The Moon of Earth

The Moon or Luna is the only natural satellite of Earth and with a diameter of 3,476 km is the second largest moon relative to its primary in the Solar System.
The Moon’s surface is composed of old heavily cratered mountainous highlands and smooth younger Maria (large impact craters). Everything is covered in a layer of rocky fragments and dust called regolith the end product of a million meteor impacts. The mean surface temperature at the equator is -53 degrees Celsius.

The Moon has a 70 kilometer thick crust below which is a mantle surrounding a small core.

There is a great deal of uncertainty when it comes to the Moon's origin, prevailing theories include: co-accretion in which the Earth and Moon formed together as the solar nebula coalesced, fission a splitting of the Earth and Moon, capture in which the Moon as an independent body is captured on passing by the Earth’s gravity field and a fourth possibility, currently in vogue, the impact theory which hypothesizes that a second large body of planetary size [1] impacted the Earth with enough energy to melt it, the Moon forming when the vaporised rock and debris flung into orbit eventually coalesced into a spherical shape.

The effect on Earth of such a large satellite is wide-ranging, ocean tides being the most obvious; the Moon's gravity causes the Earth’s surface to bulge producing a rising and lowering of the ocean's surface. Gravitational interaction between the two bodies is also slowing the Earth's rotation and raising the Moon's orbit, albeit by minuscule amounts.

The Moon has also had an enormous effect on Earth’s flora and fauna, the tides washing aquatic life onto shore have over millions of years been instrumental in their evolution into land life.
Throughout history the Moon’s effect on both humans and human behavior has been especially profound: the word lunatic describes someone erratic or irresponsible, loony is often applied to a mentally ill person, increases in crime of all types are synonymous with a full moon and the terms Harvest Moon and Hunters Moon describe a period of prolonged light following sunset by which farmers could continue to harvest crops and hunters to track game. Campers today appreciate the extra light of a full moon as do most people who work outdoors at night.

The Moon has always figured prominently in human religions, sometimes female such as Selene or Luna, sometimes male such as Tecciztecatl or Mani.

In literature and music the Moon is often either an integral part or provides the inspiration for great works with stories such as “Trends” by Isaac Asimov, “Preludes to Space” by Arthur C. Clarke or “Winter Moon” a poem by Langston Hughes; in music there is “The Moonlight Sonata,” “Blue Moon” or “The Dark Side of the Moon” an album by Pink Floyd; in film there are movies such as, “Destination Moon” or “The First Men in the Moon“ originally a novel by H. G. Wells. The selections mentioned are obviously just a few of thousands.

The Moon has no appreciable atmosphere, but probes such as Clementine and Lunar Prospector have detected the presence of ice at the its poles, data  confirmed in 2009 by the Lunar Reconnaissance Orbiter. Accessibility to deposits of ice from which fuel, oxygen and water can be easily obtained is a necessity for future human colonization.

The Moon has been visited by more spacecraft than any other solar body. Along with numerous successful missions there were many failed attempts. The following is a list of the more significant, both successful and otherwise:

Pioneer 4 (USA) launched on March 3, 1959, was the first successful flyby of the Moon.

Luna 2 (USSR) was the first spacecraft to impact the Moon, September 14, 1959.

Luna 3 (USSR) launched October 4, 1959, was the first spacecraft to image the Moon’s far side.

Ranger 7 (USA) sent back the first high quality images of the Moon’s surface before crash landing, July 31, 1964.

Ranger 9 (USA) sent back images from the Moon before impacting March 24, 1965. The images were broadcast live on Network television.

Luna 9 (USSR) was the first spacecraft to soft land on the Moon, February 3, 1966.

Luna 10 (USSR) was the first spacecraft to orbit the Moon, April 2, 1966.

Surveyor 1 (USA) launched May 30, 1966, was the first American soft landing on the Moon.

Lunar Orbiter 1 (USA) launched August 10, 1966, imaged potential Apollo landing sites.

Lunar Orbiter 4 (USA) launched May 8, 1967, was the first spacecraft to take pictures of the Moon’s South Pole.

Lunar Orbiter 5 (USA) launched August 7, 1967, mapped a large portion of the Moon’s surface.

