The Earth's Moon - Summary of Findings Part 4

Last chapter in the series covering the moon, including analysis of findings of water ice inventions on its surface

Earth's Moon Summary of Findings Part 1
Earth's Moon - Summary of Findings Part 2
Earth's Moon - Summary of Findings Part 3

water ice

Clues to the possible presence of water on the moon were found in soil samples brought back by the Apollo pilots. In the basalt block is the mineral apatite (a mineral containing calcium phosphate). What is found is hydrogen in the form of a negatively charged hydroxyl (-1 OH) within the lattice structure of the mineral apatite (1). In the soil samples brought by the Apollo 17 pilots, water was found together with volatile elements in magma, which are themselves trapped inside crystals that are inside beads of volcanic glass (2).

The first attempt to check if there is indeed water on the moon was done using the Clementine spacecraft. It was not a direct observation of bodies of water, but an indirect one. Using the spacecraft's antenna dish, radio signals were broadcast to various areas around the South Pole, places where water ice can be hidden. After that, using radio antennas on Earth, they began to look for reflections of the signals in the antenna plate of the clematis that were transmitted to Earth. It turned out that reflections of water mixed with the earth were indeed returned from the moon. According to the analysis of the findings, they came to the conclusion that the depth of the ice is 15 meters and it covers an area of ​​56 square kilometers. Inside the craters there is ice whose volume is at least 1.6 million cubic meters in the dark areas. It is possible that the origin of this water is from thousands of comets that hit the moon in the last 3 billion years. A comet hitting the moon releases water vapor that surrounds it above the surface of the ground, but some of it descends to the ground in places where the temperature is 40°C above absolute zero and they cannot leave there. For 3 billion years the ice accumulated in a significant amount (3). According to the total calculations carried out, 11-300 million tons of water ice are found in these places (4). Additional evidence for the presence of water was also found by the Lunar Prospector. The evidence of water was found at both poles. According to an estimate, the amount of water ice in the North Pole is 2 times greater than that of the South Pole (5). This evidence was also confirmed by the Indian spacecraft Chandryaan (6).

In an article published in Nature in July 2010, it was reported that in photographs taken by the Indian spacecraft Chandryaan, "lunar dew" was found on the surface. It turned out that water is more common than thought on the surface and inside the moon with some similarity to water inside volcanic systems on Earth. The origin of the "lunar dew" is probably in the solar wind which brought with it hydrogen that came into contact with the lunar oxygen. The water reported in Nature probably comes from a completely different source. They may have been brought by meteorites that hit the moon that probably contained water ice. The existence of volcanoes that were active 4 billion years ago gives researchers a hint that water was once inside the moon. The reason is that the dynamics of volcanoes on Earth and the Moon is primarily driven by water (7). The LRO spacecraft detected forms of frost in the dark regions of the poles (8).

Temperatures

Measuring temperatures on the moon showed extreme differences between day and night and it is not difficult to understand why. During the day the temperature can reach 130 ° C and at night 180 ° C - (9). It should be taken into account that there are places where there will be low temperatures even during the day. It means shadowed places. Every rock and every mountain casts a shadow on their surroundings and like on a globe of light the length of the shadow is conditioned by the position of the sun in the sky. The coldest places in the shadow areas will be in their center (the hypothesis of the writer-Haim Mazar). The first reference to the relationship between temperature and different gases on the surface of the moon arose when they began to think about programming the reality of argon gas at the poles. In these places its concentration will be greater than anywhere else on the moon. From measurements made by the LRO spacecraft it became clear that the poles of the moon are the coldest places in the solar system and for this reason the organization in these places will be in a solid state (10). Without sunlight the temperature range can be C °173.9- C °238 – (K ° 100- K ° 35) (11).

atmosphereה

Surprisingly, the measurements made by the Apollo spacecraft revealed that the moon has an atmosphere, albeit a very thin one. For this reason it is more appropriate to call it Ecosphere. It is created as a result of continuous evaporation of materials on the surface. And they are lost in space or they return to the ground. These processes occur on a daily basis although there is always some atmosphere. The various gases in it are recycled through it. This type of atmosphere is found on comets. Terrestrial observations made in 1998 showed that this atmosphere contains sodium vapor and that the moon has a long tail of sodium gas. It can be observed up to a distance of 800,000 km from the moon. It turned out that when the moon is at birth, the sodium atoms need two days to reach the earth. They are pushed away from the moon by the pressure exerted on them by sunlight. They are drawn to Earth by its gravity and focused into a long, narrow tail (12).

