Asteroids, Comets and Meteorites

1. Asteroids, Comets and Meteorites

2. Important Points • Small objects in the solar system are leftovers that never accreted into planets • Minor planets mostly orbit between Mars and Jupiter • Comets formed in the outer solar system and were flung outward by close encounters with other planets • Comets can be trapped in the inner solar system by planetary encounters • The head and tail of a comet glow from sunlight shining on gases evaporated from the comet • Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets • Occasionally comets or minor planets collide with larger objects like the earth

3. Small Bodies of the Solar System • Asteroids: within the orbit of Jupiter • Centaurs: Between Jupiter and Neptune • Kuiper Belt Objects (KBO’s): Beyond Neptune • Scattered Disk: Extreme KBO’s • Comets: Icy bodies with elongated orbits • Meteoroids: Small objects • Meteors: vaporize in Earth’s atmosphere • Meteorites: survive to reach surface 1. Small objects in the solar system are leftovers that never accreted into planets

4. The Bode-Titius Law • The planets have fairly regular spacings • Start with 0, 3, 6, 12, 24, 48, 96, 192, 384, 788 • Add 4: 4, 7, 10, 16, 28, 52, 100, 196, 388, 792 • Divide by 10: 0.4, 0.7, 1.0, 1.6, 2.8, 5.2, 10 … • Matches distances of planets in A.U. • What’s at 2.8? • First Asteroid Discovered, 1801 2. Minor planets mostly orbit between Mars and Jupiter

5. The Bode-Titius Law • Neptune,discovered in 1846, matched the predicted 38.8 value poorly (30.1) • Pluto didn’t match at all (39.5 versus 79.2) • Coincidence? • Or is the Bode-Titius pattern due to the influence of Jupiter and planetary clearing? 2. Minor planets mostly orbit between Mars and Jupiter

6. Other Hypothetical Planets • Vulcan • Hypothetical planet within the orbit of Mercury • Some asteroids and many comets cross the orbit of Mercury, but nothing is known to orbit entirely within the orbit of Mercury • Planet X • Hypothetical massive outer planet beyond Neptune • Nemesis • Hypothetical dwarf star companion to Sun

7. The Asteroid Belt, 2001

8. The Asteroid Belt, 2010

9. Asteroid Discoveries 2. Minor planets mostly orbit between Mars and Jupiter

10. 2010 SEPT. 2 • 535789 Minor planets catalogued • 251651 Officially numbered • 16154 Named 2. Minor planets mostly orbit between Mars and Jupiter

11. How We Study Them • Spacecraft • Ground-Based and Hubble Imaging • Radar Imaging 2. Minor planets mostly orbit between Mars and Jupiter

12. Spacecraft Images 2. Minor planets mostly orbit between Mars and Jupiter

13. 951 Gaspra (15 km)

14. 243 Ida (40 km) and Dactyl

15. 253 Mathilde (50 km)

16. Three Asteroids Compared

17. 433 Eros (20 km)

18. Eros

19. Eros 2. Minor planets mostly orbit between Mars and Jupiter

20. Asteroid Itokawa 2. Minor planets mostly orbit between Mars and Jupiter

21. Spacecraft Shadow

23. Earth-Based Optical Imaging 2. Minor planets mostly orbit between Mars and Jupiter

24. 4 Vesta (500 km)

25. Ceres and Vesta

26. Radar Imaging 2. Minor planets mostly orbit between Mars and Jupiter

27. Double Asteroids

28. Comets 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets

29. Types of Comets • Short Period (<200 years) • Record reobserved comet is Comet Ikeya-Zhang (1661-2002) • Long Period (>200 years) • Hale-Bopp (2400 years) • Need a source very far away • Oort Cloud • Too little material very far from the Sun • Flung out by planetary encounters 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets

30. Where Comets Come From • Ice and Frozen Gases • Outer Solar System (Kuiper Belt) • Planetary Encounters perturb Orbits • Diverted inward to become short-period • Diverted outward to Oort Cloud 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets

31. Creation of Long Period Comet 3. Comets formed in the outer solar system and were flung outward by close encounters with other planets

32. Capture of Short Period Comet 4. Comets can be trapped in the inner solar system by planetary encounters

33. Anatomy of a Comet

34. Comet McNaught 2008

35. Comet McNaught 2008

36. Record-Breaking Hale-Bopp • Most-observed comet in history • Discovered the furthest from the Sun • Largest cometary nucleus known • Visible to the naked eye for 18 months – twice the previous record • Brighter than magnitude 0 for eight weeks, longer than any other comet in the last thousand years. 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet

37. Comet Hale-Bopp 1997 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet

38. Halley’s Comet 5. The head and tail of a comet glow from sunlight shining on gases evaporated from the comet

39. Comet Holmes 2007

40. Comet Borelly

41. Comet Tempel I

42. The Deep Impact Mission

43. A Comet Hits The Sun

44. Meteoroids • Meteoroid – Small object orbiting Sun • Meteor – Meteoroid that becomes incandescent from friction with atmosphere • Bolide or Fireball – Exceptionally brilliant meteor • In impact studies, “bolide” often used for an impacting meteoroid prior to impact • Meteorite – A meteoroid that reaches the surface • Micrometeorite – microscopic meteoroid 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets

45. Bolide

46. Meteor Showers • Earth passes through streams of orbiting debris • Many linked to orbits of known comets • Occur predictably • Perseids: August • Orionids: October (Halley’s Comet) • Leonids, November • No known falls • Generally 20 or so per hour, rarely 1000’s • Appear to radiate from one point in sky 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets

47. A Meteor Shower

48. Radiant

49. Meteorites • Stony (95%) • Chondrites: Pellet-like texture • Carbonaceous Chondrites: Most similar to the Sun (minus gases), planetary raw material • Achondrites: Basalt • Stony-Iron (1%) • Nickel-Iron (4%) • Kamacite (>6% Ni) and Taenite (>25% Ni) • Texture revealed by etching 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets

50. Finding Meteorites • Finds versus Falls • Fall: Observed to fall, then recovered • Find: Identified long after fall • Stony Meteorites weather and are hard to tell from natural rocks • Iron meteorites are more easily recognized • Prime Scientific Collecting Localities • Antarctica • Deserts 6. Meteors and meteorites are pieces broken off larger bodies by collisions, or dust shed by comets