Introduction Origin and Evolution the Exosphere And

8/14/2019 Introduction Origin and Evolution the Exosphere And

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The Moon

Introduction

Origin and evolution

The exosphere and surface features

Interior

Recent exploration


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Introduction

The moon's average radius is 1,079.6 miles, about 27 percent of the radius of Earth.

The moon's density is about 3.34 grams per cubic centimeter, roughly 60 percent of

Earth's density.

The temperature at the lunar equator ranges from extremely low to extremely high --

from about -173 degrees C at night to +127 degrees C in the daytime. In some deep

craters near the moon's poles, the temperature is always near -240 degrees C. Many craters in the terrain exceed 25 miles in diameter. The largest is the South

Pole-Aitken Basin, which is 1,550 miles in diameter.

The dark areas on the moon are known as maria (MAHR ee uh). The word maria is

Latin for seas; its singular is mare (MAHR ee). The term comes from the smoothness

of the dark areas and their resemblance to bodies of water. The maria are cratered

landscapes that were partly flooded by lava when volcanoes erupted. The lava then

froze, forming rock.

In 1959, scientists began to explore the moon with robot spacecraft. In that year, the

Soviet Union sent a spacecraft called Luna 3 The word luna is Latin for moon.


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On July 20, 1969, the U.S. Apollo 11 lunar module landed on the moon in the first of six Apollo

landings. Astronaut Neil A. Armstrong became the first human being to set foot on the moon.

In the 1990's, two U.S. robot space probes, Clementine and Lunar Prospector, detected

evidence of frozen water at both of the moon's poles. The ice came from comets that hit the

moon over the last 2 billion to 3 billion years. The ice apparently has lasted in areas that are

always in the shadows of crater rims. Because the ice is in the shade, where the temperature is

about -240 degrees C, it has not melted and evaporated.

. A slight motion called libration enables us to see about 59 percent of the moon's surface at

different times.


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Origin and evolution of the moon

The moon formed as a result of a collision known as the Giant Impact or the "Big

Whack." " According to this idea, Earth collided with a planet-sized object 4.6 billion years ago.

As a result of the impact, a cloud of vaporized rock shot off Earth's surface and went

into orbit around Earth. The cloud cooled and condensed into a ring of small, solid

bodies, which then gathered together, forming the moon.

As the crust formed, asteroids bombarded it heavily, shattering and churning it. The

largest impacts may have stripped off the entire crust. Some collisions were so

powerful that they almost split the moon into pieces. One such collision created the

South Pole- Aitken Basin, one of the largest known impact craters in the solar

system.

About 4 billion to 3 billion years ago, melting occurred in the mantle, probably causedby radioactive elements deep in the moon's interior. The resulting magma erupted as

dark, iron-rich lava, partly flooding the heavily cratered surface. The lava cooled and

solidified into rocks known as basalts (buh SAWLTS).


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Impacts of large objects can create craters. Impacts of micrometeoroids (tiny meteoroids) grind

the surface rocks into a fine, dusty powder known as the regolith (REHG uh lihth). Regolith

overlies all the bedrock on the moon. Because regolith forms as a result of exposure to space,

the longer a rock is exposed, the thicker the regolith that forms on it.


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The exosphere and surface features of the moon

The lunar exosphere -- that is, the materials surrounding the moon that make up the

lunar "atmosphere" -- consists mainly of gases that arrive as the solar wind. The solar

wind is a continuous flow of gases from the sun -- mostly hydrogen and helium, along

with some neon and argon.

A continual "rain" of micrometeoroids heats lunar rocks, melting and vaporizing their

surface. The most common atoms in the vapor are atoms of sodium and potassium.

Those elements are present in tiny amounts -- only a few hundred atoms of each percubic centimeter of exosphere. In addition to vapors produced by impacts, the moon

also releases some gases from its interior .

