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The Moon

Origins of Life
March 21, 2019
Planets: Neptune
March 22, 2019

When one looks at the Moon in the night sky

one can see the battered surface that colliding asteroids and comets

The Moon

Can produce on a planetary body. The impact craters on its surface are so large they can easily be seen with the naked eye from your own backyard.These craters are also a testament to the bombardment that our own planet, Earth, has suffered.

The Earth-Moon system occupies the same part of our solar system, so the Earth was the target of the same swarm of colliding debris that hit the Moon. On Earth, however, we have other geologic processes that constantly destroy clues about this impact history.

Mountain building processes, plate subduction, erosion, volcanism, and other processes cover or consume impact craters. So the record on Earth, limited to ~160 impact craters, is only the surviving trace of the millions of impact cratering events that have affected our planet

In addition to impact craters, one can look at the Moon and see that it is composed of light-colored and darker-colored material. The light-colored material is in areas of the Moon called the highlands, which represent the earliest crust on the Moon.

Impact cratering shattered this crust and often deformed it, pushing some of it into mountain-high impact crater rims or ejecting it across the surface of the Moon. This early crust of the Moon was dominated by a type of rock called anorthosite, which is dominated by the white mineral anorthite or plagioclase.

When the Moon was relatively young, its interior was still molten. Consequently, magma sometimes rose and erupted onto the surface. Because the bottoms of impact basins were often the lowest places on the surface of the Moon, the erupting lava would flow into them and begin to fill them. The lava was similar to the basalt that erupts on Earth and, like on Earth, cooled to form a relatively dark-colored rock.

For that reason, some of the largest impact crater basins are outlined by a ring of white mountains (the rim of the crater) and have floors of darker-colored basalt that flooded the craters. Likening the flooding lavas to the seas of Earth, astronomers call the vast plains of basalt mare (singular) or maria (plural) on the Moon.

We have samples of the rock and dust that cover the surface of the Moon. Apollo astronauts with the American space program collected and returned 381.69 kg of samples. The robotic Luna spacecraft built by the Soviet Union also collected and returned 300 g of samples.

The Apollo samples and Luna samples were exchanged between scientists in these countries and other countries around the world so that they could begin deciphering the history of the Moon.

Lunar Sample Collection Sites

Samples from a larger part of the Moon also fall to Earth in the form of meteorites. Lunar meteorites are produced when an asteroid or comet hits the Moon and ejects rocky fragments into an orbit that collides with Earth. These meteorites have shown us new things about the Moon and allowed us to test some of the hypotheses developed from the Apollo and Luna missions.

The brightest and largest object in our night sky, the Moon makes Earth a more livable planet by moderating our home planet's wobble on its axis, leading to a relatively stable climate. It also causes tides, creating a rhythm that has guided humans for thousands of years. The Moon was likely formed after a Mars-sized body collided with Earth.

Ten Things to Know About Earth's Moon

Small Companion If you set a single green pea next to U.S. nickel, you'd have a pretty good idea of the size of the Moon compared to Earth

Constant CompanionThe Moon is Earth's only natural satellite. It goes around the Earth at a distance of about 239,000 miles (385,000 kilometers).

Locked Up The Earth and Moon are tidally-locked. Their rotations are so in sync we only see one side of the Moon all the time. Human's didn't see the lunar far side until a Soviet spaecraft flew past in 1959.

Can Stand on It The Moon is a rocky, solid-surface body with much of its surface cratered and pitted from impacts.

Bring a Spacesuit The Moon has a very thin and tenuous atmosphere called an exosphere. It is not breathable.

Moonless The Moon has no moons.

Ringless The Moon has no rings

Many Visitors More than 105 robotic spacecraft have been launched to explore the Moon. It is the only celestial body beyond Earth—so far—visited by human beings.

Potential for Life? The Moon's weak atmosphere and its lack of liquid water cannot support life as we know it.

