Moon

The Moon is the only natural satellite of planet Earth . Its diameter is about 3476 km, about a quarter of the Earth. The mass of the Moon is 81 times less than that of the Earth. The Moon’s average density is only three-fifths that of Earth, and its surface gravity is one-sixth that of Earth.

Summary

[ disguise ]

• 1 Origin
• 2 Lunar relief
• 3 Lunar observation
• 4 Higher resolution image
• 5 Training
• 6 Revolutions of the Moon
  • 1 Lunar translation movement
  • 2 Rotational movement
• 7 Orbit of the Moon
• 8 Tides
• 9 Atmosphere of the Moon
• 10 Lunar Exploration
  • 1 Other missions
  • 2 False color mosaic of the Moon
  • 3 Lunar South Pole
  • 4 Apollo 11
  • 5 Apollo 17: the discovery of orange soil
  • 6 Copernicus Impact Crater Terminator
• 11 Possibility of living there
• 12 See also
• 13 Sources

Origin

Upon discovering that the composition of the Moon was the same as that of the Earth’s surface, it was assumed that its origin had to come from the Earth itself . A body so large in relation to our planet could hardly have been captured nor was it likely to have formed next to the Earth.

Thus, the best explanation for the formation of the Moon is that it originated from the pieces left after a cataclysmic collision with a protoplanet the size of Mars at the dawn of the solar system (great impact hypothesis). This hypothesis also explains the large axial inclination of the Earth’s axis of rotation, which would have been caused by the impact.

The enormous energy supplied by the collision completely melted the Earth’s crust and threw a large amount of incandescent debris into space. Over time, a ring of rock formed around our planet until, through accretion , the Moon was formed. Its initial orbit was much closer than its current one and the Earth’s day was much shorter as the Earth rotated faster.

For hundreds of millions of years, the Moon has been slowly moving away from the Earth , while the speed of Earth’s rotation has decreased due to the transfer of angular momentum that occurs between the two stars. This retreat process currently continues at a rate of 38 mm per year.

After its formation, the Moon experienced a cataclysmic period, dated around 3,800-4,000 million years ago, in which the Moon and the other bodies of the inner solar system suffered violent impacts from large asteroids. This period, known as late intense bombardment , formed most of the craters observed on the Moon, as well as Mercury .

Analysis of the surface of the Moon provides important data about this final period in the formation of the solar system . Subsequently, there was a period of volcanism consisting of the emission of large quantities of lava , which filled the largest impact basins, forming the lunar seas, and which ended 3,000 million years ago. Since then, little else has happened on the lunar surface other than the formation of new craters due to asteroid impacts .

Recently, however, data sent by the Japanese Selene probe have shown that this volcanism has lasted longer than previously thought, having ended on the far side 2.5 billion years ago.

lunar relief

In 1610 , when Galileo Galilei pointed his telescope at the Moon, he was able to distinguish two distinct surface regions. He called the dark regions “seas,” which are now known to have no water and bear names such as Sea of ​​Serenity and Sea of ​​Fecundity ; They are plains with few craters .

The rest of the lunar surface is brighter, and represents higher regions with a high density of craters , such as Tycho and Clavius . On the lunar surface there are also mountain chains that bear names such as Alps and Apennines , just like on Earth .

The Moon was heavily bombarded in its early history, causing many of the original rocks of the ancient crust to become mixed, melted, buried, or disappear.

The meteoric impacts brought a wide variety of “exotic” rocks to the Moon, so that samples obtained in only 9 of the areas produced many different types of rocks for study.

The impacts also brought to light lunar rocks located at great depths and distributed their fragments over large areas far from their origin, making them more accessible.

The underlying crust was also thinned and fragmented, allowing molten basalt from within to reach the surface. Since the Moon has neither an atmosphere nor water , soil components do not deteriorate chemically as they would on Earth .

Rocks more than 4 billion years old still exist there, allowing for information about the early history of the solar system that is not available on Planet Earth . Geological activity on the Moon consists of occasional large impacts and the continuous formation of regoliths. However, it is considered to be geologically dead.

With such an active early history of bombardment and a relatively abrupt end to large impacts, the Moon is considered fossilized in time .