The vast majority of the moon's craters are formed by the impact of meteoroids,

asteroids, and comets. Craters on the moon are named for famous scientists. For

example, Copernicus Crater is named for Nicolaus Copernicus, a Polish astronomer

who realized in the 1500's that the planets move about the sun. Archimedes Crater isnamed for the Greek mathematician Archimedes, who made many mathematical

discoveries in the 200's B.C.


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Surrounding the craters is rough, mountainous material -- crushed and broken rocks that were

ripped out of the crater cavity by shock pressure. This material, called the crater ejecta blanket,

can extend about 60 miles from the crater.

Basins are craters that are 190 miles or more across. The smaller basins have only a single

inner ring of peaks, but the larger ones typically have multiple rings. The rings are concentric --

that is, they all have the same center, like the rings of a dartboard. The spectacular, multiple-

ringed basin called the Eastern Sea (Mare Orientale) is almost 600 miles across. Other basinscan be more than 1,200 miles in diameter -- as large as the entire western United States.

Rilles are snakelike depressions that wind across many areas of the maria. Scientists formerly

thought the rilles might be ancient riverbeds. However, they now suspect that the rilles are

channels formed by running lava. One piece of evidence favoring this view is the dryness of

rock samples brought to Earth by Apollo astronauts; the samples have almost no water in their

molecular structure. . One of the largest concentrations of cones on the moon is the Marius Hills complex in

Oceanus Procellarum (Ocean of Storms). Within this complex are numerous wrinkle ridges and

rilles, and more than 50 volcanoes.


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The interior of the moon

The moon has three interior zones -- crust, mantle, and core.

Most of what scientists know about the moon has been learned by studying seismicevents - moonquakes. The data on moonquakes come from scientific equipment set upby Apollo astronauts from 1969 to 1972.

The average thickness of the lunar crust is about 43 miles, compared with about 6 milesfor Earth's crust. The outermost part of the moon's crust is broken, fractured, and jumbledas a result of the large impacts it has endured. This shattered zone gives way to intactmaterial below a depth of about 6 miles. The bottom of the crust is defined by an abruptincrease in rock density at a depth of about 37 miles on the near side and about 50 mileson the far side.

The mantle of the moon consists of dense rocks that are rich in iron and magnesium. Themantle formed during the period of global melting. Low-density minerals floated to theouter layers of the moon, while dense minerals sank deeper into it.

Later, the mantle partly melted due to a build-up of heat in the deep interior. The sourceof the heat was probably the decay of uranium and other radioactive elements. Thismelting produced basaltic magmas -- bodies of molten rock. The magmas later madetheir way to the surface and erupted as the mare lavas and ashes. Although marevolcanism occurred for more than 1 billion years -- from at least 4 billion years to fewerthan 3 billion years ago -- much less than 1 percent of the volume of the mantle everremelted.


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Data gathered by Lunar Prospector confirmed that the moon has a core and enabled scientists

to estimate its size. The core has a radius of only about 250 miles. By contrast, the radius of

Earth's core is about 2,200 miles.

If the core of a planet or a satellite is molten, motion within the core caused by the rotation of

the planet or satellite makes the core magnetic. But the small, partly molten core of the moon

cannot generate a global magnetic field.

The presence of vesicles in lunar basalt indicates that the deep interior contained gases,

probably carbon monoxide or gaseous sulfur. The existence of volcanic ash is further evidence

of interior gas; on Earth, volcanic eruptions are largely driven by gas.


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Recent Exploration

The United States sent the orbiter Clementine in 1994.A laser device measured the

height and depth of mountains, craters, and other features. Radar signals that

Clementine bounced off the moon provided evidence of a large deposit of frozen

water. The ice appeared to be inside craters at the south pole.

The U.S. probe Lunar Prospector orbited the moon from January 1998 to

July 1999. The craft mapped the concentrations of chemical elements in themoon, surveyed the moon's magnetic fields, and found strong evidence of

ice at both poles. Small particles of ice are apparently part of the regolith at

the poles.

The SMART-1 spacecraft, launched by the European Space Agency in

2003, went into orbit around the moon in 2004. The craft's instruments were

designed to investigate the moon's origin and conduct a detailed survey ofthe chemical elements on the lunar surface.


