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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 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 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 Volcanic Shock Wave http://www.wimp.com/volcanicmount/ 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. 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) 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 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 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 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 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