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Asteroids and Meteorites

Asteroids and Meteorites. Asteroid Facts. Asteroids are rocky leftovers of planet formation . Asteroids are cratered and not round. The largest is Ceres, diameter ~1000 kilometers. 150,000 in catalogs, and probably over a million with diameter >1 kilometer.

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Asteroids and Meteorites

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  1. Asteroids and Meteorites

  2. Asteroid Facts • Asteroids are rocky leftovers of planet formation. • Asteroids are cratered and not round. • The largest is Ceres, diameter ~1000 kilometers. • 150,000 in catalogs, and probably over a million with diameter >1 kilometer. • Small asteroids are more common than large asteroids. • All the asteroids in the solar system wouldn’t add up to even a small terrestrial planet.

  3. Asteroids with Moons • Some large asteroids have their own moon. • Asteroid Ida has a tiny moon named Dactyl.

  4. Asteroid Orbits • Most asteroids orbit in the asteroid belt between Mars and Jupiter. • Trojan asteroids follow Jupiter’s orbit. • Orbits of near-Earth asteroids cross Earth’s orbit.

  5. Origin of Asteroid Belt • Rocky planetesimals between Mars and Jupiter did not accrete into a planet. • Jupiter’s gravity, through influence of orbital resonances, stirred up asteroid orbits and prevented their accretion into a planet.

  6. If you discover an asteroid and track its orbit, you get to name it.

  7. Meteorites

  8. Meteor Terminology • Meteorite: a rock from space that falls through Earth’s atmosphere • Meteor: the bright trail left by a meteorite • Falling star = meteor • Bolide = a really bright meteor

  9. Near Earth Asteroids

  10. Meteorite Impact Chicago, March 26, 2003

  11. Meteorite Types • Primitive: unchanged in composition since they first formed 4.6 billion years ago • Processed: younger; have experienced processes like volcanism or differentiation • Stony Meteorites; Iron Meteorites

  12. Stony Meteorite

  13. Iron Meteorite

  14. Meteorites from Moon and Mars • A few meteorites arrive from the Moon and Mars. • Composition differs from the asteroid fragments. • A cheap (but slow) way to acquire Moon rocks and Mars rocks

  15. Meteor Showers • Many meteors seeming to come in along radiants

  16. Meteors in a meteor shower appear to emanate from the same area of sky because of Earth’s motion through space.

  17. Tektites Glassy fragments, Probably formed by impacts

  18. Impacts and Mass Extinctions

  19. K-T Boundary • K-T Boundary (Cretaceous-Tertiary) • There is an excess of iridium everywhere on the Earth at the layer • which was laid down 65 million years ago. • Iridium is rare on Earth, but is common in certain types of meteorites. • 65 million years ago, there was a mass extinction, 75-80% of all species • died suddenly, including the dinosaurs, pterosaurs, ammonites and • most marine reptiles • A large impact killed the dinosaurs

  20. Other Mass Extinctions At least 5 other mass extinctions in the fossil record Largest was at the end of the Permian Period, 245 million years ago, when over 96% of the species alive at the time became extinct. There is no evidence for a meteor impact causing any of the other mass extinctions

  21. Should we worry? Estimate that the odds that you will die from an impact of an asteroid in any given year is about 1 in 20,000

  22. Gary Larson probably got it right

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