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M3 and Indias First Mission to Moon The Moon Mineralogy Mapper (M3) is one of two instruments that NASA is contributing to India's

first mission to the Moon, Chandrayaan-1 (meaning "Lunar Craft" in ancient Sanskrit), whichlaunched on October 22, 2008. M3 is a state-of-the-art imaging spectrometer that will provide thefirst map of the entire lunar surface at high spatial and spectral resolution, revealing the mineralsof which it is made.

Scientists will use this information to answer questions about the Moon's origin and developmentand the evolution of terrestrial planets in the early solar system. Future astronauts will use it tolocate resources, possibly including water, that can support exploration of the Moon and beyond.


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This image of the moon is from NASA's Moon

Mineralogy Mapper on the Indian Space Research

Organization's Chandrayaan-1 mission. It is a

three-color composite of reflected near-infrared

radiation from the sun, and illustrates the extent to

which different materials are mapped across theside of the moon that faces Earth.

Small amounts of water and hydroxyl (blue) were

detected on the surface of the moon at various

locations. This image illustrates their distribution at

high latitudes toward the poles.

Blue shows the signature of water and hydroxyl

molecules as seen by a highly diagnostic

absorption of infrared light with a wavelength of

three micrometers. Green shows the brightness of

the surface as measured by reflected infraredradiation from the sun with a wavelength of 2.4

micrometers, and red shows an iron-bearing

mineral called pyroxene, detected by absorption of

2.0-micrometer infrared light.


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These images from NASA's Moon

Mineralogy Mapper on the Indian

Space Research Organization's

Chandrayaan-1 spacecraft show data

for the hemisphere of the moon that

faces Earth. The image on the leftshows albedo, or the sunlight reflected

from the surface of the moon. The

image on the right shows where

infrared light is absorbed in the

characteristic manner that indicates the

presence of water and hydroxylmolecules. That image shows that

signature most strongly at the cool,

high latitudes near the poles. The blue

arrow indicates Goldschmidt crater, a

large feldspar-rich region with a higher

water and hydroxyl signature.


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These images show a very

young lunar crater on the

side of the moon that faces

away from Earth, as viewed

by NASA's MoonMineralogy Mapper on the

Indian Space Research

Organization's

Chandrayaan-1 spacecraft.

On the left is an image

showing brightness at

shorter infrared

wavelengths. On the right,

the distribution of water-rich

minerals (light blue) is

shown around a small

crater. Both water- and

hydroxyl-rich materials werefound to be associated with

material ejected from the

crater.


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Images taken at wavelengths not

visible or discernable to the human

eye are assigned colors, revealing the

invisible "colors" of the moon. While

our eyes are sensitive to wavelengthsfrom about 0.4 to 0.75 micrometers,

the Moon Mineralogy Mapper

measured energy from the moon from

0.45 through 3 micrometers, well into

the infrared portion of the light

spectrum. The instrument has a

spectrometer that splits the

wavelength range into 86 images, orbands, in one mode, and 260 bands in

its higher-resolution mode.

The animation takes a random walk

through the data, with various

combinations of images systematically

assigned colors of red, green andblue. Different colors show various

minerals and water on the surface of

the moon. This is a sampling of just

some of the data -- more information is

contained in the whole Moon

Mineralogy Mapper data set.


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This is an early mineral map derived from the

different reflected light, or spectral,

signatures, measured by NASA's Moon

Mineralogy Mapper on board the Indian

Space Research Organization's

Chandrayaan-1 spacecraft. The green, purple

and blue areas are covered with iron-rich lava

flows. These are similar to the lava flows of

Hawaii. The red and pink regions contain the

mineral plagioclase. Plagioclase is one of the

minerals found in granite rocks on Earth, such

as the granite of Yosemite National Park.


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References

http://www.nasa.gov

http://m3.jpl.nasa.gov/NEWS/
http://m3.jpl.nasa.gov/NEWS/http://m3.jpl.nasa.gov/NEWS/

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