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)
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?
The Good Earth, Chapter 3: Near-Earth Objects
Chevy Asteroid (not Chevy Astro)
Earth carries the
scars of past impacts
with asteroids and
comets
Barringer (Meteor) Crater, Arizona formed
approximately 50,000 years ago when a 50-meter
diameter meteorite crashed to Earth.
A devastating
collision with a 10-km
wide asteroid is
hypothesized to have
caused a global
extinction event 66
million years ago
The Good Earth, Chapter 3: Near-Earth Objects
Go back to the Table of Contents
Go to the next section: Characteristics of
Near-Earth Objects
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Most NEOs do not come close to Earth
but occasionally one may approach
within the moon’s orbit
In 2029, the asteroid Apophis is
expected to come within 36,000
km of Earth . . . about here.
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Few asteroids were
recognized in the inner solar
system 100 years ago.
Today, more than 90,000
asteroids have been identified.
(Red squares = NEOs)
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
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
Asteroid 433 Eros
− Meteorite – an asteroid
that strikes Earth’s
surface
The Good Earth, Chapter 3: Near-Earth Objects
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.
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Concept Survey
Venn Diagram: Planets vs. Asteroids
Place the numbered items in the
appropriate fields in the Venn Diagram.
Planets
Asteroids
4
7
10
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
Radius greater than 500 km
Essentially spherical in shape
Orbit the Sun
Have a gravitational field
Can rotate
May be made of materials
similar to Earth
Possess moons
Thousands of examples
Most have atmospheres
Have less predictable orbits
Have a variety of shapes
Formed after the Big Bang 4
billion years ago.
Have craters
Some will collide with Earth
Example: Pluto
Example: Eros
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Comets
• Size – generally larger
than asteroids
Comet “tail” forms as heat
from sun causes ice to change
from solid to a gas. The “tail”
points away from the sun
− 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”
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Comets
• Analysis of light from
explosion on Tempel 1
revealed information on
comet composition
• Common compounds
present including
− Cyanide
− Carbon dioxide
Collision of “impactor” spacecraft with
comet Temple 1, July 4, 2005
− Water – scientists are
investigating if comets
could have supplied water
in Earth’s early oceans
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
Two types of comets
• Short-period comets
− originate in Kuiper Belt
beyond Neptune
− Return to inner solar
system every few years
• Long-period comets
Kuiper Belt
Oort Cloud
− Originate in the Oort
Cloud at the outer limits of
the heliosphere
− Return orbits over
decades to thousands of
years
The Good Earth, Chapter 3: Near-Earth Objects
Characteristics of Near-Earth Objects
• 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
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Conceptest
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.
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Concept Survey
Venn Diagram: Planets vs. Comets
Complete the Venn diagram by adding
more characteristics to the partial list and
place the numbers in the corresponding
locations on the diagram.
Planets
Comets
1. Diameter greater than 1,000 km
2. Orbit the sun
3.
4.
5.
6.
2
7.
8.
1
9.
10.
11.
12.
The Good Earth, Chapter 3: Near-Earth Objects
Go back to the Table of Contents
Go to the next section: Impact Features
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
• NEO collisions with rocky
planets and moons formed
2 types of impact craters
− Simple craters
− Complex craters
1,200 meters
Barringer (Meteor) Crater, Arizona, a simple
crater formed 50,000 years ago. This was the
first meteorite crater recognized on Earth.
The Good Earth, Chapter 3: Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
Simple crater
• Unnamed
crater on Mars
Bowl-shaped
2,600 meters
Ejecta blanket
surrounding
the crater
The Good Earth, Chapter 3: Near-Earth Objects
Impact Features
Complex crater
Ejecta blanket
surrounding crater
• Eratosthenes crater
on the moon
• 58 km diameter
Central peak
Ring-structures
around edge of crater
Small simple craters
The Good Earth, Chapter 3: Near-Earth Objects
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.
The Good Earth, Chapter 3: Near-Earth Objects
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.
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Conceptest
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
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Conceptest
Which diagram best illustrates the land
profile across a complex crater?
The Good Earth, Chapter 3: Near-Earth Objects
Go back to the Table of Contents
Go to the next section: Impact Hazards
The Good Earth, Chapter 3: Near-Earth Objects
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
Key buildings of Washington, D.C.
− Washington, D.C., (~10 km)
collides with Earth every 100
million years and would
produce global-scale
destruction
The Good Earth, Chapter 3: Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
What would happen if a 10 km NEO collided with Earth?
The Good Earth, Chapter 3: Near-Earth Objects
Impact Hazards
What 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
Near-Earth Objects Conceptest
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
The Good Earth, Chapter 3: Near-Earth Objects
Near-Earth Objects Concept Survey
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.
The Good Earth, Chapter 3: Near-Earth Objects
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Go to the next section: Beware Flying Rocks
The Good Earth, Chapter 3: Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects
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.
The Good Earth, Chapter 3: Near-Earth Objects
Use information from this chapter to
identify interactions between NEOs and
the earth system.
The Good Earth, Chapter 3: Near-Earth Objects
The End
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The Good Earth, Chapter 3: Near-Earth Objects