moon missions

8/3/2019 Moon Missions

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Moon

I INTRODUCTION

Landmarks of the MoonThis view of the full moon shows its dark seas, or maria, and the two bright-rayed craters Tycho (near bottom) and

Copernicus (directly north of Tycho). The main seas are the Oceanus Procellarum (far left), Mare Imbrium (top

center), Mare Crisium (far right), Mare Tranquillitatis (directly left of Crisium), Mare Serenitatis (above

Tranquillitatis), and Mare Fecundatis (beneath and right of Tranquillitatis).

John Sanford/Science Source/Photo Researchers, Inc.

Moon, name given to the only natural satellite of Earth. The Moon is the second brightest object in

Earths sky, after the Sun, and has accordingly been an object of wonder and speculation for people

since earliest times. The natural satellites of the other planets in the solar system are also sometimes

referred to as moons.

Telescopes have revealed a wealth of lunar detail since their invention in the 17th century, and

spacecraft have contributed further knowledge since the 1950s. Earths Moon is now known to be a

slightly egg-shaped ball composed mostly of rock and metal. It has no liquid water, virtually no

atmosphere, and is lifeless. The Moon shines by reflecting the light of the Sun. Although the Moon

appears bright to the eye, it reflects on average only 12 percent of the light that falls on it. This

reflectivity, called albedo, of 0.12 is similar to that of coal dust.

The diameter of the Moon is about 3,480 km (about 2,160 mi), or about one-fourth that of Earth. The

Moons mass is only 1.2 percent of Earths mass. The average density of the Moon is only three-fifths

that of Earth, and gravity at the lunar surface is only one-sixth as strong as gravity at sea level on

Earth. The Moon moves in an elliptical (oval-shaped) orbit around Earth at an average distance of

384,403 km (238,857 mi) and at an average speed of 3,700 km/h (2,300 mph). It completes one

revolution in 27 days 7 hours 43 minutes. For the Moon to go from one phase to the next similar


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phaseas seen from Earthrequires 29 days 12 hours 44 minutes. This period is called a lunar

month. The Moon rotates once on its axis in the same period of time that it circles Earth, accounting

for the fact that virtually the same portion of the Moon (the near side) is always turned toward

Earth.

II THE MOON SEEN FROM EARTH

Moon IllusionWhen the moon is close to the horizon, it seems larger than when it is in the sky overhead. Psychologists today still

debate the cause of this illusion, which has fascinated scientists and philosophers for centuries. Here the moon

looms large over the San Francisco skyline.

Michael J. Howell/Liaison Agency

As the Moon orbits Earth in a counterclockwise direction, Earth itself rotates counterclockwise (from

west to east) on its axis and revolves around the Sun in a counterclockwise orbit. All of these motions

combined determine when and how the Moon appears in the sky to an observer on Earth. Seen from a

single spot on Earth, the Moon rises about 50 minutes later every day. Since the Moon has moved13.8 degrees further in its orbit in 24 hours, the Earth has to turn an extra 13.8 degrees on its axis for

the Moon to rise above the horizon again.

The Moon shows progressively different phases as it moves along its orbit around Earth. Half the Moon

is always in sunlight, just as half of Earth has day while the other half has night. Thus, there is no

permanent dark side of the Moon, which is sometimes confused with the Moons far sidethe side

that always faces away from Earth. The phases of the Moon depend on how much of the sunlit half


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can be seen at any one time. In the phase called the new moon, the near side is completely in

shadow. About a week after a new moon, the Moon is in first quarter, resembling a luminous half-

circle; another week later, the full moon shows its fully lighted near side; a week afterward, in its last

quarter, the Moon appears as a half-circle again. The entire cycle is repeated each lunar month. The

Moon is full when it is farther away from the Sun than Earth; it is new when it is closer. When it is

more than half illuminated, it is said to be in gibbous phase. When it is less than half illuminated, it is

said to be in crescent phase. The Moon is said to be waning as it progresses from full to new, and to

be waxing as it proceeds from new to full.

