Chapter 3: Near-Earth Objects 1.Chevy Asteroid (not Chevy Astro)Chevy Asteroid (not Chevy Astro)...

Chapter 3: Near-Earth Objects

1. Chevy Asteroid (not Chevy Astro)

2. Characteristics of Near-Earth Objects

3. Impact Features

4. Impact Hazards

5. Beware of Flying Rocks

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Chevy Asteroid (not Chevy Astro)

The Good Earth, Chapter 3: Near-Earth Objects

1992: A football-sized meteorite crashed through the trunk of Michelle Knapp’s Chevrolet Malibu Classic in Peekskill, New York

Near-Earth objects (NEOs) are asteroids or comets that approach Earth

What are the chances that a larger space object will crash into Earth in the near future?

Chevy Asteroid (not Chevy Astro)

Barringer (Meteor) Crater, Arizona formed approximately 50,000 years ago when a 50-meter diameter meteorite crashed to Earth.

Earth carries the scars of past impacts with asteroids and comets

A devastating collision with a 10-km wide asteroid is hypothesized to have caused a global extinction event 66 million years ago


Go back to the Table of Contents

Go to the next section: Characteristics of Near-Earth Objects


Characteristics of Near-Earth Objects


In 2029, the asteroid Apophis is expected to come within 36,000 km of Earth . . . about here.

Most NEOs do not come close to Earth but occasionally one may approach within the moon’s orbit



Few asteroids were recognized in the inner solar system 100 years ago.

Today, more than 90,000 asteroids have been identified. (Red squares = NEOs)



Asteroids

• Size – space pebbles to 940 km in diameter (Ceres)

• Travel at ~16 km/s (36,000 mph)

• Composed of rock and/or metals− Meteor – asteroids that

burn in atmosphere

− Meteorite – an asteroid that strikes Earth’s surface

Asteroid 433 Eros

Near-Earth Objects Conceptest

What characteristics are true for both planets and asteroids

A. They are approximately spherical in shape.

B. There are thousands of examples.

C. They formed 1 to 2 billion years ago.

D. They are present in the solar system.


Near-Earth Objects Concept Survey

1. Radius greater than 500 km2. Essentially spherical in shape3. Orbit the Sun4. Have a gravitational field5. Can rotate6. May be made of materials

similar to Earth7. Possess moons8. Thousands of examples9. Most have atmospheres10. Have less predictable orbits11. Have a variety of shapes12. Formed after the Big Bang 4

billion years ago. 13. Have craters14. Some will collide with Earth15. Example: Pluto16. Example: Eros

Planets Asteroids

Venn Diagram: Planets vs. AsteroidsPlace the numbered items in the appropriate fields in the Venn Diagram.

4

7

10



Comets

• Size – generally larger than asteroids − Many are 100s km across

• Travel faster than asteroids − ~50 km/s (112,000 mph)

• Composed of dust and ice with a rocky core

− “icy dirtballs”

Comet “tail” forms as heat from sun causes ice to change from solid to a gas. The “tail” points away from the sun



Comets

• Analysis of light from explosion on Tempel 1 revealed information on comet composition

• Common compounds present including− Cyanide

− Carbon dioxide

− Water – scientists are investigating if comets could have supplied water in Earth’s early oceans

Collision of “impactor” spacecraft with comet Temple 1, July 4, 2005



Comets

• 1908 Explosion of a comet in the atmosphere over Tunguska, Russia, destroyed forest over an area the size of a major city (2,100 km2)

Trees knocked down by a comet exploding in the atmosphere over Tunguska



Two types of comets

• Short-period comets − originate in Kuiper Belt

beyond Neptune

− Return to inner solar system every few years

• Long-period comets − Originate in the Oort

Cloud at the outer limits of the heliosphere

− Return orbits over decades to thousands of years

Oort Cloud

Kuiper Belt



• Long-period comets − Travel toward the sun with

irregular orbits that may be at a high angle to planets

• Short-period comets − Orbit sun with similar

paths to outer planets



Where is the Kuiper Belt relative to the asteroid belt?

A. The Kuiper Belt is closer to the sun than the Asteroid Belt.

B. The Kuiper Belt is farther from the sun than the Asteroid Belt.

C. The Kuiper Belt and Asteroid Belt are located in the same region of the solar system.



1. Diameter greater than 1,000 km

2. Orbit the sun

3.

4.

5.

6.

7.

8.

9.

10.

11.

12.

Planets Comets

Venn Diagram: Planets vs. CometsComplete the Venn diagram by adding more characteristics to the partial list and place the numbers in the corresponding locations on the diagram.