Moonwalkers Apollo astronauts brought back a total of 842 pounds (382 kilograms) of lunar rocks and soil to Earth. We are still studying them

Fast Fact: Lunar Eclipses

A partial lunar eclipse will be visible in Africa and the Central Pacific on July 16, 2019 (Viewing Guide). During a lunar eclipse, Earth comes between the Sun and the Moon, blocking the sunlight falling on the Moon. There are two kinds of lunar eclipses:

A total lunar eclipse occurs when the Moon and Sun are on opposite sides of Earth.

A partial lunar eclipse happens when only part of Earth's shadow covers the Moon.

NASA Lunar Eclipse Guides: 2011-2020 and 2021-2030.

During some stages of a lunar eclipse, the Moon can appear reddish. This is because the only remaining sunlight reaching the Moon at that point is from around the edges of the Earth, as seen from the Moon's surface. From there, an observer during an eclipse would see all Earth's sunrises and sunsets at once.

Pop Culture

Our lunar neighbor has inspired stories since the first humans looked up at the sky and saw its gray, cratered face. Some observers saw among the craters the shape of a person's face, so stories refer to a mysterious "Man in the Moon."

Hungrier observers compared its craters to cheese and dreamed of an entire sphere made of delicious dairy products. Jules Verne's 1865 novel From the Earth to the Moon is often credited with inspiring real-life rocket pioneers such as Robert Goddard and Hermann Oberth. While the novel is science fiction, Verne made a few interesting and accurate predictions.

The United States would launch the first manned vehicle to go to the Moon. The shape and size of the vehicle would closely resemble the Apollo command/service module spacecraft. The number of men in the crew would be three.

A competition for the launch site would ensue between Florida and Texas which actually was resolved in Congress in the 1960s with Kennedy Space Center as the Flordia launch site and Houston, Texas, as the Mission Control Center.

A telescope would be able to view the progress of the journey. When Apollo 13 exploded, a telescope at Johnson Space Center witnessed the event which happened more than 200,000 miles from Earth.

The Verne spacecraft would use retro-rockets which became a technology assisting Neil Armstrong and his crewmates in their journey to the Moon.

Verne predicted weightlessness although his concept was slightly flawed in thinking it only was experienced at the gravitational midpoint of the journey (when the Moon and Earth gravity balanced).

The first men to journey to the Moon would return to Earth and splash down in the Pacific Ocean just where Apollo 11 splashed down in July of 1969 one hundred and six years after the initial publication of the novel.

The Moon made its film debut in a 1902 black and white silent French film called Le Voyage Dans la Lune (A Trip to the Moon). And a year before astronauts walked on the moon, 2001: A Space Odyssey (1968) told the story of astronauts on an outpost on the moon. Decades later, it is still widely regarded as the best science fiction movie ever made.

In reality, while we do not yet have a Moon colony, spacecraft have left lots of debris on the lunar surface, and astronauts have planted six American flags on the Moon. But that doesn't mean the United States has claimed it; in fact, an international law written in 1967 prevents any single nation from owning planets, stars or any other natural objects in space.

Kid-Friendly Moon

Most of the planets in our solar system—and some asteroids—have moons. Earth has one moon. We call it "the Moon" because for a long time it was the only one we knew about. Many languages have beautiful words for Moon. It is "Luna" in Italian, Latin and Spanish, "Lune" in French, "Mond" in German, and "Selene" in Greek..

Our Moon is like a desert with plains, mountains, and valleys. It also has many craters, holes created when space rocks hit the surface at a high speed. There is no air to breathe on the Moon..

The Moon travels around the Earth in an oval shaped orbit. Scientists think the Moon was formed long, long ago when Earth crashed into a Mars-sized object.We always see the same side of the Moon from Earth. You have to go into space to see the other side.