The dark seas, with relatively few craters, cover about 16% of the lunar surface and are concentrated on the near side of the Moon, mainly within impact basins. This concentration could be due to the fact that the center of mass is displaced from its geometric center by about 2 kilometers (1.2 miles) in the direction of Earth, probably because the crust is thicker on the dark side.

It is possible, therefore, that basalt magmas from the interior easily reached the surface on the near side, but encountered difficulties on the far side.

The rocks of the seas are basalts and most have an age ranging from 3,100 to 3,800 million years.

Some fragments in plateau breccias have an age of 4.3 billion years and high-resolution photographs suggest that some flows in the seas surround young craters and could therefore be as old as 1 billion years.

The seas have an average thickness of a few hundred meters but are so massive that they frequently deform the underlying crust, producing fault-like depressions and uplifted mountain ranges. The relatively bright, crater- covered plateaus are called terraces.

The craters and basins of the plateaus are formed by meteorite impacts and are therefore older than the seas, having accumulated more craters .

The dominant rock type in this region contains high levels of plagioclassic feldspar (a mineral rich in calcium and aluminum ) and is a mixture of fragments brecciated by meteorite impacts.

Most terrace breccia are composed of even older breccia fragments. Other samples from the terraces are fine-grained crystalline rocks formed by impact melting due to the high pressures generated in the impacts.

Almost all of the terrace breccias and impact melt formed 3.8 to 4 billion years ago. The intense bombardment began 4.6 billion years ago, which is the estimated age of the Moon’s origin.

lunar observation

The moon has fascinated humanity throughout time. By simple observation with the naked eye, one can distinguish two broad types of terrain: the relatively bright plateaus and the darker plains.

In the mid- 17th century , Galileo Galilei and other early astronomers made telescopic observations, noting a nearly infinite overlap of craters. It has also been known for more than a century that the Moon is less dense than the Earth.

Although many things have been discovered about the Moon before the space age, this new era has revealed many secrets that were hardly imaginable before this time.

Current knowledge of the Moon is greater than that of the rest of the objects in the solar system except the Earth. This leads to a greater understanding of geological processes and a better appreciation of the complexity of the terrestrial planets.

In many prehistoric and ancient cultures, the Moon was a deity or other supernatural phenomenon. One of the first times that an attempt was made to offer a rational and scientific vision of what the moon was was in Ancient Greece .

It was proposed by the philosopher Anaxagoras who reasoned that both the Sun and the Moon were two giant, rocky, spherical bodies and that the light emitted by the Moon was nothing more than reflected light from the Sun.

In the Middle Ages , before the invention of the telescope , more and more people recognized that the Moon was a sphere since it was believed that it had to be “perfectly smooth.”

In 1609 , Galileo Galilei observed the Moon with a telescope for the first time and stated in his book Sidereus Nuncius that it was not smooth since it had craters. Later, even in the 17th century , Giovanni Battista Riccioli and Francesco Maria Grimaldi drew a map of the Moon and gave names to many of these craters, names that remain today.

Higher resolution image

The highest resolution achieved in September 2021

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In 2021, a new telescope system at the Green Bank Observatory in West Virginia (USA) managed to capture the highest resolution image of the Moon ever taken from Earth using radar technology. The feat took years of work, and the result is spectacularly detailed. The focal point is Tycho crater , one of the most prominent elevations on the Moon.

Training

Several mechanisms have been proposed to explain the formation of the Moon 4,527 (±10) million years ago. This age is calculated based on isotope dating of lunar rocks, between 30 and 50 million years after the origin of the solar system.

These include the fission of the Moon from the Earth’s crust through centrifugal forces, which should have also required an initial spin of the Earth; the gravitational attraction of the Moon in a state of formation, which would have required an unfeasible extension of the atmosphere to dissipate the energy of the Moon, which was passing by.

The co-formation of the Moon and the Earth together in the primordial accretion disk, which does not explain the depletion of Iron in the metallic state. These hypotheses also cannot explain the strong angular momentum in the Earth-Moon system.

The general hypothesis today is that the Earth-Moon system formed as a result of a large impact: a celestial body the size of Mars collided with the young Earth, flying material into orbit around it, which merged to form the Moon. .

