Understanding the Interior and Atmosphere of the Moon

President John F. Kennedy echoed the call "We choose to go to the moon in this decade and do the other things. Not because they are easy, but because they are hard…” in his legendary speech at Rice University, Houston, Texas (USA) exactly half a century ago, soon the newly established US space agency (NASA) was busy. In addition to having to prepare a heavy rocket capable of driving a special spacecraft to land on the Moon and bring back passengers to Earth safely, they also must think about what to do on the Moon. Although it has been known since the beginning of human civilization, up to half a century ago the Moon is virgin territory, a region completely unknown to its characteristics. The Status of the Moon at the time was the same as the Antarctic region before the 20th century. Though heavier on the political side, the landing mission of humans on the Moon is also burdened with the scientific side to recognize the Moon in geological, meteorological and geophysical perspectives that manifest in the effort of mapping the surface (topography) to a certain resolution, understanding the interior (interior) of the Moon, understanding the dynamics of distance Earth-Moon, recognizing the characteristics of gas emissions from the surface of the Moon, recognizes the interactions of the Moon with solar wind radiation and Earth's magnetosphere as well as other related aspects.

With that purpose, the lunar human landing mission that manifests itself as an Apollo program is not a stand-alone space mission, but a counterpart of unmanned space missions such as the Surveyor program. That way the Apollo program not only transports cameras but also brings with it a variety of scientific instruments that will produce a variety of non-photographic data. Some of these instruments are placed permanently on the Moon with the resulting data transmitted regularly to Earth for analysis. These non-photographic data do present a much different impression than the photographs of each Apollo mission, as they are generally only a series of curves, graphics, and maps with lower resolution. However, these data can present important information that is often not captured by the camera or the human eye, which allows us to comprehend the Moon comprehensively. In our daily lives, the position of photographic and non-photographic data can be paralleled by a photograph with specific data such as dental records, fingerprints, iris (eye), medical or genetic record (DNA) that can present a high-precision personal identification in the realm of law.

The Apollo program manifested itself in six human landing missions on the Moon from July 1969 to December 1972, ie in Apollo 11 to 17 missions except Apollo 13 which failed to land because of very serious technical problems. Each mission landing 2 astronauts, so as a whole there are 12 humans who ever set foot on the Moon. They are in charge of collecting a number of rock samples and Moon soil, carrying out various experiments and installing a permanent scientific instrument.

Interior of the Moon

Our knowledge of the interior of the Moon is contributed by a number of instruments such as the seismometer, magnetometer, retroreflector mirror, and Moon surface heat flow meter as well as various special experiments such as Lunar soil mechanical experiments, active seismic (reflection seismic) and electrical conductivity test of Moon rocks.

A seismometer is a seismic wave recorder (seismic), while the magnetometer is in charge of recording magnetic fields. The retroreflectors mirror is a special mirror designed to reflect back a beam of light that hits it to its light source position. And the surface heat flow meter of the Moon is an instrument equipped with a number of thermometers to measure the temperature gradient of the Moon's soil layers. Lunar ground mechanical experiments were performed using a hand drill to test the hardness, the size of the Moon's crystal and its physical properties. While the active seismic experiment is carried out by detonating a number of dynamite/explosives at certain points so as to produce artificial seismic waves propagating through the layers of Moon rock to be received by a series of geophones. And the electrical conductivity test is carried out with a transmitter placed on the receiver. The position of the transmitter and receiver is then shifted periodically using the Moon car (Lunar Rover). Except for the retroreflector mirror, the placement and operation of all those instruments and the execution of all experiments is not done without direct human intervention.

The Moon's interior is generally divided into three layers: crust, sheath (mantle) and Moon core. The Moon's crust is quite thick, with a thickness of 60 to 70 km or an average of 3 times thicker than the Earth's crust. The Moon's crust is dominated by alkaline basaltic igneous rocks, where up to a certain depth (1.4 km at the Apollo 17 landing site) undergoes intense cracking and/or bracketing due to repeated comet/asteroid hits throughout the Moon's geological history. The same blow also makes the surface of the Moon covered with very fine dust (regolith) (diameter <0.1 mm), very dry and charged with static electricity so that it can adhere strongly to the astronauts or other equipment. Up to a depth of 2 km of Moon rock is very dry and contains no water.