Surveyor 5 (USA) launched September 8, 1967, tested the Moon's soil.

Surveyor 6 (USA) launched November 7, 1967, tested the Moon's soil, and established the solidity of its surface.

Surveyor 7 (USA) launched January 7, 1968, tested the Moon's soil and found that many rocks had been molten sometime in the distant past.

Apollo 8 (USA) launched December 21, 1968, carrying astronauts Borman, Lovell and Anders, the first humans to orbit the Moon and return successfully to Earth.

Apollo 10 (USA) launched May 18, 1968, carrying astronauts Stafford, Young and Cernan into lunar orbit where they tested procedures for lunar landing before returning successfully to Earth.

Apollo 11 (USA) launched from the Kennedy Space Center aboard a Saturn V on July 16, 1969, at 9:32 EDT (13:32:00 UTC) carrying astronauts Armstrong, Aldrin and Collins into space. After one and a half Earth orbits the Saturn's third stage placed the still incomplete spacecraft into a moon trajectory with a 16:22:13 UTC trans-lunar injection burn. Approximately 30 minutes later, after final separation from the launch vehicle, the Command/Service pair docked with the Lunar Module and extracted it from the Lunar Module Adapter, the now complete spacecraft continuing moonward, the third stage booster into solar orbit.

On July 20 the Lunar Module (Eagle) separated from the Command Module (Columbia) and descended to the lunar surface, the last few minutes harrowing as low on fuel Armstrong was forced to override the onboard computer, landing manually in Mare Tranquillitatis (the Sea of Tranquility) at 16:17 EDT (20:17:40 UTC).

Upon hearing Armstrong’s calm matter of fact words to Mission Control “Houston, Tranquility Base here. The Eagle has landed,” the world released its collective breath; the dream had become reality.

A few hours later astronauts Armstrong and Aldrin became the first humans to walk on the Moon, Armstrong initiating the event with that now well-known phrase: “That’s one small step for (a) man, one giant leap for mankind.”

After twenty-one and a half hours, carrying film and forty-eight pounds (22 kg) of samples, the intrepid lunar explorers rejoined Collins in orbit before returning to Earth. They splashed down in the Pacific Ocean July 24, 1969, at 12:50 EDT (16:50 UT), the aircraft carrier USS Hornet quickly recovering the Command Module, the crew placed in quarantine.

Apollo 12 (USA) launched November 14, 1969, carrying astronauts Gordon, Conrad and Bean. Gordon and Bean landed and remained on the Moon's surface for thirty-one and a half hours collecting samples before returning to the Command Module and then home on November 24, 1969.

Apollo 13 (USA) launched April 11, 1970, carrying astronauts Swigert, Lovell and Haise. An explosion approximately half way to the Moon put an abrupt end to the mission all resources becoming focused on rescue. Though it was touch and go for awhile, the astronauts using the Lunar Module as a "lifeboat" were eventually returned safely to Earth splashing down on April 17.

Luna 16 (USSR) the first robotic mission to the Moon soft landed in darkness on September 20, 1970. Rock samples were collected and the spacecraft returned to Earth September 24, 1970.

Luna 17 (USSR) soft landed the Lunokhod 1 robot vehicle on the Moon’s surface November 15, 1970. The rover returned over 20,000 television pictures to Earth over a period of eleven months.

Apollo 14 (USA) launched January 31, 1971, carrying astronauts Shepard, Mitchell and Roosa. Shepard and Mitchell landed on the Moon, remaining on the surface for thirty-three hours collecting samples before returning to the Command Module and then home on February 9, 1971.

Apollo 15 (USA) launched July 26, 1971, landed on the Moon July 30, 1971 with astronauts Scott and Irwin while Alfred Warden stayed in orbit. It was the first lander to carry a rover as an aid in exploration; samples were collected from over a wide area. The mission returned to Earth August 7, 1971.

Apollo 16 (USA) launched April 16, 1972, landed on the Moon April 20, 1972, with astronauts Young, Duke and a second rover while Thomas Mattingly stayed in orbit. Samples were collected from over a wide area. The mission returned to Earth April 27, 1972.