It is believed that gigantic impacts were common in the early solar system. Modeling of a large impact through computer simulations agrees with measurements of the angular momentum of the Earth-Moon system, and the small size of the lunar core; They in turn show that most of the Moon comes from the impact, not from the young Earth .

However, Meteorites demonstrate that the isotopic compositions of Oxygen and Tungsten of other bodies in the inner solar system such as Mars and Vesta are very different from those of Planet Earth, while the Earth and the Moon have practically identical isotopic compositions.

Post-impact mixing of evaporated material between the Earth and the Moon may have equalized the compositions, although this is debated.

The significant amount of energy released in the large impact and the subsequent melting of material in Earth’s orbit may have melted the Earth’s surface layer, forming a magma ocean.

The newly formed Moon may also have had its own lunar magma ocean; Estimates of its depth vary between 500 km and the entire radius of the Moon.

Revolutions of the Moon

The Moon takes 27 d 7 h 43 min to orbit the Earth if the rotation is considered with respect to the stellar background ( Sidereal revolution ), but 29d, 12h, 44min if it is considered with respect to the Sun (synodic revolution) and this It is because in this period the Earth has revolved around the Sun. (See month). This last revolution governs the phases of the Moon, eclipses and lunisolar tides.

Since the Moon takes the same time to rotate around itself as it does around the Earth, it always has the same face. This is because the Earth, through an effect called gravitational gradient, has completely slowed down the Moon.

Most regular satellites present this phenomenon with respect to their planets. Thus, until the time of space research ( Luna 3 ) it was not possible to see the hidden lunar side, which presents a dissymmetry with respect to the visible side.

The Sun always illuminates half of the Moon (except in lunar eclipses ), which does not have to coincide with the visible side, producing the phases of the Moon.

The apparent immobilization of the Moon with respect to the Earth has occurred because the Earth’s gravity acts on the irregularities of the lunar globe so that over time the visible part has a 4 km greater radius than the non-visible part, with the center of lunar gravity displaced from the lunar center 1.8 km towards Earth.

• Synodic revolution:it is the time interval necessary for the Moon to return to an analogous position with respect to the Sun and the Earth. Its duration is 29 d 12 h 44 min 2.78 s. It is also called lunation or lunar month.
• Sidereal revolution:it is the time interval it takes for the Moon to return to an analogous position with respect to the stars . Its duration is 27 d 7 h 43 min 11.5 s.
• Tropic revolution:it is the period necessary for the Moon to once again have the same celestial longitude . Its duration is 27 d 7 h 43 min 4.7 s.
• Draconitic revolution:it is the time it takes for the Moon to pass through the ascending node twice consecutively. Its duration is 27 d, 5 h 5 min 36 s.
• Anomalistic revolution:it is the time interval that elapses between two consecutive passages of the Moon through perigee. Its duration is 27 d 13 h 18 min 33 s.

Lunar translation movement

The fact that the Moon rises about an hour later each day is explained by knowing the Moon’s orbit around the Earth. The Moon completes one revolution around the Earth in approximately 28 days. If the Earth did not rotate on its own axis, it would be very easy to detect the movement of the Moon in its orbit.

This movement causes the Moon to advance about 12° in the sky each day. If the Earth did not rotate, what would be seen would be the Moon crossing the celestial vault from west to east for two weeks, and then it would be absent for two weeks (during which the Moon would be visible on the opposite side of the Globe).

However, the Earth completes one rotation every day (the direction of rotation is also eastward). So, each day it takes the Earth about 50 more minutes to be face to face with the Moon again (which means you can see the Moon in the sky). The rotation of the Earth and the orbital movement of the Moon combine, in such a way that the moonrise is delayed on the order of 50 minutes each day.

Taking into account that the Moon takes approximately 28 days to complete its orbit around the Earth , and it takes 24 hours to complete one revolution around its axis, it is simple to calculate the daily “delay” of the Moon:

While in 24 hours the Earth will have made a complete revolution, the Moon will only have traveled 1/28 of its orbit around the Earth , which expressed in degrees of arc gives:

• If we now calculate the time that the Earth takes to travel this arc in its rotation, it gives the approximately 51 minutes that the Moon delays its rise each day.

To notice the movement of the Moon in its orbit, we must take into account its location at the time of sunset for a few days. Its orbital motion will take it to a point further east in the twilight sky each day.