How the Moon Works

From anyplace on Earth, the clearest thing in the night sky is usually the moon, Earth's only natural satellite and the nearest celestial object (240,250 miles or 384,400 km away). Ancient cultures revered the moon. It represented gods and goddesses in various mythologies -- the ancient Greeks called it "Artemis" and "Selene," while the Romans referred to it as "Luna."

When early astronomers looked at the moon, they saw dark spots that they believed were seas (maria) and lighter regions that they believed was land (terrae). Aristotle's view, which was the accepted theory at the time, was that the moon was a perfect sphere and that the Earth was the center of the universe. When Galileo looked at the moon with a telescope, he saw a different image -- a rugged terrain of mountains and craters..

He saw how its appearance changed during the month and how the mountains cast shadows that allowed him to calculate their height. Galileo concluded that the moon was much like Earth in that it had mountains, valleys and plains. His observations ultimately contributed to the rejection of Aristotle's ideas and the Earth-centered universe model.

Because the moon is so close to the Earth relative to other celestial objects, it's the only one to which humans have traveled and set foot upon. In the 1960s, the United States and Russia were involved in a massive "space race" to land men on the moon..

Both countries sent unmanned probes to orbit the moon, photograph it and land on the surface. In July 1969, American astronauts Neil Armstrong and Edwin "Buzz" Aldrin became the first humans to walk on the moon. During six lunar landing missions from 1969 to 1972, a total of 12 American astronauts explored the lunar surface. .

They made observati­ons, took ­photographs, set up scientific instruments and brought back 842 pounds (382 kilograms) of moon rocks and dust samples. What did we learn about the moon from these historic journeys?

What's on the surface of the moon?

The remainder of the lunar surface consists of the bright highlands, or terrae. Highlands are rough, mountainous, heavily cratered regions. The Apollo astronauts observed that the highlands are generally about 4 to 5 km (2.5 to 3 miles) above the average lunar surface elevation,

while the maria are low-lying plains about 2 to 3 km (1.2 to 1.8 miles) below average elevation. These results were confirmed in the 1990s, when the orbiting Clementine probe extensively mapped the lunar surface.

The moon is littered with craters, which are formed when meteors hit its surface. They may have central peaks and terraced walls, and material from the impact (ejecta) can be thrown from the crater, forming rays that emanate from it. Craters come in many sizes, and you'll see that the highlands are more densely cratered than the maria.

Another type of impact structure is a multi-ringed basin. These structures were caused by huge impacts that sent shockwaves outward and pushed up mountain ranges. The Orientale Basin is an example of a multi-ringed basin.

Besides craters, geologists have noticed cinder cone volcanoes, rilles (channel-like depressions, probably from lava), lava tubes and old lava flows, which indicate that the moon was volcanically active at some point.

The moon has no true soil because it has no living matter in it. Instead, the "soil" is called regolith. Astronauts noted that the regolith was a fine powder of rock fragments and volcanic glass particles interspersed with larger rocks.

Upon examining the rocks brought back from the lunar surface, geologists found the following characteristics:

The maria consisted primarily of basalt, an igneous rock derived from cooled lava.

The highland regions include mostly igneous rocks called anorthosite and breccia

If you compare the relative ages of the rocks, the highland areas are much older than the maria. (4 to 4.3 billion years old versus 3.1 to 3.8 billion years old).

The lunar rocks have very little water and volatile compounds in them (as if they've been baked) and resemble those found in the Earth's mantle


The oxygen isotopes in moon rocks and the Earth are similar, which indicates that the moon and the Earth formed at about the same distance from the sun.

The density of the moon (3.3 g/cm3) is less than that of the Earth (5.5 g/cm3), which indicates that it doesn't have a substantial iron core.

Astronauts placed other scientific packages on the moon to collect data:

Seismometers didn't detect any moonquakes or other indications of plate tectonic activity (movements in the moon's crust) Magnetometers in orbiting spacecraft and probes didn't detect a significant magnetic field around the moon, which indicates that the moon doesn't have a substantial iron core or molten iron core like the Earth does.

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