The Moon We Step On – Magazine ?

It has been 40 years since a human being first set foot on the Moon. Since then there have been more manned missions; The rocks and data provided by these trips have answered some questions about our satellite, but many questions still remain.

40 years ago a human being set foot for the first time on the surface of another world: the Moon. Between 1959 and 1976 our satellite was visited first by robot probes and then by humans, and then fell into oblivion. More than a decade later, three automated probes visited the Moon. Today, those who dream of returning face an unfavorable outlook: the two powers that dominated space for decades are bankrupt, the space shuttles are obsolete and there is nothing to replace them with, and, for a change, the problem has political aspects. In the midst of this mess it would be worth answering the question, why do we want to return to the Moon?

old moon

It all started when George Bush, former president of the United States… Well, actually it started before, when John F. Kennedy announced… Of course this would not have happened if it were not for World War II…

Perhaps it is best to start at the beginning, when Galileo Galilei discovered the Moon.

You could say that it was Galileo who really discovered the Moon. Before it, our satellite was considered a white, spherical and perfect object that reflected the light of the Sun, turned red on occasions and from time to time eclipsed the sun, but we knew nothing about the nature of the Moon. In 1609 Galileo built a telescope and began to peer into the sky. Observing the Moon he noticed that the border between the day and night hemispheres looked continuous when it crossed the dark regions and irregular when it crossed the bright areas. His conclusion was that the former were plains and the latter were mountainous lands, and he even estimated the height of the lunar mountains. In 1610 Galileo published these and other astronomical discoveries in the book The sidereal messengerwith engravings of his observations of the lunar surface.

Thus the Moon began to lose its magical character and look more like the Earth. A few decades later, Francesco Maria Grimaldi built instruments to examine the geology of the Moon, and together with Giovanni Battista Riccioli he produced the first map of the lunar surface. Grimaldi and Riccioli named many craters on the Moon. Those names are preserved to this day.

It was not until 1837 when Wilhelm Beer and Johann Heinrich Mädler made the first exact map of the Moon and established that our satellite has no water or atmosphere. By then our knowledge of the Solar System encompassed several moons of Saturn and Jupiter, the planets Uranus and Neptune, and some asteroids.

During the 19th century, the Moon was the subject of an interesting debate: the origin of craters. Most geologists thought they were volcanic calderas, like all known terrestrial craters at that time. The English astronomer Richard Proctor proposed that the craters on the Moon were traces of impacts, but very few scientists accepted the hypothesis. American geologist Grove Karl Gilbert showed that calderas have a different structure than impact craters. He further deduced that the relative age of an impact could be calculated simply by observing how the craters overlapped, and that the more impacts there are in a region, the older its soil. This method is still used to determine the age of the surfaces of moons and planets without atmospheres.

Already well into the 20th century, another geologist, Eugene Shoemaker, created astrogeology at the US Geological Survey, an American government institution dedicated to geological studies. Shoemaker began a detailed study of the geological characteristics of our satellite with a view to achieving one of the greatest feats in history: taking a human being to the Moon for the first time.

New Moon

In the period known as the Cold War, the United States and the Soviet Union engaged in a technology generation race to show their power. Conquering Earth was not possible, but outer space was open territory. The Soviets arrived first with the Luna project, a series of devices that orbited our satellite and landed on its surface between 1959 and 1976. Moon 1 It was a failure, but the second attempt, Moon 2reached the surface of the Earth satellite, although it did not survive the impact. Moon 3 He showed us for the first time the hidden side of the Moon (the Moon takes the same time to rotate on its axis as it does to rotate the Earth once, so we always see the same face). He Moon 24last in the series, was released in 1976.

The year 1961 was very active for lunar missions. The United States launched the first satellite of the project Ranger (satellite that failed). By then the Soviet Union had launched several probes and although only one had been successful, the US government decided that the only way to win the space race was to send something more interesting than a robot. On May 25, 1961, President John F. Kennedy announced the project to send humans to the Moon. Eight years and many millions of dollars later, astronaut Neil Armstrong became the first human being to set foot on the Moon.

