The Third Age of Understanding the Moon has Arrived — Are we Ready?
The Moon is our most familiar companion in the night sky, bathing us with light and comfort during the darkest hours. Some of our oldest myths and legends stem from an innate need to understand the majesty and splendor of our planetary neighbor.
Worship of the Moon is prevalent throughout the history of the world, and marked the first age of attempting to unravel the mysteries of the Moon. The vast majority of ancient people did not have the tools of science and reasoning to explain natural phenomenon, and turned to gods, goddesses, and magic to describe their world. Attempts to understand the Moon fell to stories of god-like beings and superstition.
Although most deities associated with the Moon were female, this was not always the case. Ancient Greeks worshiped the Goddess Selene, followed by her Roman counterpart, Luna. The moon god Mani ruled the night skies for Germanic tribes, and the Japanese gave thanks to their moon god, Tsukuyomi. Across their western waters, people in China recognized Chang’e, a name which would become associated with the birth of our third great age of understanding the nature of our planetary companion.
Science Sheds Light on the Second Age of the Moon
When we first glanced upon the surface of the moon with the eyes of science centuries ago, the second age of our understanding of the Moon was launched. Generations of astronomers and mathematicians enriched the world with understanding, developing a tremendous wealth of knowledge about our closest planetary companion. This age reached its zenith with the landing of 12 people on the lunar surface, an accomplishment which has, not yet, been repeated.
With good reason, however, researchers of the era believed the Moon was a dry body, sitting devoid of any geological activity. Even when the Apollo astronauts returned to Earth bearing moon rocks, traces of water detected in the samples were chalked up to terrestrial contamination from a leaky container.
The Moon, once magical, was thought to be a dead and lifeless (if rather large) rock in space. The best data at the time showed what it could, but the next age of understanding the Moon would require technological advances not available in the era of Atari 2600’s and disco pants.
The Rise of the Third Age
Today, we are living at the beginning of a third great age in our understanding of the Moon. Our planetary companion is now a world we experience as changing and dynamic, encompassing an active mantle and experiencing moonquakes.
Ancient magma has been spotted on the far side of the moon, water ice has been detected near the poles, and water molecules may even form directly on the lunar surface.
The Chinese space agency landed the Chang’e-4 (CE-4) on the far side of the Moon in January 2019, making China the first nation to ever land a spacecraft on the far side of our planetary neighbor. Following touchdown, the spacecraft released the Yutu-2 rover to explore the South Pole-Aitken (SPA) impact basin, stretching 2,500 kilometers (1,500 miles) in diameter, roughly equal in size to the distance between Maine and Florida in the United States.
The Prequel to The Moon
One generally-accepted theory postulates that the lunar surface was likely once covered in a layer of magma. As this ocean of molten rock cooled, heavier components (such as olivine and pyroxene) sank, while lighter basalt rose, forming the outer crust of the Moon. As asteroids and various bodies struck the Moon, material trapped under the crust was brought up to the surface, a process which would normally enrich concentrations of olivine in the lunar crust.
The Visible and Near Infrared Spectrometer (VNIS)7 onboard the Yutu-2 revealed the presence of low-calcium (ortho)pyroxene and olivine, materials which may have formed within the mantle of the Moon, although traces of olivine within the basin were rare.
Concentrations of the mineral was more common in material kicked up during deeper impacts, suggesting layers of rock under the crust of the Moon may be composed of nearly-equal quantities of olivine and pyroxene. Here on Earth, olivine dominates, marking a significant — and newly-understood — geological difference between the Moon and our home planet.
“Understanding the composition of the lunar mantel is critical for testing whether a magma ocean ever existed, as postulated. It also helps advance our understanding of the thermal and magmatic evolution of the moon,” said LI Chunlai of the National Astronomical Observatories of Chinese Academy of Sciences (NAOC).
Analysis of the inner layers of the Moon and the detection of moonquakes reveal that our planetary companion, once thought to be geologically dead, also still retains a molten core. As heat left over from the formation of the Moon escapes to space, contraction of the Moon results in a wrinkling of the lunar crust, a previously-unknown effect that astronomers have only recently witnessed for the first time.
