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Chapter 28 Minor Bodies of the Solar System
Section 1
Earth’s Moon
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Exploring the Moon
Seven of the planets in our solar system have natural satellites, or moons.
The Apollo space program sent six spacecraft to study the moon.
Scientists were able to gather data about the moon’s weak gravity and its effect on astronauts, as well as data about the moon’s surface
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The Lunar Surface
Any feature of the moon is referred to as lunar. Luna is Latin for “moon”.
The light patches seen on the moon’s surface are called anorthosites.
The darker areas are called maria.
Maria are plains of dark, solidified lava which formed more than 3 billion years ago when lava slowly filled basins that were created by massive asteroids.
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Craters, Rilles, and Ridges
The surface of the moon is covered with craters, rilles, and ridges.
Most of the craters formed when debris struck the moon about 4 billion years ago.
Rilles are long, deep channels that run through the maria. Rilles are thought to be leftover lava channels from the formation of the maria.
The moon’s surface also has several ridges, which are long, narrow elevations of rock that rise out of the surface and criss-cross the maria.
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Regolith
The moon’s surface is very susceptible to meteorite hits because the moon has no atmosphere for protection.
Over billions of years, these meteorites crushed much of the rock on the moon’s surface into a layer of dust and small fragments called regolith.
The depth of regolith on the moon varies from 1 m to 6 m.
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Lunar Rocks
Lunar rocks are igneous, and most rocks near the surface are composed mainly of oxygen and silicon.
Rocks from the lunar highlands are light-colored, coarse-grained anorthosites that contain calcium and aluminum.
Rocks from the maria are fine-grained basalts and contain titanium, magnesium, and iron.
Breccia is found in both maria and the highlands. Lunar breccia formed when meteorites
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The Interior of the Moon
The interior of the moon is less dense than the interior of earth.
Scientists have determined that the moon’s interior is layered by studying seismic information collected during moonquakes.
Like, Earth, the moon has three compositional layers: the crust, the mantle, and the core.
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The Moon’s Crust
The side of the moon that faces Earth is called the near side, while the side of the moon that faces away from Earth is called the far side.
The moon’s crust is thicker on side than the other.
The crust on the near side is about 60 km thick. The crust on the far side is up to 100 km thick.
The difference in thickness was caused by the pull of Earth’s gravity during the formation of the moon.
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The Moon’s Mantle and Core
Beneath the crust is the moon’s mantle. The mantle is thought to be made of rock that is rich in silica, magnesium, and iron.
Scientists think that the moon has a small iron core that has a radius of less than 700 km.
Studies of the core have shown that the moon’s rotation is not uniform and that the core is neither completely solid nor completely liquid.
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The Giant Impact Hypothesis
Most scientists agree that the moon formed in three stages.
The giant impact hypothesis: #1Impact #2 The collision ejected chunks of Earth’s mantle into
orbit around Earth. #3 The debris eventually clumped together to form the
moon.
This hypothesis explains when moon rocks share many of the chemical characteristics of Earth’s mantle.
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Formation of the Moon
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Differentiation of the Lunar Interior
Early in its history, the lunar surface was covered by an ocean of molten rock.
Over time, the densest materials moved toward the center of the moon and formed a small core.
The least dense materials formed an outer crust.
The other materials settled between the core and the outer layer to form the moon’s mantle.
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Meteorite Bombardment
When the moon first formed, it was bombarded with meteorites, creating craters and regolith on the moon’s surface.
About 3 billion years ago, less material struck the lunar surface, and few new craters formed.
Craters that have rays formed during the most recent meteor impacts. During this stage, virtually all geologic activity stopped on the moon.
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Lava Flows on the Moon
After impacts on the moon’s surface foremd deep basins, lava flowed out of cracks, or fissures, in the lunar crust.
This lava flooded the crater basins to form maria.
The presence of maria suggest that fissure eruptions once characaterized the moon.
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Lava Flows on the Moon
Because of the uneven thickness of the moon’s crust, more maria formed on the near side of the moon than on the far side.