Rotatory motion

The Moon rotates on an axis of rotation that has an inclination of 88.3° with respect to the plane of the elliptical translation around the Earth . Since the duration of the two movements is the same, the Moon constantly presents the same hemisphere to the Earth .

Moon Orbit

The Moon orbits the Earth at an average distance of 384,403 km and at an average speed of 3,700 km/h. It completes its orbit around the Earth , following an elliptical orbit, in 27 days, 7 hours, 43 minutes and 11.5 seconds.

This synchronous rotation is caused by the Moon’s asymmetric mass distribution, which has allowed Earth’s gravity to maintain a lunar hemisphere permanently rotated toward Earth . Optical releases have been observed by telescope since the mid- 17th century .

Very small but real releases (approximate maximum of 0.04°) are caused by the effect of solar gravity and the eccentricity of the Earth’s orbit, disturbing the moon’s orbit and allowing the cyclic preponderance of the torque in the north – south and east directions – west .

To change from one phase to another similar one, or lunar month, the Moon needs 29 days, 12 hours, 44 minutes and 2.8 seconds. Since it takes the same time to rotate around its axis as it does to rotate around the Earth , it always shows us the same face. Although it appears bright, it only reflects 7% of the light it receives from the Sun into space .

Likewise, the Moon moves away about four centimeters a year from the Earth while slowing down the Earth’s rotation, which will cause total solar eclipses to stop occurring in the distant future as the Moon is not large enough to cover the solar disk.

In theory, this separation should last until the Moon takes 47 days to complete an orbit around our Planet , at which time our planet would take 47 days to complete a rotation around its axis, similar to what happens in the Pluto – Charon system .

However, the future evolution of our Sun may disrupt this evolution. It is possible that as our star becomes a red giant in several billion years, the proximity of its surface to the Earth-Moon system will cause the lunar orbit to close until the Moon is around 18,000 kilometers away. the Earth – the Roche limit -, at which point the Earth’s gravity will destroy the Moon, turning it into rings similar to those of Saturn .

In any case, the end of the Earth-Moon system is uncertain and depends on the mass that the Sun loses in these final stages of its evolution.

Tides

In reality, the Moon does not revolve around the Earth , but rather the Earth and the Moon revolve around the center of mass of both. However, since the Earth is a large body, the gravity that the Moon exerts on it is different at each point.

At the closest point it is much larger than at the center of mass of the Earth , and larger at this point than at the furthest point from the Moon.

Thus, while the Earth rotates around the center of gravity of the Earth-Moon system, a force appears at the same time that tries to deform it, giving it the appearance of an egg.

This phenomenon is called gravitational gradient, which produces Tides . Since the Earth is solid, the deformation affects the waters more and is what gives the effect that they rise and fall twice a day (they rise at the points closest and furthest from the Moon).

An associated effect is that the tides slow the Earth in its rotation (it loses energy due to the friction of the oceans with the sea floor), and since the Earth-Moon system has to conserve angular momentum, the Moon compensates for it currently moving away 38 mm each year, as demonstrated by laser distance measurements, made possible by the retro-reflectors that the astronauts left on the Moon.

Moon Atmosphere

The Moon has a negligible Atmosphere due to its low Gravity , unable to retain Gas Molecules on its surface. Its entire composition is still unknown.

The Apollo program identified helium and argon atoms , and later in 1988 , Earth-based observations added sodium and potassium ions . Most of the gases on its surface come from its interior.

The thermal agitation of the gas molecules is induced by solar radiation and by random collisions between the atmospheric particles themselves. In the Earth’s atmosphere , molecules usually have speeds of hundreds of meters per second, but exceptionally some manage to reach speeds of 2,000 to 3,000 m/s.

Since the escape velocity is approximately 11,200 m/s, they never manage to escape into space. On the Moon, on the contrary, since gravity is six times less than on our planet , the escape velocity is also lower, on the order of 2,400 m/s.

We can deduce then that if the Moon once had an atmosphere , the fastest molecules were able to escape from it to, according to a law of the kinetic theory of gases, induce the remaining ones to increase their speed , thus accelerating the process of atmospheric loss.

It is estimated that the complete disappearance of the hypothetical lunar atmosphere must have taken place over several hundred million years.