Unlike the Earth, the Moon's crust does not have a tectonic plate system. This is caused by the solidification of the moon layer (mantle) of the Moon so as not to allow the circulation of convection currents. Because it is a very rare occurrence of a hypocentral of shallow and medium moon earthquake. Almost all the earthquakes of the moon are sourced at a depth of 800 to 1,000 km. Electromagnetic sounding experiments using magnetometers ensure the Moon's interior is liquid at a depth of 800 to 1,500 km. This fact ensures the moon earthquakes are generated by the liquid dynamics of the Moon interior located in the transition zone of the sheath and Moon core. The dynamics are influenced by the Earth's tidal style. With the liquid part lying very deep from the surface, the Moon is geologically dead. There is no trace of volcanism and/or tectonic activity in the moon's crust today. This is supported by the small value of the surface heat flow of the Moon, which is only (average) 21 milliwatts per square meter (18-24% of Earth surface heat flow). Seismic data also do not indicate the presence of dotted hypocentral points at various depths, commonly found in the magma channels on Earth. With dead volcanism and tectonism, the annual seismic energy released by the Moon is only 1/10 million of Earth's annual seismic energy.

Below the sheath layer is a Moon core of 350 km in diameter. The rotation pattern is the same as the whole rotation pattern of the Moon section. Supported by the slow rotation period of the Moon, the Moon cannot form an intrinsic magnetic field like the Earth, so there are no magnetic poles on the Moon at this time. But in the past, the Moon once had a magnetic field, especially in the youth of the solar system. The remnants of the magnetic field This moon is still scattered in various localized points with very weak strength.

Atmosphere of the Moon

We know the Moon as a vacuum, but it is not entirely so. The Apollo mission also landed several instruments to analyze the spaces on the Moon's surface, such as cold cathode tube instruments and solar wind gauges.

The moon turned out to have an atmosphere, though very very thin so that the air pressure was very low. Each square meter of the Moon's surface contains 2 billion air molecules with a density of only 1/100 trillion Earth's atmosphere. The total mass of the Moon's atmosphere is only 10 tons so that every time a human landing mission on the Moon causes a very significant disruption. So that the investigation of the atmosphere can only be effective many days after humans leave the surface of the Moon. Moon's atmosphere only exists at night. During the day, the dominance of high-speed solar wind particles causes Moon's moon molecules to kick into space.

The solar wind is the energetic particles that the Sun exhales continuously throughout the whole, with 95% of the form of protons and electrons. The remainder is positive ions of the isotopes Helium-3, Helium-4, Neon-20, Neon-21, Neon-22, and Argon-36. The number of solar protons received by the Moon depends very much on the Moon's position on Earth and the Earth's magnetosphere. From the 27th day of the Moon's revolutionary period, 18 days of which placed the Moon outside the Earth's magnetosphere. At that time the Sun proton received by the Moon's surface in each cubic meter of the Moon reaches 100 thousand to 200 thousand grains that skyrocketed at speeds varying from 450 to 650 m / sec. While within 5 days then the Moon passes in the Earth's magnetosphere so that none of the Sun's protons are detected. And in the remaining 4 days, the Moon passes across the boundary of Earth's magnetosphere so that the Sun's protons are able to reach the Moon's surface but at a much lower speed.

The knowledge of the interior and atmosphere of the Moon is a fragment of the heritage of the landing program on the Moon. such abundant non-photographic data makes us multiply more understanding of the Moon after the Apollo program than the previous era, even since the era of human civilization began. With such abundant data and so far none of the relevant scientists who question its validity in terms of its specific characteristics, it is rather ridiculous to witness a group of people who try to deny the occurrence of a human landing on the Moon and consider it a mere conspiracy, let alone only supported unilateral photographic interpretation. On the other hand, the placement of geophysical instruments scribbles the borderline that separates human success stories in terms of exploration of the Moon and Mars. On Mars, though explorations have been going on since the 1970s to the present and the latter marked the landing of Curiosity's cruise robot (Mars Science Laboratory mission), but the absence of a human landing causes our achievement on Mars not as good as the Moon. For example, until this moment we have never managed to drill the land of Mars to as deep as more than 0.5 m. Until this moment we have not succeeded in placing a seismometer to detect mars earthquakes or measure the flow of surface heat to ensure its tectonic and volcanic status. And like what exactly the interior of Mars was until now we can not be sure, except only guessing through satellite data. Even to ascertain whether the land of Mars really contains water or not, until now we only deduce it indirectly.

Reference :

1. https://www.space.com/19582-moon-composition.html
2. https://www.space.com/18067-moon-atmosphere.html
3. https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html
4. https://www.windows2universe.org/earth/moon/lunar_interior_structure.html

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