Scientist do not yet know how magma formed in the lunar interior or how magma reached the surface because there is no evidence of plate tectonics on the moon.
Some scientists think the magma was formed by the large amount of energy that was produced by the long period of intense meteorite bombardment. Other scientists think radioactive decay of materials may have caused magma to form.
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Chapter 28 Minor Bodies of the Solar System
Section 2
Movement of the Moon
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Movements of the Moon
1. The Earth Moon System2. Lunar & Solar Eclipses3. Phases of the Moon
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Lunar Landing Sites
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The Earth-Moon System
Earth and the moon revolve around each other. Together they form a single system that orbits the sun.
The balance point of the Earth-moon system is located within the Earth’s interior, because Earth’s mass is greater than the moon’s mass.
This balance point is called the barycenter.
The barycenter follows a smooth orbit around the sun.
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The Earth-Moon System
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The Moon’s Elliptical Orbit The orbit is an ellipse, the distance between Earth and
the moon varies over a month’s time.
When the moon is farthest from Earth, the moon is at apogee.
When the moon is closest to Earth, the moon is at perigee.
The Average distance to the moon is about 384,000 km.
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Moonrise and Moonset The moon appears to rise and set at Earth’s horizon
because of Earth’s rotation on its axis.
The moon rises and sets 50 minutes later each night. This happens because of both Earth’s rotation and the moon’s revolution.
While Earth completes one rotation each day, the moon also moves in its orbit around Earth.
It takes 1/29 of Earth’s rotation, or about 50 minutes, for the horizon to catch up to the moon.
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Lunar Rotation The moon’s revolution around Earth and its
rotation on its axis take the same amount of time.
Because the rotation and revolution take the same amount of time, observers on Earth always see the same side of the moon.
The part of the moon illuminated by sunlight changes as the moon orbits Earth.
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The sides of the Moon
The “near” side: The side we see from Earth; smooth with lunar ‘maria’
The “far” side: The side we never see from Earth; highly cratered with extreme coloration changes
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Synchronous Rotation:
The moon takes exactly the same amount of time to orbit Earth as it does to rotate
There is no“dark side” of the Moon.
All locations on the moon experience about 14 days of daylight and 14 days of night.
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Spot Question!
Why are we unable to photograph the far side of the moon from Earth?
The far side of the moon is never visible from Earth, because the moon’s rotation and the moon’s revolution around Earth takes the same amount of time.
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ECLIPSES One of the most striking astronomy events Happen when one object blocks another
- Moon, Sun, Earth Two types: LUNAR eclipse (common) SOLAR eclipse (rare!)
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Eclipse
Bodies orbiting the sun cast long shadows into space.
An eclipse occurs when one body passes through the shadow of another.
Shadows have two parts: the inner, cone-shaped part of the shadow
called the umbra the outer part of the shadow called the
penumbra.
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Solar and Lunar Eclipses
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Solar Eclipses
During a total solar eclipse, the sun’s light is completely blocked by the moon. The umbra falls on the area of Earth that lies directly in line with the moon and the sun.
Outside the umbra, but within the penumbra, people see a partial solar eclipse. The penumbra falls on the area that immediately surrounds
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Effects of Solar Eclipses
The sunlight that is not eclipsed by the moon shows the normally invisible outer layers of the sun’s atmosphere.
This causes what is known as the diamond-ring effect, because the sunlight often glistens like the diamond on a ring.
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Effects of Solar Eclipses
If the moon is at or near apogee during a solar eclipse, the moon’s umbra does not reach Earth. This causes an “annual eclipse” in which a thin ring of sunlight is visible around the outer edge of the moon.
The brightness of this ring prevents observers from seeing the outer layers of the sun’s atmosphere
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Total Solar Eclipse- Sun’s corona (thin, outer gases) is visible- Time to study chromosphere, corona during eclipse
Why do eclipses not happen at everyFULL and NEW moon (2x month!) ?
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Lunar Eclipses A lunar eclipse occurs when Earth is positioned
between the moon and the sun and when Earth’s shadow crosses the lighted half of the moon.