The virtual absence of atmosphere on our satellite forces astronauts to have autonomous gas supply equipment (known as PLSS) during their walks on the surface.

Likewise, since there is no protective mantle, ultraviolet radiation and gamma rays emitted by the Sun bombard the lunar surface, making it necessary to have special protective suits to avoid their harmful effects.

For the tenuous lunar atmosphere any small change can be important. The mere presence of the astronauts locally alters its pressure and composition by enriching it with the gases they expire and those that escape from the lunar module each time an EVA (extravehicular ride) is carried out.

There is fear that the gases emitted by the ships that landed on the Moon in the 1970s have created pollution or contamination of equal mass to that of their native atmosphere .

Although these gases must have mostly disappeared by now, there is still a concern that remnants will remain that will prevent research into the Moon’s real atmosphere.

The lunar atmosphere also receives contributions from solar particles during the day, which cease when night comes. During the lunar night, the pressure can drop to no more than 2 billionths of the Earth’s atmosphere, rising during the day to 8 billionths, thus demonstrating that the lunar atmosphere is not a permanent atmosphere, but a concentration of particles. dependent on the exolunar environment.

The ionosphere that surrounds our satellite differs from the Earth’s in the low number of ionized particles, as well as the presence of low-energy electrons that, torn from the Moon’s soil, are emitted into space by the impact of the sun’s rays. .

Currently, it has been possible to determine the existence of a sodium tail composed of vapors that are released from our satellite in a similar way to the gases from comets .

The absence of air, and consequently winds, prevents the surface from eroding and transporting soil and sand, smoothing and covering its irregularities.

Due to the absence of air, sound is not transmitted. The lack of atmosphere also means that the Moon’s surface has no protection from sporadic bombardment by comets and asteroids.

Furthermore, once their impacts occur, the resulting craters practically do not degrade over time due to the lack of erosion.

lunar exploration

The Moon is the only celestial body on which man has made a manned lunar landing. Although the Soviet Union ‘s Luna program was the first to reach the Moon with an unmanned spacecraft, the United States’ Apollo program achieved the only manned missions to date, beginning with the first unmanned lunar orbit by Apollo 8 ( in 1968), and six manned moon landings between 1969 and 1972, the first being Apollo 11 (in 1969).

These missions returned more than 380 kg of lunar rock, which has been used to develop a detailed geological understanding of the origins of the Moon (it is believed to have formed 4.5 billion years ago in a large impact), the formation of its internal structure and its subsequent history. (See the article Geology of the Moon ).

Since the Apollo 17 mission (in 1972), it has been visited only by unmanned space probes, notably the Soviet Lunokhod astromobiles .

Since 2004 , Japan , China , India , the United States , and the European Space Agency have sent orbiters. These spacecraft have confirmed the discovery of frozen water fixed to the lunar regolith in permanently shadowed craters located at the poles.

Future manned missions to the Moon have been planned, but not yet launched; The Moon remains, under the outer space treaty, free for exploration by any nation for peaceful purposes.

Other missions

The American spacecraft Clementine and Lunar Prospector , the Japanese Hiten and Selene , the European Smart 1 , the Chinese Chang’e 1 and the Indian Chandrayaan-1 represented a return to the Moon, abandoned since 1973 .

Its mission was to detect the presence of water vapor mixed with lunar dust and coming from comets that have crashed near the lunar poles in craters where they are never illuminated by the Sun.

In September 2005 , NASA announced the project for a new manned trip to our satellite, scheduled for 2018.

In September 2009, it was announced that the Indian probe Chandrayaan-1 , orbiting the Moon, detected thin films of water on the surface.

False color mosaic of the Moon

False color photograph of the Moon taken by the Galileo spacecraft on December 8 , 1992 .

On December 8 , 1992, the Galileo spacecraft took a false color photograph of the Moon. The false color processing used to create this image is useful for interpreting the surface soil composition.

Areas that appear red generally correspond to lunar plateaus, while areas that vary from blue to orange indicate the presence of an ancient volcanic lava flow from a lunar sea or ocean.

Bluer sea areas contain more titanium than orange regions. The Tranquillitatis Sea, seen as a dark blue patch on the right, is richer in titanium than the Serenitatis Sea, a considerably smaller circular area located further up to the left of the Tranquillitatis Sea.