“The discovery of young thrust faults on the Moon is evidence of recent tectonic activity, but how recent is unknown. Seismometers at four Apollo landing sites recorded 28 shallow moonquakes between 1969 and 1977. Some of these shallow quakes could be associated with activity on the young faults,” researchers report in Nature Geoscience.
Still, Bring Water with You. We’re in a Desert.
The Moon is drier than any desert on Earth, but our planetary companion is not completely devoid of water. New research suggests that every ton of lunar crust contains around 32 ounces of water (roughly equivalent to one liter of water per 900 kilograms of lunar crust).
The presence of water or hydroxyl (chemically-bonded molecules containing hydrogen and oxygen) has been detected by India’s first Moon probe, Chandrayaan-1, as well as NASA’s Cassini and Deep Impact spacecraft. Cassini examined the Moon on its way to Saturn, and Deep Impact made a lunar study on its way to its primary target, the comet 103P/Hartley 2.
“The Deep Impact observations of the Moon not only unequivocally confirm the presence of [water/hydroxyl] on the lunar surface, but also reveal that the entire lunar surface is hydrated during at least some portion of the lunar day,” researchers wrote in a study detailing results from the Deep Impact study.
While some water comes to the Moon via impacts with comets and icy bodies, the solar wind may also create water directly on the lunar surface.
When positively-charged protons in the solar wind impact the lunar surface, they can react with negatively-charged electrons in the lunar crust, resulting in the release of hydrogen atoms. Meeting oxygen atoms in the silica of the lunar crust, they can form hydroxyl, and the addition of a second hydrogen atoms produces water.
“We think of water as this special, magical compound. But here’s what’s amazing: every rock has the potential to make water, especially after being irradiated by the solar wind,” said William Farrell, a plasma physicist at NASA’s Goddard Space Flight Center.
Molecules of water can move around from one area to another, as heating from the Sun drives molecules of water from areas where sunlight strikes to shadowed regions. As the Moon rotates once per month, sunlight and heat comes and retreats from nearly every location on the lunar surface. The exception to this cycle of a slow-motion day and night are some deep craters, sitting at the poles, which remain eternally in shadow. Through this constant heating and retreat to the shadow over most of the Moon, water migrates from one area to another around the crust, and water ice may slowly build up within craters where sunlight never strikes.
“If the water molecules are as mobile as we think they are — even a fraction of them — they provide a mechanism for getting water to those permanently shadowed craters. This opens a whole new avenue [of lunar research], but we have to understand the physics of it to utilize it,” said Carle Pieters, planetary geologist at Brown University.
The Baby Pictures of Earth Must have been Adorable
Recent discoveries of the nature of the Moon lend further evidence to the theory that our lunar companion was formed billions of years ago, when the cooling Earth experienced an impact with a Mars-sized body called Theia. This event, which took place roughly 4.5 billion years ago, shattered Theia, before debris from this impactor coalesced to form the Moon.
Analysis of this theoretical impact suggested that the Moon would mostly be composed of material from Theia. However, samples brought to Earth from the Moon by the astronauts of Apollo showed the lunar surface was similar to that found in the crust of our own planet. The answer to that conundrum may come from recent computer simulations suggesting that if the Earth were still largely molten when it was impacted by a hard, cold Theia, the greatest impact our world ever experienced would have resulted in a moon much like the one we see today.
We are lucky enough to live in a time when we are seeing such great advances in our understanding of the Moon. A new zeitgeist of the Moon brings the logic and scientific method of the second age together with the life and awe of the first era.
As astronomers and other researchers learn more about the active nature of the Moon, our planetary companion beckons us back once more. Five decades after Apollo, the lunar surface may soon, once again, feel the imprint of human footsteps.
This time, our visit may be permanent, and stepping off our home world for good, like a teenager leaving the safety of their parent’s house, will change our species forever. We will no longer be in danger of extinction from any single, planet-wide disaster. Traditional nations and borders will likely disappear, and even notions of race will likely become meaningless.
In the coming decades, the rule of governments could be greatly weakened for colonists on the Moon, Mars, and in space stations positioned around the Solar System. Much like notions of the wild west, opportunity could mix with very real dangers.
We are now facing a new time in the history of the human race, brought about by the third age of understanding our planetary companion. The next question is who gets to the Moon first.