When only part of the moon passes into Earth’s umbra, a partial lunar eclipse occurs.
When the entire moon passes through Earth’s penumbra, a penumbral eclipse
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Time-lapse picture of a total lunar eclipse
Even during a total Lunar eclipse, sunlight is bent around the earth and causes the moon to appear red.
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The orbital planes of Earth/Moon are not exactly aligned 5 degree difference makes eclipses
rare!• solar eclipses: 2-5 a year (half are total)• lunar eclipses: 2-3 a year (half are total)
No More than 7 eclipses can occur in one year.
Normally there are 4 eclipses a year.
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Lunar eclipses can be either total, partial, or annular, depending on the alignment of the Sun, Earth, and Moon.
darkest part of eclipse = umbrapartial eclipse = penumbra
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Solar eclipses also can be either total, partial, or annular, depending on the alignment of the Sun, Earth, and Moon.
darkest part of eclipse = umbrapartial eclipse = penumbra
- umbra will hit Earth on one small area where eclipse is total- as Earth rotates, this small area will move
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Annular Solar Eclipse
The distance between the Moon and the Earth changes slightly during the Moon’s orbit
When the Moon is farthest from the Earth (apogee), then the solar eclipse will be annular the Moon does not
completely cover up the Sun
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Locations of Solar Eclipses for 1997-2020
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Total Solar Eclipse 2001Zambia, Africa
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Misconception:Phases of the Moon are caused by the shadow of the Earth on the Moon
Truth: Phases of the Moon are caused by our changing view of the illuminated side of the Moon• ½ of the Moon is always illuminated by the Sun
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Phases of the Moon• caused by its orbital motion around the Earth• repeat every 29 ½ days
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You can tell the moon phase by- looking at its face- observing what time it rises/sets
Full Moon
Rises ~ sunsetSets ~ sunrise
First Quarter Moon
Rises ~ noon Sets ~ midnight
New Moon
Rises ~ sunriseSets ~ sunset
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Time from New Moon to New Moon
The moon revolves around Earth in 27.3 days, however, the period from one new moon to the next one is 29.5 days.
In the 27.3 days in which the moon orbits Earth, the Earth moves along its orbit around the sun.
The moon must go a little farther to be directly between Earth and the sun.
About 2.2 days are needed for the moon to travel this extra distance.
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Tides on Earth
Bulges in Earth’s oceans, called tidal bulges, form because the moon’s gravitational pull on Earth decreases with distance from the moon.
As a result, the ocean on Earth’s near side is pulled toward the moon with the greatest force.
The solid Earth experiences a lesser force.
Because Earth rotates, tides occur in a regular rhythm at any given point on Earth’s surface each day.
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Causes of Tides
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Action of the Moon
The depth of water over each point changes as the Earth rotates. This produces two high and two low waters per day.
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Action of the Moon
The depth of water over each point changes as the Earth rotates. This produces two high and two low waters per day.
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Action of the Moon
The depth of water over each point changes as the Earth rotates. This produces two high and two low waters per day.
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Action of the Moon
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Action of the Moon
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Action of the Moon
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Action of the Moon
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Action of the Moon
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Action of the Moon
The depth of water over each point changes as the Earth rotates. This produces two high and two low waters per day.
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Check Your Knowledge Questions
1. If you observe the moon to be rising at sunset, what phase is it?
1. Full2. First Quarter3. New4. Third Quarter
2. If you observe the moon to be rising around midnight, what phase is it?
1. Full2. First Quarter3. New4. Third Quarter
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Asteroids, Comets, and Meteoroids
Chapter 28
Section 4
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Asteroids
In addition to the planets and their moons, our solar system includes millions of smaller bodies, such as asteroids, comets, and meteoroids.
The largest of these smaller bodies are asteroids, which are fragments of rock that orbit the sun.
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Asteroids
Astronomers have found over 50,000 asteroids. Millions asteroids may exist in the solar system.
The orbits of asteroids are ellipses.
Most asteroids are located in a region between the orbits of Mars and Jupiter known as the asteroid belt.