The Moon is in the sky about 12 hours a day. At new moon it is in the sky during daylight hours, rising

just after dawn. At full moon it is visible throughout the night, rising at sunset. The phases of the

Moon match its position in the sky. New moon is noticeable when the Moon is close to the western

horizon at sunset. The full moon occurs when the Moon is above the eastern horizon at sunset about

14 days later. The dark phase of the Moon occurs when the Moon is in the daytime sky with its shaded

night side facing Earth. Its unseen presence can be revealed in a spectacular way if the dark Moon

passes directly in front of the Sun. When this happens, the view of the Sun is blocked and the Moons

shadow falls on a small region of the surface of the Earth, an event called a solar eclipse.

By a cosmic coincidence, the apparent sizes of the disk of the Moon and the disk of the Sun are

approximately the same (within about 0.5 of a degree) when seen from Earth. If the Moons orbit lay

exactly in the plane of Earths orbit around the Sun, a solar eclipse would occur somewhere on Earth

every month at new moon. However, the Moons orbit is tilted 5.1 degrees with respect to the plane of

Earths orbit around the Sun. As a result, solar eclipses occur only about 2 to 5 times a year. Partial

eclipses, when the Moon only partially covers the disk of the Sun, happen more often than total

eclipses.

Eclipse Microsoft Corporation. All Rights Reserved.

Another type of eclipse results when Earth comes directly between the Sun and the Moon. Lunar

eclipses happen at full moon about twice a year and are visible over large areas of Earth. The round

shadow of Earth passes over the Moon, giving it a red or copper hue from sunlight filtered through

Earths atmosphere.


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Phases of the MoonThe appearance of the Moon from Earth depends on the relative positions of the Earth, Moon, and Sun. This

illustration shows what the Moon looks like from Earth at different stages of the Moon's orbit.

Microsoft Corporation. All Rights Reserved.

At any one time, an observer on Earth can see only 50 percent of the Moons entire surface. However,

an additional 9 percent can be seen from time to time around the edges because the viewing angle

from Earth changes slightly as the Moon moves through its elliptical orbit. This slight relative motion is

called libration.

III SURFACE OF THE MOON

Early observers of the Moon believed that the dark regions on its face were oceans, giving rise to their

name maria(Latin for seas). This term is still used today although these regions are now known to

be completely dry. The brighter regions were held to be continents. Modern observation and

exploration of the Moon has yielded far more comprehensive and specific knowledge.

The Moon has no movement of wind or water to alter its surface, yet it was geologically active in the

past and is still not totally unchanging. Craters cover the surface, and meteors continue to create new

craters. Micrometeorites also slowly erode surface features and alter the lunar soil. Billions of years

ago volcanic eruptions sculpted large areas of the surface. Volcanic features such as maria, domes

(low, rounded, circular hills), and rilles (channels or grooves) are still discernable. Small amounts of

gas from deep in the Moon may still reach the surface. Scientists have also recently discovered

possible evidence of ice in permanently shadowed areas of the surface. Such ice could have come

from comet impacts.


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A Craters

The Moons surface is covered with craters overlain by a layer of soil called regolith. Nearly all the

craters were formed by explosive impacts of high-velocity meteorites. Billions of years of this

meteorite bombardment ground up the Moons surface rocks to produce the finely divided rock

fragments that compose the regolith. Craters range in size from microscopic to the South Pole-Aitken

Basin, which measures over 2,500 km (1560 mi) in diameter and would nearly span the continental

United States. The highest mountains on the Moon, in the Leibnitz and Doerfel ranges near the south

pole, make up the rim crest of the South Pole-Aitken Basin and have peaks up to 6,100 m (20,000 ft)

in height, comparable to the Himalayas on Earth. At full Moon long bright streaks that radiate from

certain craters can be seen. These streaks are called ray systems. Ray systems are created when

bright material ejected from the craters by meteorites splashes out onto the darker surrounding

surface.