Surprisingly it turned out that despite its thinness, the atmosphere has an ionosphere. The first evidence of this came in the 70s from the Russian spacecraft Luna 20 and Luna 19. The spacecraft's instruments noticed a layer of charged particles rising tens of kilometers above the ground. 20 electrons were found in each cm1000, 1000 times more than they thought. Supporting evidence for this observation was found when radio waves coming from distant sources in space pass near the limb of the Moon. Other factors that contribute to this atmosphere are small amounts of gas resulting from radioactive decay that leak out of the moon's interior. Other sources are meteors and the solar wind spewing atoms from the ground. The dust mentioned in the previous chapter also contribute to the ionosphere (13).

The Chandrayan spacecraft has detected a flux of ions on the night side. It turned out that the moon is a large source of high-energy neutral hydrogen atoms. 20% - 15% of the protons found in the solar wind that hit the lunar surface are returned to space as neutral hydrogen (14). According to the LCROSS and Lunar Prospector findings, the greatest concentration of hydrogen is found at the poles and that in comparison between the poles, the greatest concentration is at the North Pole. It seems that the source of this is the water ice in the shadowed craters at the poles (15).

the crust of the moon

Based on the findings of the Apollo spacecraft, it became clear that the thickness of the crust at least at the landing sites of Apollo 12 and Apollo 14 is 55-70 km and it probably has two layers. (16). The thickness of the crust on the hidden side is 70 km (17). According to the findings of the LRO spacecraft, there are differences between levels (topographically) on the surface of the crust and that the surprising presence of silica was confirmed in 5 different places (18). Some of the impact craters penetrate deep into the crust and can be used to learn about the structure and composition of the moon. A few craters with a diameter of a few kilometers penetrate to a depth of hundreds of meters and larger craters such as the Tycho crater with a diameter of 85 km penetrate to a depth of tens of kilometers (17).

The nucleus

The Lunar Prospector also provided information regarding the core of the Moon. According to one of the models, the diameter of the core ranges from 220-450 km. If the size of the nucleus is the smallest between these values, then it is made of pure iron. If the larger of these values ​​is the correct one, then its density is lower and it is made of iron sulfide. And its mass is between 1%-4% of the moon's mass (19). According to another study, the size of the nucleus is between 500-860 km. In this case its mass is 2% of the moon's mass (20). There is indeed a difference between the results of the two studies, but you can get a pretty good idea about the size of the nucleus.

From testing the soil samples brought back by the Apollo 11 pilots, it became clear that in the distant past the moon had a liquid core that acted like a dynamo for a longer period of time than they thought. What motivated Dynamo is unclear. According to one explanation the lunar dynamo behaved similarly to that of the Earth. As the Earth began to cool, its liquid core began to move and supported the dynamo and the magnetic field that this dynamo created. On earth this dynamo is still active. Regarding the moon, it was hypothesized that this dynamo was powered mainly as a result of the cooling of the moon's interior and that it could have existed several hundreds of millions of years after the formation of the moon (21).

magnetic fields

Examination of the soil samples brought back by the Apollo pilots showed that some of them were magnetized, indicating that they had been exposed to magnetic fields in the past. In addition to this, spacecraft moving in coffee orbits around it noticed areas of magnetic anomalies, places where magnetic fields rise from the rocks. These findings led to the development of an unusual hypothesis. The moon used to have its own strong magnetic field. The strength of this magnetic field was 2 times greater than the Earth's magnetic field. Today, the impression received based on these findings is that the moon used to have a small iron core and that the magnetic field there was created 3.2-3.6 billion years ago, a period when lava flows erupted out onto the ground... in order to develop the magnetic field the core has to be molten. In this situation, convection currents develop, following which heat bursts out to the surface of the ground. The surface of the core cools and returns inward to the moon in the form of a denser column. This circulation of the molten iron acted like a dynamo and created a dipole field like that of the Earth today (22). An article published in July 2012 in Science presents a similar approach based on analysis of samples brought by the Apollo 11 pilots and according to which a molten core with convection currents created a strong magnetic field 3.7 billion years ago, although it is not clear what drove this dynamo. It is possible that this dynamo held its own like the core of the earth. As the moon cooled, its molten core began to move and supported the dynamo and magnetic field it created. According to various models, if the lunar dynamo had sustained itself only by internal cooling of the moon it could have existed only several million years after the formation of the moon (21).