Apollo 17 (USA) launched December 7, 1972, landed on the Moon December 11, 1972, with astronauts Cernan, Schmitt and a third rover while Ronald Evans stayed in orbit. Samples were collected from over a wide area. The mission returned to Earth December 19, 1972. The crew of Apollo 17 were the last humans to walk on the Moon.

Luna 21 (USSR) soft landed Lunokhod 2 onto the lunar surface on January 15, 1973. Powered by solar panels and heated by radioactivity the rover took 80,000 pictures over a four month period while traveling over thirty-seven kilometers.

Hiten (Japan) launched January 14, 1990, in an elliptical Earth orbit that enabled it to flyby the Moon ten times. A secondary spacecraft named Hagoromo failed as it attempted to assume lunar orbit. Hiten was testing various technologies to be used on upcoming lunar missions.

Clementine (USA) was a partially successful orbiter launched on April 25, 1994. After fulfilling its primary task of mapping the lunar surface it was to continue on to a rendezvous with the asteroid Geographos but malfunctioning thrusters caused the secondary mission to be scrubbed and after collecting information on the Van Allen belts it lost power in June 1994.

Lunar Prospector (USA) was launched January 7, 1998, with the primary mission of mapping lunar surface composition. In particular it was to look for water ice and minerals in permanently dark polar craters. On July 31, 1999, it was purposefully impacted into a polar crater in an attempt to release water vapor none was observed.

Smart-1 (Europe) an ion powered vehicle was launched on September 27, 2003, as part of a European Space Agency program to develop new types of spacecraft intended for future deep space exploration. Along with testing new and innovative technology its task was to search the lunar surface for frozen water and other chemical elements and perhaps shed some light on the Moon’s origins. After a long and successful mission it was deliberately crashed onto the Moon’s surface September 3, 2006, the hope being that the resulting impact crater would allow analysis of subsurface materials.

Kaguya/Selene (Japan) launched July 14, 2007, was a lunar orbiter with a planned one year mission to measure the Moon’s gravitational and magnetic fields. After successfully completing its mission the Japanese spacecraft was deliberately crashed onto the lunar surface June 10, 2009.

Chang’e-1 (China) launched October 24, 2007. Its main objectives were to produce a three dimensional map of the lunar surface, determine the depth of the Moon’s regolith and measure the abundance of helium-3 a non-radioactive isotope rare on Earth but thought to be abundant on the Moon. [2] On March 1, 2009, the Chinese probe ended its mission, impacting the Moon's surface after a controlled descent the deliberate crash providing data needed for future landings.

Chandrayaan-1 (India) launched on October 22, 2008, was both a lunar orbiter and impactor. The mission's main objective was to survey the lunar surface using topographical, spectroscopic and imaging equipment and in keeping on November 14, 2008, after separating from the orbiter, the impactor was deliberately smashed into the Moon's South Pole near Shackleton crater the detritus analyzed for the presence of water ice.

On September 24, 2009, after reviewing the collected data, Carle Pieters of Brown University confirmed that the Moon Mineralogy Mapper (M3), NASA's contribution to the Chandrayaan-1 mission, had found water on the Moon but emphasized "When we say 'water on the moon,' we are not talking about lakes, oceans or even puddles. Water on the moon means molecules of water and hydroxyl that interact with molecules of rock and dust specifically in the top millimeters of the moon’s surface."

Paul G. Lucey, Hawaii Institute of Geophysics and Planetology, University of Hawaii, later added, however, "there may be much 'wetter' regions to be discovered far from the sites that have been sampled to date" and "Perhaps the most valuable result of these new observations is that they prompt a critical re-examination of the notion that the Moon is dry. It is not."

The Lunar Reconnaissance Orbiter (USA) and the Lunar Crater Observation and Sensing Satellite (LCROSS), using an Atlas V 401 rocket, launched June 18, 2009, from Cape Canaveral Air Force Station. Its primary objectives are an evaluation of possible landing sites and a survey of lunar resources. [3] On Thursday evening October 8, 2009, the mission's spent Centaur upper stage broke away from LCROSS. On Friday morning October 9, 2009, it impacted in Cabeus crater followed four minutes later by LCROSS itself, which, after flying through and examining the residue ejected by the first impact, impacted also. The data gathered by LCROSS and the orbiting Lunar Reconnaissance Orbiter (LRO), after being analyzed to determine if water ice was present, was made public November 13, the answer (adding to findings of previous missions) a resounding yes. Not only is there water on the moon, it's there in significant amounts.