The biggest of the Moons craters were created by the impacts of large remnants from the formationof the planets billions of years ago when the young solar system still contained many such remnants.

Astronomers, however, have directly observed meteorites forming small craters on the Moons

surface. Seismometers operating on the lunar surface have also recorded signals indicating between

70 and 150 meteorite impacts per year, with projectile masses from 100 g to 1,000 kg (4 oz to 2,200

lb). Hence the Moon is still being bombarded by meteorites, although neither as often nor as violently

as in the distant past.

B Volcanic Features

Maria, domes, rilles, and a few craters display indisputable characteristics of volcanic origin. Maria are

plains of dark-colored rock that cover approximately 40 percent of the Moon's visible hemisphere. The

maria formed when molten rock erupted onto the surface and solidified between 3.16 billion and 3.96

billion years ago. This rock resembles terrestrial basalt, a volcanic rock type widely distributed on

Earth, but the rock that formed the maria has a higher iron content and contains unusually large

amounts of titanium. The largest of the maria is Oceanus Procellarum, an oval-shaped plain on the

near side of the Moon 2,500 km by 1,500 km wide.

Photographs of the side of the Moon not visible from Earth have revealed a startling fact: The far side

generally lacks the maria that are so conspicuous a feature of the visible side. This probably reflects

the fact that the Moons crust is thicker on the far side than on the near side, and therefore the lavas

that form the maria were more easily erupted through the thinner crust of the near side.

Rilles are of two basic types: sinuous and straight. Sinuous rilles are meandering channels that are

probably lava drainage channels or collapsed lava tubes formed by large lava flows. Straight rilles are

large shallow troughs caused by movement of the Moons crust; they may be up to a thousand

kilometers long and several kilometers wide.


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Domes are small rounded features that range from 8 to 16 km (5 to 10 mi) in diameter and from 60

to 90 m (200 to 300 ft) in height. Domes, thought to be small inactive volcanoes, often contain a

small rimless pit on their tops.

Magnetic and other measurements indicate a current temperature at the Moons core as high as

1600C (2900F), above the melting point of most lunar rocks. Evidence from seismic recordings

suggests that some regions near the lunar center may be liquid. However, no recent eruptions of

liquid rock have been observed and the Moon evidently has had no volcanic activity on its surface over

the last 1 billion years. At most, trapped gas from deep in the Moon may still reach the surface in

some places.

Astronomers reported possible evidence of out-gassing on the surface of the Moon in the last 1 to 10

million years in a paper published in 2006. The unusually bright soil around a feature 3 km (2 mi)

wide on the Moons equator indicates some process has turned over fresh regolith that has not had

enough time to be weathered by solar wind and micrometeorites. Called Ina, the feature was first

photographed from Apollo spacecraft orbiting the Moon in the 1970s, and was later examined by theClementine probe. Gases from inside the Moon may have erupted on the surface, lifting and exposing

fresh lunar soil. Scientists do not know the exact source and nature of the gases. At least three other

lunar features that look similar to Ina have been identified. They may have been formed by bursts of

gas, as well.

C Ice

Temperatures on most of the Moons surface are too extreme for water or ice to exist, ranging from a

maximum of 127C (261F) at lunar noon to a minimum of -173C (-279F) just before lunar dawn.

Temperatures in permanently shadowed areas near the lunar poles, however, may consistently be as

low as -220C (-364F). Comets and micrometeoroids that strike the Moon release gases that contain

water. The gases would form an extremely thin atmosphere that would then migrate to the coldest

regions of the poles and condense out, forming ice that combines with the lunar

soil. In 1996 a team working with data gathered by the Clementine spacecraft announced that frozen

water may exist in one of these shadowed areas near the Moons south pole. Clementine was a joint

venture by the Department of Defense and the National Aeronautics and Space Administration

(NASA). The spacecrafts radar showed what may be an 8,000 sq km (3,000 sq mi) area covered with

a mixture of dirt and ice crystals. Clementine was launched in 1994 and gathered data for four

months.