2

1



Go to the next section: Impact Features


Impact Features

• NEO collisions with rocky planets and moons formed 2 types of impact craters − Simple craters

− Complex craters

Barringer (Meteor) Crater, Arizona, a simple crater formed 50,000 years ago. This was the

first meteorite crater recognized on Earth.

1,200 meters


Impact Features

• Craters all feature− Broken rocks (breccia)

− Ejecta thrown from crater

− Melt rocks

− Altered minerals

• Simple Craters − Bowl-shaped

− Few kilometers wide

• Complex Craters− More than 4 km diameter

− Central peak, ring structures


Impact Features

Ejecta blanket surrounding the crater

Bowl-shaped

2,600 meters

Simple crater• Unnamed

crater on Mars


Impact Features

Ejecta blanket surrounding crater • Eratosthenes crater

on the moon• 58 km diameter

Complex crater

Ring-structures around edge of crater

Small simple craters

Central peak


Impact Features

• Crater vs. NEO size − An impact crater is 10-20

times larger than the colliding NEO

− Example: Manicouagan Crater, Canada

~100 km wide crater

NEO was 5-10 km in diameter

Remains of the 200 million year-old Manicouagan Crater, Canada.


Impact Features

• Craters on Earth

− More than 150 impact craters identified on continents

− Few impact sites identified in oceans

Why?

Sites of the 10 largest impact craters on Earth.



Meteor crater (1,200 meters wide) was formed by an NEO about the size of a

A. Car

B. Two-story house

C. 15-floor office building

D. City block



Which diagram best illustrates the land profile across a complex crater?



Go to the next section: Impact Hazards


Impact Hazards

• The impact of an NEO with a diameter equivalent to − the Lincoln Memorial (~50

meters) would destroy a large city

− the National Mall (~1 km) collides with Earth every 100,000 years and would devastate most nations

− Washington, D.C., (~10 km) collides with Earth every 100 million years and would produce global-scale destruction

Key buildings of Washington, D.C.


Impact Hazards

• Large NEO impacts are infrequent − Impacts of relatively

small NEOs (~50 meters) occur at intervals of hundreds to thousands of years

− Large NEO (10+ km) impacts occur on time scales measured in hundreds of millions of years


Impact HazardsWhat would happen if a 10 km NEO collided with Earth?


Impact HazardsWhat would happen if a 10 km NEO collided with Earth?

1. Fireball racing through atmosphere

2. People at impact site, seconds to live

3. Air blast would flatten everything for hundreds of kilometers in all directions

4. Massive earthquake at collision

5. Ocean impact would produce giant tsunami hundreds of meters high

6. Molten rock from collision would rain down, start massive wildfires

7. Huge cloud of dust blocks sunlight, cools planet for months, kills off most vegetation

8. Gases from impact – sulfur dioxide, water vapor – added to atmosphere The Good Earth, Chapter 3: Near-Earth Objects


Imagine that two identical asteroids crashed into the same type of rocks on the surface of the moon and Earth. Both produce impact craters. How do the impact craters compare?

A. The crater on the moon will be larger

B. The crater on Earth will be larger

C. The craters will have the same dimensions



Two 1-km-wide asteroids collide with Earth. The first asteroid strikes a desert area 1,000 km from the city of Bang, with a population of 1 million people. The other lands in the open ocean 1,000 km from an identical city named Crash that also has 1 million people. Both cities are located along low-lying coasts similar to the Atlantic coast of the eastern US.

Predict which city will experience the most damage.

Explain your choice.



Go to the next section: Beware Flying Rocks


Beware Flying Rocks

• NEO impacts are the only major natural hazards that we have the potential to prevent − Can’t stop volcanic eruptions

− Can’t stop earthquakes

− Can’t stop hurricanes

• With fore-warning, NEOs could potentially be deflected off-course or destroyed• Scientists have already hit a comet with a

spacecraft and landed a spacecraft on an asteroid


Beware Flying Rocks

NEO Detection• Current NEO search programs focus on the

approximately 1,000 objects with diameter of more than 1 km− Search programs are looking for fast-moving dark

objects against the backdrop of space

− Largest NEOs pose the greatest risk and are easiest to find

− Scientists map position of specific NEOs over time to chart their course relative to Earth


Beware Flying Rocks

• The Torino Scale − 0 = NEO will miss Earth or

burn up in atmosphere.

− 1 (green) = will pass near Earth but extremely unlikely to impact.

− 2-4 (yellow) = NEO with minor chance of impact.

− 5-7 (orange) = serious threat of impact, planning may be warranted.

− 8-10 (red) = certain collision, number corresponds to size of NEO.


Use information from this chapter to identify interactions between NEOs and

the earth system.


The End



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