Chang'e-2 (China) launched from Xichang Satellite Launch Center, October 1, 2010, entering a circular 62 mile (100km) high luna orbit approximately five days later. Its mission, part of China's Luna Exploration Program, prepares the way for a possible Chinese manned Moon landing 2024-2030. Its immediate goals were, after being maneuvered into an elliptical orbit with a perilune of 9.3 miles (15 km), to relay back to Earth high-resolution images of the Bay of Rainbows (the planned landing site for Chang'e-3) and confirm and expand upon information gathered by Chang'e-1. Following completion of its primary objectives the spacecraft left lunar orbit for the Earth-Sun L2 Lagrangian point arriving August 2011. In April 2012, Chang'e-2 was moved away from L2 and used to image (December 13) 4179 Toutatis a passing asteroid.

The twin (GRAIL A and B) lunar Gravity Recovery and Interior Laboratory spacecraft (USA) were launched from Cape Canaveral Air Force Station September 10, 2011, aboard a single launch vehicle. Separating shortly after reaching space they arrived at their destination separately, entering lunar orbit on New Year's Eve 2011 and New Year's Day 2012 respectively. For almost a year the two solar powered probes circled the Moon in tandem, their mission to study our satellite from "crust to core" measuring its gravity field in the utmost detail. Hopefully data gathered will help us better understand how the Moon, the Earth and other rocky bodies in the Solar System formed. On December 17, 2012, their low orbit and fuel levels no longer within mission parameters, Ebb and Flow [4] were allowed to impact the Moon the impact site named after recently deceased astronaut Sally Ride a mission collaborator.

The Lunar Atmosphere and Dust Environment Explorer or LADEE (USA) was launched from Walpoles Island on September 6, 2013, at 11:27 p.m. EDT (0327 GMT) aboard a Minotaur V carrier rocket, and following a one-month transit entered lunar orbit on October 6, 2013, at 6:57 a.m. EDT (1057 GMT).

After collecting detailed information about the Moon's tenuous exosphere and the lunar dust environment for 128 days, it finally, its orbit having been gradually degraded, executed a planned impact into the surface sometime between 12:30-1:22 a.m. EDT, Friday, April 18 (9:30 and 10:22 p.m. PDT, Thursday, April 17) at 3,600 miles (5,800 km) per hour.

Chang'e-3 (China) a lunar probe comprising a lander and an unmanned solar powered moon rover called "Yutu" (Jade Rabbit) successfully soft landed on the Moon September 14, 2013, at 1:11 p.m. UTC. The mission, a significant leap forward in China's space program, brings that country a step closer to its stated goal of landing a man on the Moon sometime in the near future

Chang'e-4 (China) a follow-up to Chang'e-3 soft landed on the far side of the Moon on 3 January 2019. The mission, utilizing its own rover (Yutu 2), will attempt to determine the age and composition of the region, as well as develop technologies required for further advancement.

[1] The hypothetical planet, about the size of Mars, has been named Theia after the mythical Greek Titaness who gave birth to the moon goddess Selene.

[2] Helium-3 (He-3) was first found on the Moon in 1969 by visiting Apollo astronauts. Non-polluting and with virtually no radioactive by-products it is being touted by many as the fuel of the future. Used in fusion reactors, 50 tons or 2 shuttle loads would purportedly fulfill all of North America’s energy needs for a year. Estimates are that well over a million tons are to be found on our nearest neighbor’s surface.

[3] As an interesting aside the Lunar Reconnaissance Orbiter (LRO) has also captured and relayed back to Earth images of equipment left behind by the Apollo Moon missions of the late 1960s and early 70s.

[4] A classroom of fourth graders from Emily Dickinson School, Bozeman, Montana, were the winners of a NASA contest to rename the two GRAIL spacecraft. Noting the probes would be studying the Moon's gravity and that the effect of said gravity on the Earth is seen every day in the form of ocean tides they cleverly chose the names Ebb and Flow.

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