1. Chapter 3: Near-Earth Objects
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

2. Chevy Asteroid (not Chevy Astro)
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
Barringer (Meteor) Crater, Arizona formed approximately 50,000 years ago when a 50-meter diameter meteorite crashed to Earth.

3. Russia Chelyabinsk 2/15/2013 http://www.wimp.com/meteorexplodes/
40,000-43,000 miles per hour
Exploded at 98,000 feet (18 miles) altitude
1,500 injured, 7,200 building damaged, 14,000 tons

4. Volcanic Shock Wave

5. 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.

6. 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)

7. 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
Meteorite – an asteroid that strikes Earth’s surface
Asteroid 433 Eros

8. Characteristics of Near-Earth Objects
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
The Good Earth, Chapter 3: Near-Earth Objects

9. 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
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
The Good Earth, Chapter 3: Near-Earth Objects

10. 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

11. 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
Originate in the Oort Cloud at the outer limits of the heliosphere
Return orbits over decades to thousands of years
Kuiper Belt
Oort Cloud
The Good Earth, Chapter 3: Near-Earth Objects

12. 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

13. 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

14. Impact Features Craters all feature Simple Craters Complex Craters
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

15. 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

16. 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

17. Remains of the 200 million year-old Manicouagan Crater, Canada.
Impact Features
Crater vs. NEO size
An impact crater is 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

18. Sites of the 10 largest impact craters on Earth.
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

19. Key buildings of Washington, D.C.
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.
The Good Earth, Chapter 3: Near-Earth Objects

20. 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

21. What would happen if a 10 km NEO collided with Earth?
Impact Hazards
What would happen if a 10 km NEO collided with Earth?
The Good Earth, Chapter 3: Near-Earth Objects

22. What would happen if a 10 km NEO collided with Earth?
Impact Hazards
What would happen if a 10 km NEO collided with Earth?
Fireball racing through atmosphere
People at impact site, seconds to live
Air blast would flatten everything for hundreds of kilometers in all directions
Massive earthquake at collision
Ocean impact would produce giant tsunami hundreds of meters high
Molten rock from collision would rain down, start massive wildfires
Huge cloud of dust blocks sunlight, cools planet for months, kills off most vegetation
Gases from impact – sulfur dioxide, water vapor – added to atmosphere
The Good Earth, Chapter 3: Near-Earth Objects

23. 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

24. 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

25. 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