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Chapter 3: Near-Earth Objects

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

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Chapter 3: Near-Earth Objects

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  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. 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.

  4. 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)

  5. 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  18. 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

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

  20. 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

  21. 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

  22. 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

  23. 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

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