There were six more manned missions. The rocks and data that these trips provided gave us some answers about our satellite, but they raised many questions, including…

Where did it come from?

By the 1970s, the Moon had been walked on and photographed from its surface, and there were more than 400 kilos of lunar rocks in terrestrial laboratories. However, our cold neighbor kept her secrets from her. Nobody knew how it was formed. There were three hypotheses, which can be summarized as follows: fission, capture and condensation. The first proposed that the Moon somehow became detached from our planet during the initial stages of the formation of the Earth. The scar that remained was the Pacific Ocean. This hypothesis was based on the fact that the lunar composition is similar to that of the Earth’s mantle, the region inside the planet that is between the core and the crust. The problem was that it could not be explained how the landslide occurred. According to the capture hypothesis, the Moon is an independent object that was trapped by the force of Earth’s gravity. But this hypothesis could not explain the properties of the satellite’s orbit: its distance from the Earth and its translation speed. The condensation hypothesis assumes that our planet and its satellite formed together, but in that case they would be very similar in composition, which is false.

As if that were not enough, one more hypothesis was suggested: that of the great impact. According to this, the Earth was hit during its formation by an object the size of Mars (about half the size of our planet). The impact released a large amount of material that began to rotate around the Earth and then condensed. The proposal did not please most scientists and for a decade it was not given importance, until in 1984 a meeting dedicated to the origin of the Moon was organized. The specialists analyzed in detail all the hypotheses, as well as the observations that supported them. The consensus leaned in favor of the impact hypothesis.

The origin of our satellite, however, is not yet a closed case. The hypothesis has to explain all the characteristics of the Moon and not just a few. The most recent work involves computer modeling to determine exactly what type of impact would give rise to the observed properties.

The hidden side

It is also called “the dark side of the Moon”, but it is not such a thing. When the side we see is dark (new moon), the hidden side is illuminated. In addition to the fact that we cannot see it from the earth’s surface, the hidden side has other curiosities. The most notable is that it lacks the dark areas of the visible side, which we call “seas”. Today we know that these regions are plains of volcanic material.

Thus, the scarcity of seas on the hidden side indicates that volcanic activity was less in that hemisphere. For many years this inequality was a mystery. Volcanism is due to the heat from the interior of a planet or satellite, and that heat would have to be transferred homogeneously from the interior to the surface. If that did not happen, it meant that the interior of our satellite is not homogeneous, that is, the concentric layers of its interior do not have the same composition, density and thickness throughout its entire length.

But we were not able to corroborate it until 1994, when the American probe Clementine orbited the Moon. The probe generated the first digital database of lunar geography and, among other things, measured the surface variations of the satellite’s gravitational field. The force of gravity increases with the mass of objects and decreases with the distance between them. In the case of planets, the gravity field has small variations that reveal deviations in the thickness and density of the subsurface. Are radiation anomalies They allow us to determine properties of the interior of a planetary body without having to dig.

With measurements of gravitational anomalies made by the Clementine probe, it was determined that the far side of the Moon has a thicker crust on average than the other hemisphere. The differences can be very large: at the bottom of some craters the crust is only four kilometers thick, while there are regions where the thickness reaches 100 kilometers. Another probe revealed in 1998 that there are greater amounts of radioactive elements in certain areas. The atoms of radioactive elements release heat when they decay (and are one of the sources of the Earth’s interior heat). This inhomogeneity on the Moon could have contributed to more volcanic activity on one side than the other. Of course, this is the what and not the why of the difference between the hidden and visible hemispheres. The causes of the difference can be divided into two: external ones, for example, impacts, and internal ones, such as the formation processes of the core or the movement of material in the area known as the mantle. This is a question that scientists have not yet resolved.

Water on the Moon?

The probe Clementine found ice on the Moon, but there was so much information that the spacecraft sent that scientists did not realize it until they reviewed some of the data in more detail. He…