The blue and orange areas covering most of the Moon’s left side in this view represent many separate lava rivers in the Procellarum Ocean.

The small purple areas found near the center are pyroclastic deposits formed by explosive volcanic eruptions. The recent crater Tucho, with a diameter of 85 kilometers (53 miles), stands out at the bottom of the photo.

lunar south pole

This mosaic is made up of 1,500 images of the south polar region of the Moon obtained by Clementine. The top half of the mosaic faces the Earth .

Clementine has revealed what appears to be a large depression near the lunar south pole (center), evident due to the presence of extensive shadows around the pole.

This depression is probably an ancient basin that was formed by the impact of an asteroid or comet. A significant portion of the dark zone near the pole could be in permanent shadow, and cold enough to trap cometary water as ice. The Schrodinger impact basin (at 4 o’clock) is formed by two rings, about 320 kilometers in diameter (200 miles) that have been recognized as the second youngest impact basin on the Moon.

The center of Schrodinger is filled with lava . The volcanic hole seen in the ground of Schrodinger is one of the largest explosive volcanoes on the Moon.

Apollo 11

Apollo 11 .

The Apollo 11 Lunar Module (ML) in the ascent stage, with astronauts Neil A. Armstrong and Edwin E. Aldrin Jr. on board, has been photographed from the Command and Service Module (MSM) during its rendezvous at the lunar orbit.

The ML was carrying out the approach maneuver for docking with the MSM. Astronaut Michael Collins remained on the MSM in lunar orbit while the other two crew members explored the lunar surface.

The large dark-colored area seen in the background is the Smyth Sea, centered at 85 degrees east longitude and 2 degrees south latitude on the nearside lunar surface. This view looks west. The Earth rises above the lunar horizon.

Apollo 17: the discovery of orange soil

Orange soil particles from the Moon.

These orange glass spheres and fragments are the finest particles brought back from the Moon. The particles vary between 20 and 45 microns. The orange soil was brought from the Taurus-Littrow lunar landing site by members of the Apollo 17 crew.

Astronaut scientist Harrison J. Schmitt discovered the orange soil in Shorty Crater. The orange particles, which are interspersed with black, mottled grains, are the same size as the particles that make up Earth’s sediments .

A chemical analysis of the orange soil has shown that this sample is similar to others returned by Apollo 11 from a point (Sea of ​​Tranquility) located several hundred miles to the southwest.

As in those samples, it is rich in titanium (8%) and iron oxide (22%). But unlike the Apollo 11 samples, the orange soil is inexplicably rich in zinc . The orange soil has a probable volcanic origin and is not the result of a meteorite impact.

Copernicus Impact Crater Terminator

Copernicus impact crater

This image of Copernicus was taken by the Lunar Orbiter 5 mission. Copernicus is 93 kilometers wide and is located within the Mare Imbrium basin, north of the near side of the Moon (10° N, 20° W).

The image shows the crater floor , mounds, rim and radial ejecta. The rays of the ejecta are superimposed around the entire crater on the surrounding terrain in a group of the same age that is called the Copernican system, identified as the youngest rock group on the Moon.

Possibility of living there

The Moon’s atmosphere is extremely thin. Composed of hydrogen , neon and argon . There is also plenty of oxygen on the Moon but the Moon’s atmosphere does not have enough oxygen to support human life.

The top layer of rocky soil, known as “regolith” – a layer of rock and dust from which the surface of the Moon is made – does contain enough oxygen for 8 billion people to survive for about 100,000 years or twice as long. Oxygen can be found in many of the minerals in the soil around us. On the Moon, it makes up about 45% of the land.

Can we do anything to extract this oxygen from the regolith? A new joint program between the Australian Space Agency and NASA has committed to sending an Australian rover to the Moon through NASA’s Artemis program to collect lunar rocks as an “attempt to extract oxygen from lunar regolith.” The results have the potential to change civilization as we know it, because if lunar colonists can synthesize breathable air in situ, a long-term lunar base would be much more feasible.

To access oxygen on the Moon’s surface, a lot of energy would be needed. Reactors would be needed to create oxygen through electrolysis , a great challenge.