NASA launched the Lunar Prospector spacecraft toward the Moon in 1998. Prospector returned data

that appeared to confirm the Clementine discovery and suggested that a significant amount of water

exists in the dark areas near the lunar poles in the form of ice crystals mixed with soil. The evidence

was indirect, however, and consisted of finding elevated levels of hydrogen, a component of water,

around the poles. Estimates of the possible amount of water on the Moon varied widely, from 10

million to 6 billion metric tons.


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In 1999, at the end of the Lunar Prospectors mission, scientists programmed the spacecraft to crash

at a specific spot likely to contain water, hoping that the debris that rose with the impact would

contain detectable water vapor. Although no water was detected after the crash, scientists could not

conclude that no water existed on the Moon. They acknowledged several other possible explanations

for the result: The spacecraft might have missed its target area, the telescopes used to observe the

crash might have been aimed incorrectly, or the magnitude of the impact created by the Lunar

Prospector spacecraft may have been insufficient to generate a large cloud of water vapor.

In 2003 researchers used the giant Arecibo Observatory radio telescope to bounce radar signals off

the surface of craters at the Moons poles. The returned radar signal indicated that large, thick layers

of ice were not present. The findings failed to rule out the existence of smaller amounts of ice at the

lunar poles preserved in thin layers or as scattered ice crystals mixed with dust. The Arecibo

Observatory conducted a higher resolution radar study of the lunar south pole in 2006 and found that

similar radar signals came from both sunlit and shaded areas. The issue of ice at the lunar poles was

not resolved, however. NASAs Lunar Reconnaissance Orbiter (LRO), scheduled for launch in 2008, will

carry a special satellite called LCROSS (Lunar CRater Observation and Sensing Satellite) that will look

for evidence of water in the debris plume when the LROs booster stage crashes into Shackleton Crater

at the south pole.

IV ORIGIN OF THE MOON

Measuring the ages of lunar rocks has revealed that the Moon is about 4.6 billion years old, or about

the same age as Earth and probably the rest of the solar system. Before the modern age of space

exploration, scientists had three major models for the origin of the Moon. The fission from Earth model

proposed that the young, molten Earth rotated so fast that it flung off some material that became the

Moon. The formation in Earth orbit model claimed that the Moon formed independently, but close

enough to Earth to orbit the planet. The formation far from Earth model proposed that the Moon

formed independently in orbit around the Sun but was subsequently captured by Earths gravity when

it passed close to the planet. None of these three models, however, is entirely consistent with current

knowledge of the Moon. In 1975, having studied Moon rocks and close-up pictures of the Moon,

scientists proposed what has come to be regarded as the most probable of the theories of formation:

a giant, planetary impact.

The giant impact model proposes that early in Earths history, well over 4 billion years ago, Earth was

struck by a large planet-sized body sometimes referred to as Theia. Early estimates for the size of this

object were comparable to the size of Mars, but other research suggests that the object may have

been more massive and that it struck Earth at a glancing angle. The catastrophic impact blasted

portions of Earth and the impacting body into Earths orbit, where debris from the impact eventually

coalesced to form the Moon. After years of research on lunar rocks during the 1970s and 1980s, this

model became the most widely accepted one for the Moons origin.


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The giant impact model seems to account for most of the available evidence: the similarity in

composition between Earth and Moon indicated by analysis of lunar samples, the near-complete global

melting of the Moon (and possibly Earth) in the distant past, and the simple fact that the other models

are all inadequate to one degree or another. Research continues on the ramifications of such a violent

lunar origin to the early history of Earth and the other planets.