The findings of the Lunar Prospector spacecraft indicate that the core was molten at least 3.6 billion years ago, a time when the impact of asteroids and large meteors on the ground ended. The spacecraft's magnetometer found traces of magnetism trapped in patches of the crust. Those impacts were probably so powerful that the rocks shook with such a strong force that it left a signature of the magnetic field. This means that the strength of this magnetic field at that time is that the dynamo action of metal flow in the crust created a magnetic field as strong as that of the Earth. One of these spots has such a strong magnetic power that it deflects from the surface charged particles from the solar wind, to the same extent as the Earth's magnetic field. This phenomenon was already noticed by the space probe Explorer 35 which circled the moon in 1967. This finding can also indicate that the moon's core in the past was molten iron and had a strong imprint of a magnetic field (19).

The Lunar Prospector mapped the magnetic fields of the lunar crust and also observed the interaction between the solar wind and different areas on their surface with strong magnetic fields at latitudes S °80 - S °30 and at an altitude of 100 km from the ground. Electron reflection maps in the areas on the opposite side (antipode) to the Imbrium Serentatis basins, reaching up to S ° 80 latitude show that magnetic fields in the crust fill most of the antipode areas of these basins. These findings confirm the hypothesis that the impacts that create the basins create magnetic fields in the lunar crust in the antipode regions. The magnetic fields in the Imbrium basin are strong enough to deflect the solar wind and create a tiny magnetosphere, magnetic pockets up to hundreds of kilometers long and a system of shock waves (23). The Indian Chandrayan spacecraft did discover that the moon has its own magnetosphere, albeit a very small one (24).

Polar migration

It appears that at different times during the Moon's history, the magnetic field was in different directions relative to the crust. Calculating the strength and direction of the moon's magnetism led to a number of conclusions that touch the history of the Earth and the Moon as a single system and the Moon itself. It appears that the lunar body has changed its position relative to its axis of rotation around itself. The axis kept its position in space, but the moon revolved around itself so that areas that used to be at the poles are now closer to the equator, this phenomenon is called polar migration. This is because from the point of view of someone on the ground, it seems to him that the poles are the ones that change. Combining this conclusion with the location of several craters led to another conclusion that several large bodies circled the moon and broke up, each of them reaching the ground and leaving their mark in the form of a chain of craters near what was at that time the moon's equator. It seems that these injuries caused the migration of the poles (22).

the wind of the sun

Findings in recent years have revealed a new type of interaction between the solar wind and atmosphereless bodies in the solar system. Areas called magnetic anomalies mainly on the hidden side deflect the solar wind on the hidden side of the moon and thus protect the ground. The accepted assumption was that the solar wind is absorbed by the ground, but findings from the Chinese 1 Chang'e spacecraft, the Japanese Kaguya spacecraft, and the Indian Chandryaan spacecraft showed that this interaction is more complex than they thought. A significant and powerful flux was observed on the lunar surface, probably due to the solar wind reflected from the regolith on the surface.

Mapping the high-energy atoms coming from the moon showed that about a fifth of the photons of the solar wind reaching the moon are returned back to space. A similar phenomenon was observed on Mars' tiny moon Phobos by the Mars Express spacecraft. In a detailed analysis of different regions on the moon it became clear that this diversion of the solar wind is done by an accumulation of magnetic anomalies in the southern hemisphere on the hidden side of the moon (25).

A flux of ions was also discovered on the night side of the moon, which is a large source of neutral and powerful hydrogen atoms. 20% - 15% of protons from the solar wind are returned to space and in a neutral state. A small amount of the hydrogen is absorbed by the soil ((14.

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