Being our nearest neighbor, the Moon has always found its way into the realms of human curiosity; its desolate beauty has been the source of fascination, inspiring a rich cultural and symbolic tradition. It is no wonder then that it was the first new world on which humans set foot, and the target of dozens of astronomical missions, aiming to explore its mysterious body.
These explorations, as well as satellite images and remote-sensing observations highlighted radical differences between its nature and that of Earth. In this issue in which we discuss the four elements of nature, let us investigate how different, or similar, they are on the surface of the Moon.
Earth
Looking at satellite images of the Moon’s surface, all we can see are grayish rocks and dust beds; they are very different in nature from their counterparts on Earth though. Most lunar rocks are igneous(1) while most Earth rocks are sedimentary(2); two common kinds of lunar rocks are basalts, rich in iron and titanium and found in lunar maria(3), and anorthosites, rich in aluminum, calcium and silicon, and found in highlands.
Similarly, lunar soils are different from “soil” as we know it, for there is no biological factor in their formation. They are basically derived from lunar rocks, yet, they contain some alien materials coming from celestial bodies crashing into the Moon’s surface. Lunar soils also encompass solar-wind-driven particles that get implanted in the outer layers of soil grains.
Space scientists are indulged in extensive studies of lunar rocks and soils because they are believed to hold clues to the origin and history of Moon. More amazingly, helium-3 solar particles implanted in solar rocks represent a potential much cleaner and safer source of nuclear energy. Scientists claim that in high energy collisions, these particles would release more energy and less waste than traditional nuclear reactors; since there is no helium-3 on planet Earth, our closest supplier is the lunar soil.
Water
Water, a major source of life on Earth, has long been suspected to exist on the Moon; however, scientists have struggled for many decades to prove that until they finally did. The suspicion was proven true in 2009 when NASA deliberately crashed the two-ton rocket Centaur accompanied with LCROSS (Lunar Crater Observation and Sensing Satellite) into the Cabeus crater near the Moon's south pole, discovering dozens of liters of water ice. Findings of later exploration of lunar water reservoirs reached about 600 million metric tons distributed among polar craters that remain in permanent shadow.
There are different scientific hypotheses regarding the source of lunar water. One theory suggests that hydrogen molecules carried to the Moon by solar wind reacted with compounds containing oxygen in the Moon rocks producing H2O. Another proposes that it resulted from meteors crashing into the Moon's surface, because these bodies contain hydrated minerals and their cores are nearly pure ice. A third theory claims the Moon has a water cycle through which it migrates to the poles from lower latitudes; this hypothesis also suggests that water could have emerged from underground water-rich reservoirs to the surface through volcanic eruptions.
Scientists think of water discovery on the Moon’s surface as a step towards a better understanding of the origin and evolution of the Solar System as a whole, in the same way samples from Earth surface reveal facts about ancient geological events. They believe that if water exists in sufficient quantities, it would turn the Moon into a permanent space station, a lunar base that supports manned explorations of farther celestial body; it could be drunk by astronauts and turned into oxygen to make the Moon habitable. Moreover, the presence of water besides hydrogen gas, ammonia and methane could be exploited to produce fuel.
Air
Extremely tenuous as the lunar atmosphere is, astronauts need not worry about wind should they decide to play golf on the surface of the Moon! According to Anthony Colaprete, NASA Ames Research Center in Moffett Field, California, the lunar atmosphere is so fragile that “it is technically considered an exosphere, not an atmosphere; a cubic centimeter of Earth's atmosphere at sea level contains about 100 billion billion molecules, [while the] same volume of the Moon's exosphere contains only about 100 molecules”.
Due to its fragile nature, lunar atmosphere is hard to study with humans and/or machines working on the Moon’s surface, as they quickly disturb its fragile composition, swamping its natural composition. For example, analyzing data of atmospheric properties measured by Apollo(4) astronauts’ machines was difficult because machine gases had a significant effect on the studied data. Nevertheless, lunar atmosphere remains of high scientific interest; as early as 2013, NASA will be launching the Lunar Atmosphere and Dust Environment Explorer (LADEE), aiming to study it better than ever before. However, what do we already know about the composition of lunar atmosphere?
The main gases composing the lunar atmosphere are neon, hydrogen and helium, in roughly equal amounts. Other gases detected in small amounts include methane, carbon dioxide, ammonia, argon and even water vapor. These gases come from different sources; mainly outgassing—gas emissions released from the Moon’s interior as a result of seismic activities—and capture of particles from solar wind, which originates from the Sun's hot corona(5) and carries gas molecules along to the Moon.
Due to the Moon’s low gravity, lunar atmosphere gases are easily lost to space; light gases escaping faster than gases of heavier molecules. Argon, for example, condenses due to the very low lunar night temperatures; while light gases, such as helium, which originate in the solar wind remain in the atmosphere and escape faster. Solar wind, thus, plays a very significant role in maintaining the lunar atmosphere as it carries constant supplies of gas molecules that makes for the escaping ones.
Fire
It is technically impossible to light a fire on the Moon, for you cannot secure sources of fuel, heat and oxygen needed to sustain a fire flame. Yet, the associations of the fourth element such as light, heat and glow manifest in one way or another on the Moon’s surface.
During daytime, sunlight is brighter and harsher on the Moon than it is on Earth because there is no atmosphere to scatter it and no clouds to shade it. At night, the Moon is lit up by sunlight reflected from Earth, and since Earth is much larger in size, lunar nights are brighter than Earth nights.
Lunar temperatures are also of a very unique nature; it can reach 107°C during the day, dipping down to -153°C during the night. This drastic drop is due to several reasons. First of all, as mentioned earlier, the Moon’s atmosphere is very thin and thus heat easily escapes it. Also, the Moon takes 27 days to rotate once on its axis, which means that a single night on the Moon’s surface is two weeks long.
As bright as a glowing fire, glowing spots on the Moon’s surface were detected, yet, they were not fiery. Scientists observed the appearance of a series of glows on a large lunar crater that kept changing in shape until they finally faded. Such glows are believed to be caused by escaping gases that lift dust above the lunar surface into sunlight. At the same time, a series of fractures developed on the crater floor; they were believed to be the source of the escaping gases.
The four elements of Earth’s nature are all present in different forms on the Moon; yet, they do not support any form of life over there. However, science is an endless race and “unquestionable facts” have no place in a world where new discoveries are made everyday. The Moon’s four elements can qualify it as an expansion of the Earth's economic sphere or a testing place for new technologies. Scientists are already speaking of types of bacteria that can be implanted into lunar soil and can survive such gloomy conditions; who knows what is next?
Glossary
- Igneous rocks are formed by the cooling and solidifying of molten materials.
- Sedimentary rocks are formed through the deposition and solidification of sediments transported by water, ice and wind. Sedimentary rocks are often deposited in layers, and frequently contain fossils.
- Lunar Maria are dark rocky spots on the Moon. The word “maria” means “seas” in Latin; these spots get their name due to their ocean-like appearance in contrast with surrounding lighter spots.
- The Apollo Program is a series of NASA space missions that have been launched to the Moon starting from 1969 until today; the missions land men on the Moon and return them to Earth.
- The Corona is a huge region around the Sun, the temperature of which is so high that the Sun's gravity cannot hold on to it, thus emitting solar wind.
References
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