Similar giant impacts may have affected the planets Mercury and Venus, but without forming moons

at least none that have survived. Mercury may have had most of its outer crust blasted away, leaving

a dense iron core. Venuss slow backward (retrograde) rotation may have been caused by one or more

collisions with planet-sized bodies.

V MAGNETIC PROPERTIES OF THE MOON

The Moon has no global magnetic field as does Earth. Some lunar rocks are weakly magnetic,

indicating that they solidified in the presence of a magnetic field. The Moon has small, local magneticfields that seem to be strongest in areas that are on opposite hemispheres from large basins. The

origin of these local magnetic fields is unknown. Some scientists speculate that the magnetic fields

were induced by the extreme shock pressures associated with the large asteroid collisions that created

the basins. Others believe that the Moon originally had a global magnetic field generated by the

movement of liquid metal in the core as on Earth. This global field shut down for some reason and

only remnants of it exist in certain places on the lunar surface, preserved in material ejected by the

asteroid collisions. The fossil magnetism found in some lunar rocks supports the former global field

model, whereas the regional distribution of the magnetic surface anomalies tends to support the local

field model. Regions of strong magnetic fields repel the charged particles that stream from the Sun in

the solar wind. Scientists believe that interaction with the solar wind darkens the Moon, and that some

lighter swirl-shaped regions of the Moon are protected by local magnetic fields.

VI GRAVITATIONAL INFLUENCE OF THE MOON

The Moon orbits the Earth because of the force of Earths gravity. However, the Moon also exerts a

gravitational force on the Earth. Evidence for the Moons gravitational influence can be seen in the

ocean tides. The Moon, being much nearer to the Earth than the Sun, is the principal cause of tides.

Because the force of gravity decreases with distance, the Moon exerts a stronger gravitational pull on

the side of the Earth that is closer to it and a weaker pull on the side farther from it. The Earth does

not respond to this variation in strength because the planet is rigidinstead, it moves in response to

the average of the Moons gravitational attraction. The worlds oceans, however, are liquid and can

flow in response to the variation in the Moons pull. On the side of the Earth facing the Moon, the

Moons stronger pull makes water flow toward it, causing a dome of water to rise on the Earths

surface directly below the Moon. On the side of the Earth facing away from the Moon, the Moons pull

on the oceans is weakest. The waters inertia, or its tendency to keep traveling in the same direction,

makes it want to fly off the Earth instead of rotate with the planet. The Moons weaker pull does not


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compensate as much for the waters inertia on the far side, so another dome of water rises on this

side of the Earth. The dome of water directly beneath the Moon is called direct tide, and the dome of

water on the opposite side of the Earth is called opposite tide.

As the Earth rotates throughout the day, the domes of water remain aligned with the Moon and travel

around the globe. When a dome of water passes a place on the Earth, that place experiences a rise in

the level of the ocean water, known as high tide or high water. Between successive high tides the

water level drops. The lowest water level reached between successive high tides is known as low tide

or low water. Low and high tides alternate in a continuous cycle. The variations that naturally occur in

the level between successive high tide and low tide are referred to as the range of tide. At most

shores throughout the world, two high tides and two low tides occur every lunar day, the average

length of a lunar day being 24 hours, 50 minutes, and 28 seconds. One of these high tides is caused

by the direct-tide dome and the other by the opposite-tide dome. Two successive high tides or low

tides are generally of about the same height.

VII LUNAR EXPLORATION

Luna LanderMissions 9 and 13 of the Soviet Luna program landed on the moon, then released a small capsule. The capsule had

a weighted base, so it rolled upright. It then opened its flaps, exposing a television camera and communications

antennas.


Throughout the 19th and 20th centuries, visual exploration with powerful telescopes yielded fairly

comprehensive knowledge of the geography of the visible side of the Moon. The hitherto unseen far

side of the Moon was first revealed to the world in October 1959 through photographs made by the

Soviet Luna 3 spacecraft. These photographs showed that the far side of the Moon is similar to the

near side except for the absence of large maria. Craters are now known to cover the entire Moon. In


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1964 and 1966 photographs from U.S. spacecraftRanger 7 through 9 and Lunar Orbiter 1 through

5further supported these conclusions. The entire Moon has about 3 trillion craters larger than 1 m (3

ft) in diameter.