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Asteroids
Not all asteroids are located in the asteroid belt. The closest asteroids to the sun are inside the orbit of Mars.
The Trojan asteroids are concentrated in groups just ahead of and just behind Jupiter as it orbits the sun.
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Asteroid Belt
Apollo
Trojans
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Composition of Asteroids
The composition of asteroids is similar to that of the inner planets.
Asteroids are classified according to their composition into three main categories.
The first type of asteroid is also the most common; these asteroids are made mostly of silicate material.
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Composition of Asteroids
The second type of asteroid is composed of mostly iron and nickel. These asteroids have a shiny, metallic appearance, especially on fresh surfaces.
The third, and rarest, type of asteroid is made mostly of carbon materials, which give this type of asteroid a dark color.
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Near-Earth Asteroids
More than a thousand asteroids are called near-Earth asteroids because their orbits bring them close to Earth.
Several asteroid detection programs have begun to track all near-Earth asteroids.
By monitoring these asteroids, scientists hope to predict and possibly avoid future collisions.
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Ida - Dactyl
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Gaspra
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Asteroids Elsewhere
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Comets
The most famous comet is Halley’s Comet, which passes by Earth every 76 years.
It last passed Earth in 1986, and will return in 2061.
Every 5 to 10 years, a bright comet is visible from Earth.
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Composition of Comets
A comet has several parts. The core, or nucleus of a comet is made of rock, metals, and ice.
A spherical cloud of gas and dust, called the coma, surrounds the nucleus. The coma can extend as far as 1 million kilometers from the nucleus.
The nucleus and the coma form the head of the comet.
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Composition of Comets
The most spectacular part of a comet is its tail.
Tails form when sunlight causes the comet’s ice to change to gas. The solar wind pushes the gas away from the comet’s head.
The comet’s second tail is made of dust and curves backward along the comet’s orbit
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Structure of a Comet
To Sun
Ion Tail
Dust Tail
Coma
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Comet Structure
Nucleus10 km “Dirty Snowball”
ComaCloud of evaporated ices and ionsmay be 1,000,000 km in diameter
TailAlways points away from Sun
Solar Wind and Radiation Pressure
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The Oort Cloud
Scientists think that most comets originate in the Oort cloud.
The Oort cloud surrounds the solar system and may reach as far as halfway to the nearest star.
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The Oort Cloud
In 1950 Jan Oort noticed that no comet has been observed with an
orbit that indicates that it came from interstellar space,
there is no preferential direction from which comets come.
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The Oort Cloud
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The Oort Cloud
Bodies within the Oort cloud circle the sun so slowly that they take a few million years to complete one orbit.
But, the gravity of a star that passes near the solar system may cause a comet to fall into a more elliptical orbit around the sun.
If a comet takes more than 200 years to complete one orbit of the sun, the comet is called a long-period comet.
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The Kuiper Belt
Advances in technology have allowed scientists to observe many small objects beyond the orbit of Neptune.
Most of these objects are from the Kuiper belt and are called Kuiper-belt objects.
Pluto is located in the Kuiper belt during much of its orbit.
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Short-Period Comets
Comets called short-period comets take less than 200 years to complete one orbit around the sun.
Astronomers have discovered that most short-period comets come from the Kuiper belt.
Halley’s comet, which has a period of 76 years, is a short-period comet.
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Comet Halley
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Bayeaux TapestryNorman Invasion of 1066
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Comet Halley 1910
•Pope Callixtus III excommunicated Halley's Comet in 1456
•In 1910, charlatans sold "comet pills"
Orbit
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Comet of 1577
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Hyakutake
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Hale-Bopp
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Meteoroids
Most meteoroids have a diameter of less than 1 mm. Scientists think that most meteoroids have a diameter of less than 1 mm.
Scientists think that most meteoroids are piece of matter that become detached from passing comets.
Large meteoroids, which are more than 1 cm in diameter, are probably the result of collisions between asteroids.
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Meteoroids
When a meteoroid enters Earth’s atmosphere, friction heats and burn them up.
