outcomes will be in place. Indeed, we have many more reasons this coming Thanksgiving Day and every day to thank God for the exquisite way he designed the Moon-forming event and the Moon's subsequent development.