The successful landings of the robotic U.S. Surveyor series spacecraft and the USSR Luna series in the

1960s, and then the manned landings on the lunar surface as part of the U.S. Apollo program, made

direct measurement of the physical and chemical properties of the lunar surface a reality (seeSpace

Exploration). The Apollo astronauts collected rocks, took thousands of photographs, and set up

instruments on the Moon that radioed information back to Earth even after the astronauts departed.

These instruments measured temperature and gas pressure at the lunar surface; heat flow from the

Moons interior; molecules and ions of hot gases, called the solar wind, that stream out from the

atmosphere of the Sun; the Moons magnetic field and gravity; seismic vibrations of the lunar surface

caused by landslides, meteorite impacts, and so-called moonquakes; and the precise distance between

Earth and the Moon.

Traveling to the Moon and BackThe Apollo 11 mission to the Moon involved a complicated, carefully timed series of stages, as shown here. The

journey to the Moon is shown as a yellow line, while the return trip is indicated by a blue line. Space travel would

be impossible without precise mathematical calculations of acceleration, distance, gravitational pull, friction, and so

on.


All six manned landings on the MoonApollo 11, 12, 14, 15, 16, and 17returned samples of rock

and soil to Earth. These samples weighed a total of 384 kg (847 lb). The astronauts explored

increasingly wider areas on the Moon with each successive flight, culminating with the 35 km (22 mi)

explored using a lunar roving vehicle by the Apollo 17 crew. This final mission included the only

geologist ever to walk on the Moon, Harrison (Jack) Schmitt. Analysis of the data and rocks obtained

by the lunar missions continues.


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Earth from the MoonIn the late 1960s, people saw for the first time what Earth looked like from space. This famous photo of Earth was

taken by astronauts on the Apollo 8 mission as they orbited the Moon in 1968.

NASA

In 1994, the joint Defense Department/NASA spacecraft Clementine orbited the Moon for 71 days,

mapping the color and precise altitude of the lunar surface. From Clementine data, astronomers

obtained their first global look at the topography and mineralogy of the Moon, finding that the Moons

crust is indeed made of a low-iron, low-density rock called anorthosite and mapping the large, ancient

basins that make up the structural framework of the Moon. Clementine also discovered possible

evidence of ice on the Moon in the permanently dark areas near the south pole.

NASA sent a spacecraft of its own, an orbiter called Lunar Prospector, to the Moon in 1998. Lunar

Prospector orbited around the Moons north and south poles and returned data until July 1999. The

spacecraft mapped the gravitational field of the Moon, determined the distribution of radioactive

elements in its crust, and found additional evidence that could indicate the presence of ice at the lunar

poles. Scientists used the spacecraft right up to its final moments. They ended Prospectors mission by

programming it to crash into the Moons surface and then observed the cloud of debris that rose from

the impact.


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First Steps on the MoonApollo 11 crewmen Neil A. Armstrong and Edwin E. Aldrin, Jr., took their first historic steps on the moon on July

20, 1969. Armstrong is shown here stepping off the lunar module (LM). Aldrin followed him 20 minutes later.

During their 2 hours 31 minutes outside the LM, the two men planted the United States flag, collected 22 kg (49 lb)

of lunar rocks and soil, and deployed scientific equipment to study the solar wind and measure seismic tremors inthe moon's interior and on its surface.

Archive Films

In 2003 the European Space Agency (ESA) launched it first lunar probe, called SMART-1 (Small

Missions for Advanced Research and Technology). The solar-powered orbiter used an innovative form

of ion propulsion. It carried a number of instruments to study the chemical elements that make up the

Moons surface. At the end of its mission in 2006, the probe was deliberately crashed into the lunar

surface. Earth-based telescopes studied the composition of the debris thrown up by the impact.

