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Comets Asteroids and Meteorites Ch 9

Comets Asteroids and Meteorites Ch 9. Ch 8 and 9 HW posted and due Mon March. 14. COMETS AND THEIR COMPOSITION (Ch. 9 part II). OUTLINE. I. Nature of Comets II. Comets and the Origin of Earth’s Water III. Dust Composition Summary ( you need to take notes only on slides with blue titles).

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Comets Asteroids and Meteorites Ch 9

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  1. Comets Asteroids and MeteoritesCh 9 Ch 8 and 9 HW posted and due Mon March. 14

  2. COMETS AND THEIR COMPOSITION(Ch. 9 part II)

  3. OUTLINE I. Nature of Comets II. Comets and the Origin of Earth’s Water III. Dust Composition • Summary (you need to take notes only on slides with bluetitles)

  4. Comet Hale-Bopp in 1997

  5. I. Nature of Comets Comets from the Greek “” (kometes). Long-haired ones. Ancient greeks considered comets atmospheric phenomena, not part of the “perfect” heavens.

  6. Question 1 A comet is: A piece of interplanetary material that burns in the Earth’s atmosphere An object made of ices and dust in orbit around the Sun A shooting Star A rocky object that formed between Mars and Jupiter

  7. I. Nature of Comets Today we know comets are “dirty icebergs” in orbit around our Sun. About ½ of a comet’s mass is water ice, the rest is cosmic dust and other ices. Comet Orbits:generally very elliptical

  8. I. Nature of Comets (Cont.) The nucleus is where all cometary activity originates. When a comet is far from the Sun it is an inert object. When a comet approaches the Sun the ices in the nucleus sublimate and create a cloud of gas and dust called the coma. Sunlight and the solar wind push the dust and gas away from the sun creating the two tails.

  9. Question 2 The tails of comets are always directly behind the nucleus. a) True b) False

  10. Comet Hale-Bopp (Image byElizabeth Warner on March 8, 1997) Ion Tail Dust Tail Coma

  11. Comet Ikeya-Zhang(March 11 ‘02 images from Sky and Telescope)

  12. DS1 Spacecraft Image of Comet Borrelly in September 2001

  13. Image of Comet Wild 2 from NASA's Stardust spacecraft. January 2, 2004

  14. Deep Impact Spacecraft Image of Comet Tempel 1 in July 2005

  15. Deep Impact Spacecraft Image of Comet Tempel 1 in July 2005

  16. I. Nature of Comets(Cont.) Our solar system formed about 4.6 billion years ago from the solar nebula. The planets and Sun have been extensively processed since they formed. However, comets have remained relatively pristine for the past 4.6 billion years. Why? Comets are small and stay far from the Sun most of the time.

  17. Nature of Comets (Cont.) • Two Known Sources of Comets • Oort Cloud (spherical shell ~ 50,000-100,000 AU) • Kuiper Belt (disk ~ 30-50 AU) (Astronomical Unit [AU] = Earth-Sun Distance) • Active comets do not last more than about 100,000 years in the inner solar system because they lose material every time they pass near the Sun

  18. Oort Cloud Sun ~105 AU About 1/3 distance to nearest star

  19. ~50 AU Sun Kuiper Belt Neptune’s Orbit

  20. Comets can come from the Oort Cloud and from the Kuiper belt Jovian planets protect Earth from most of bombardment Fig 9.25

  21. Outer Solar System

  22. Outer Solar System

  23. Collision in the Kuiper BeltPaiting by Daniel D. Durda

  24. Comet SL9 caused a string of violent impacts on Jupiter in 1994, reminding us that catastrophic collisions still happen. Tidal forces tore it apart during previous encounter with Jupiter

  25. COMPOSITION OF COMET GAS Deuterium Abundance: • Why study it? • Chemical signature that can help us understand the possible links between comet water and Earth’s water

  26. Deuterium Atom Hydrogen Atom P N P + + - - e e III. COMPOSITION (Cont.)

  27. Normal and “Heavy” Water H2O HDO O O H H H D

  28. COMPOSITION OF COMET GAS Deuterium Abundance: • The deuterium to hydrogen ratio has been measured in the water vapor in the coma of three comets: Halley, Hyakutake, and Hale-Bopp • These vales are plotted in the next slide

  29. 10-5 10-3 Deuterium/Hydrogen Ratios •HB •HA •HY Earth Oceans 10-4 Solar Nebula

  30. 10-5 10-3 D/H Ratios Cores of Molecular Clouds •HB •HA Comets •HY Earth Oceans C Chondrites (H2O-rich meteorites) 10-4 Solar Nebula

  31. III. COMPOSITION (Cont.) • D/H Ratios in Comet Water: • Consistent with comets providing at least some of Earth’s H2O

  32. IV. Comets and Origin of Earth’s Water The contents of H2O in meteorites indicates a decrese in water abundance in the asteroid belt with decreasing heliocentric distance Meteorites believed to have originated in the innermost part of the asteroid belt are the driest known material in the solar system This suggests that the planetesimals formed in Earth’s zone should have had an even lower water content

  33. Water contents of meteorites (which come from asteroids) Wet Dry

  34. IV. Comets and Origin of Earth’s Water Why is Earth rich in water and where did this water come from? Comet impacts? Asteroid impacts? Probably both: The composition Earth’s water is consistent with a cometary origin of at least some of it. In addition, some asteroids can have as much as 15% water

  35. V. COMPOSITION OF THE DUST • Cometary dust is approximately 50% silicates (minerals) and 50% organic solids (organic solids are made up of molecules with many carbon atoms). • If comets contributed a significant fraction of Earth’s H2O they probably also contributed significant quantities of organic molecules. • Hence, comets may have played a role in the origin of life on Earth. • However, there is no evidence that comets bring living organisms to Earth.

  36. VI.SUMMARY Comets are composed mainly of H2O ice plus cosmic dust and other ices The main features of a comet are the nucleus, coma and tails There are two known sources of comets: Oort Cloud and Kuiper Belt The chemical composition of comets (rich in deuterium) is consistent with a cometary origin of at least some of Earth’s water and organic molecules

  37. Asteroids and MeteoritesCh9 part III

  38. Asteroids and Meteorites Outline I. Introduction • Asteroids • Orbits, sizes, composition III. Meteorites • Irons • Stony-Irons • Stones IV. Origin of Meteorites V. Meteorites and the Solar System VI. Summary

  39. I. INTRODUCCION Asteroids, comets and meteorites are the smallest members of the solar system All these objects tell us much about how the rest of the solar sytem formed

  40. II. ASTEROIDS Most have orbits between between Mars and Jupiter Some have orbits that cross Earth’s, these are known as Earth-crossing asteroids They have collided with Earth and they are likely to do so again. The largest asteroid is Ceres

  41. III. Types of Meteorites Iron Irons Stony-Irons Stones (~75% of all meteorites) Iron and stone Stone Differenciated Asteroid Non-differenciated Asteroid

  42. III. Types of Meteorites Irons Stony-Irons Stones (~75% of all meteorites)

  43. Iron Meteorite

  44. Stony-Iron

  45. Stony Meteorite

  46. III. Origin of Meteorites • Asteroids (more than 95%) • Asteroids collide with each other and breakup, some of those fragments become meteorites • Mars (a few percent) • Impacts on Mars kick martian material into space and some ends up falling on Earth • Moon (a few percent) • Also because of impacts

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