As the meteoroid burns up, it produces a bright streak of light called a meteor.
Meteors are often called shooting stars.
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The 1833 storm
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The 1966 storm
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1997 Leonids from Orbit
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What causes meteor showers?
1. Lots of falling stars
2. Clouds
3. Debris left in the path of a comet
4. Solar wind particles
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The Cause of Meteor Showers
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Two Showers for Halley
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Spot Question
What is the difference between a meteor and a meteoroid?
A meteoroid is a rocky body that travels through space. When a meteoroid enters Earth’s atmosphere and begins to burn up, the meteoroid becomes a meteor. Location, Location, Location!!!!!!
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Meteorites
Meteoroids that do not burn up, but fall to Earth’s surface, are called meteorites.
Most meteorites are small and don’t cause much damage, but occasionally large meteorites strike Earth’s surface with the force of a large bomb.
There are three types of meteorites: stony, iron, and stony-iron.
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Meteorites
Stony meteorites are similar in composition to rock on Earth.
Iron meteorites have a distinctive metallic appearance.
Stony-iron meteorites contain both iron and stone. Stony-iron meteorites are rare.
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Sporadic Meteors
Irons Stony-Irons
Chondrites Carbonaceous Chondrite
Achondrite
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Meteorites
Astronomers think that almost all meteorites come from collisions between asteroids.
The oldest meteoroids may be 100 million years older than Earth.
Meteorites may provide information about how the early solar system formed.
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Barringer’s Crater
An iron meteorite 100 feet across and 70,000 tons slamed into the Earth at about 43,000mph in the Arizona desert near Flagstaff 40,000 years ago. Barringer Crater is 4,100 feet wide and 571 feet deep.
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Other Impact Craters
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Tunguska, Siberia
June 30, 1908- Space object hit a sparsely populated and heavily forested area.
Explosion heard over a radius of 500 miles, covering an area of 500,000 square miles
Pressure wave was recorded passing England 5 hours and 15 minutes after impact
Blast equivalent to a 20-megaton H-bomb
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Tunguska, 1908
Nearly 1000 square miles of forest was flattened due to an air burst (meteor exploded before hitting the ground)
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K-T Boundary
In 1980, Walter Alvarez and a team of scientist discovered a thin layer of clay in Italy that contained Iridium and dated back 64,980,000 years ago.
Iridium is not naturally occurring on Earth, but is found in space.
The Alvarez Team named this layer of clay the K-T Boundary
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K-T Boundary
The K-T Boundary is evidence that a asteroid hit Earth and causes a ELE (Extension Level Event) eliminating 70% of life including the dinosaurs.
The boundary marks different time periods of dinosaurs and mammals. End of Cretaceous Period and Beginning of Tertiary Period.
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Chicxulub Crater
The problem the Alvarex team had with this hypothesis was there was no impact site.
In 1990,a crater 110 miles across in the Yucatan Peninsula (off the coast of Mexico) was identified as the impact site. The crater was named Chicxulub “The Devils Tail” and was caused by an asteroid approximately 6 miles long.
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Chicxulub Evidence
Besides the impact crater and iridium scientist have also found impact droplet and shocked quartz (crystalline structure of quartz is deformed) to support their theory.
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Walter Alvarez and Son at the K-T Boundary in Italy
K-T Boundary. Colorado
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What else can impacts cause?
1. Tsunami 2. Molten Rock 3. Debris Throw-up causing impact winters
and difficulty berating 4. Fire 5. Land shock
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Odds
Small chunks of matter hit and orbit Earth everyday. These object are called NEO’s – Near Earth Objects.
Only a small number of scientists jobs are to watch the sky for NEO’s
1/1Million odds of being killed by an ELE asteroid
1/100 Million odds of being killed by a small impact
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How Much Damage?
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Why is the study of comets, asteroids, and meteors important?
1. Predicting the future
2. Original solar nebula material
3. Useful in refining mass of solar system
4. It will be on the test
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And God said, “fire not flood next time.”
- Lyrics from Well, Well, Well by the group Peter, Paul, and Mary
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