Lunar LandscapeDuring the Apollo 17 mission in 1972, astronauts explored the rugged Taurus-Littrow region of the moon, shown

here. The astronauts spent 22 hours touring 35 km (22 mi) of the area in a lunar rover. In addition, they collected


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more than 109 kg (243 lb) of rock samples for scientific analysis. The Apollo 17 mission was the last lunar flight

with a crew.

NASA

An ambitious series of international Moon probes have been planned. Chinas first Moon probe, the

lunar orbiter Change No. 1 (pronounced CHAHNG-UH), was launched in 2007. It is named for the

fairy maiden Change, who traveled to the Moon in Chinese mythology. Based on the design of the

Dongfanghong-3 communications satellite, the Chinese probe will send back photos and data about

the Moon. The Chinese are working with Russian experts to build a robot Moon lander for launch by

2010.

Indias first Moon mission, called Chandrayaan-1 (pronounced CHUN-dry-ahn, meaning Moon craft in

Sanskrit), is scheduled for launch in 2008. The orbiting probe will carry European scientific

instruments and two instruments provided by NASA, the M3 (Moon Mineralogy Mapper) and the Mini

SAR (Mini Synthetic Aperture Radar). M3(pronounced em cube) is a highly advanced imaging

spectrometer designed to map the entire lunar surface to study its mineral composition. Mini SAR is an

imaging radar device designed to map the lunar poles and look for water ice. It will see into

permanently shadowed areas at the poles and can distinguish the radar signature of ice from surface

roughness.

Japan launched its SELENE (SELenological and ENgineering Explorer) moon probe in 2007. The orbiter

will map the Moon and deploy a small satellite to study the gravitational field on the far side of the

Moon. The orbiters propulsion unit will later separate and land on the lunar surface.

NASA has proposed a series of unmanned Moon probes over the next decade, leading to a manned

landing by 2020. The Lunar Reconnaissance Orbiter is slated for launch in 2008, carrying six different

instruments. Also on board will be a small, separate satellite called LCROSS (Lunar CRaterObservation and Sensing Satellite). The main probe will map small areas ofthe Moons surface in high

resolution. The upper stage of the probes booster rocket will impact Shackleton Crater at the south

pole, sending up a plume of debris that could reveal water ice. The LCROSS satellite will study the

plume for signs of ice then crash into the crater itself, creating a second impact for observers on

Earth. Possible future missions may include sample returns from the lunar surface.

The first step toward a return to manned exploration of the Moon came in 2006 with NASAs official

announcement of the design and contractor for the Orion space capsule, part of the Constellation

program of manned space flights. Plans call for a lunar landing in 2020, with an unmanned cargo

mission in 2019. A crew of four will reach the Moon in an Orion capsule accompanied by a lunar

lander. The four astronauts will land on the surface and spend about a week on the Moon. By 2024 a

permanent Moon base may be established, probably near the lunar south pole. China has also

announced plans for manned flights to the Moon for sometime after 2020.

Although much has been learned about the Moon in the past few decades, much still remains

mysterious. Understanding the Moon and its history is important for two reasons. First, the Moon is a

natural laboratory to study the geological processesmeteorite impacts, volcanism, and large-scale


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movements of the crustthat have shaped all of the rocky planets. Second, the Moons ancient

surface retains a record of events in this part of the solar system that has been erased from the much

more active, dynamic surface of Earth. The impact record, which has been almost entirely erased on

Earth, is especially clear on the Moon, and may contain important clues to the history of life on Earth.

Thus, the Moon serves as a touchstone, allowing us to better comprehend the complex stories of all

the planets in our solar system.

Reviewed By:

Paul D. SpudisMicrosoft Encarta 2009. 1993-2008 Microsoft Corporation. All rights reserved.

moon missions

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