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Interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes:

Interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes: Main Belt asteroid Hilda and Thule asteroid near-Earth asteroid (NEA) Trojan asteroid origin: rocky material that never accreted into a larger object; survivors of the planetary sweep-up process.

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Interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes:

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  1. Interplanetary bodies: asteroids asteroid-- rocky object in orbit around the sun includes: Main Belt asteroid Hilda and Thule asteroid near-Earth asteroid (NEA) Trojan asteroid origin: rocky material that never accreted into a larger object; survivors of the planetary sweep-up process

  2. Asteroid orbits object approx. a (AU) approx. e Main Belt 2.2 - 3.2 0 - 0.4 asteroid Hilda, Thule 3.9, 4.3 0 - 0.2 asteroid Trojan 5.2 (= Jupiter) 0 - 0.2 NEA 0.7 - 3 0.2 - 0.8 NEAs derived from Main Belt by perturbations

  3. Asteroid locations

  4. 2.2 AU Main Selected NEA orbits 3.2 AU

  5. Asteroid semi-major axes Hungaria- group Hilda- group Main Belt Trojans Thule- group

  6. Kirkwood gaps

  7. Kirkwood gaps • represent areas in asteroid belt relatively • free of material • form at locations (resonances) that experience • repeated perturbations from Jupiter • strong resonance locations include 1:3 & 2:5 • material in gaps moved elsewhere, such as into • planet-crossing orbits (e.g., NEAs)

  8. Asteroids: spectra & albedos

  9. Examples of asteroid spectral types

  10. Asteroid spectral types albedo main type (%) location (a) mineralogy analogue S 10-22 1.8-3.5 AU pyroxene O-chondrites? + - metal achondrites? + - olivine stony irons? M 10-20 2.3-3.2 AU metal iron meteorites C 3-7 2-4 AU hydrated C-chondrites silicates many meteors? + carbon comets? D + 2-6 3-5 AU carbon / none? P organic-rich comets? silicates

  11. Asteroids: different types in different locations

  12. Asteroids: examples Gaspra Ida Mathilde Vesta Eros

  13. Main Belt, S-type

  14. Main Belt, S-type member of family

  15. Main Belt, C-type

  16. Many large craters !

  17. NEA, possible chondrite parent body

  18. Eros: up close & personal The ultimate “meteorite” collecting site!

  19. Relative crater size- frequency diagram (“R plot”) Gaspra-- younger (recent collision?) Mathilde-- surplus of larger craters (how?)

  20. Asteroids: Eros geology

  21. Eros: the Saddle (Himeros)

  22. Eros: grooves & troughs

  23. Eros: ridges & grooves

  24. Eros: mass wasting

  25. Eros: ponds-- asteroidal sedimentary deposit

  26. Asteroids: Landing the NEAR spacecraft on Eros (or how to make an asteroid landing, without designing for it)

  27. Asteroids: Space weathering

  28. Space weathering-- • We have clear evidence for the importance • of space weathering on all asteroids seen up close. • On such asteroids, space weathering makes • objects redder, darker, and less crystalline.

  29. Color-exagerrated image

  30. Eros spectral reflectance: mineralogy 0.9 -1 micron band: Fe-bearing olivine, pyroxene 2 micron band: Fe-bearing pyroxene

  31. Eros: pyroxene signature Himeros Himeros Psyche

  32. Space weathering-- • A common process on asteroids • Color variations on Gaspra & Ida: “redder” color = more weathered • Albedo variations on Eros: darker = more weathered • Spectral variations on Eros: weaker pyroxene signature = more weathered

  33. Space weathering-- • Has important implications for making • links between asteroids and meteorites. • Probably involved in “pond” formation on • Eros. • Implies we can make sedimentary deposits on • asteroids or small-gravity objects by • space weathering. (Not seen on Moon.)

  34. Asteroids: NEAs

  35. NEAs: the more we look, the more we find them

  36. NEA asteroid 1999 JM8 diameter ~ 3.5 km a = 2.71 AU e = 0.65 i = 13.8o q = 0.96 AU radar images

  37. NEA asteroid 4179 Toutatis: “contact binary” or elongated asteroid? radar images diameter = 4.6 x 2.4 x 1.9 km a = 2.51 AU e = 0.63 i = 0.5o q = 0.92 AU

  38. NEA asteroid 1999 KW4: binary asteroid diameter of primary object ~ 1.2 km diameter of secondary object ~0.4 km orbital period ~ 16 hrs a = 0.64 AU e = 0.69 i = 39o q = 0.20 AU radar images

  39. Target: Earth? NEA asteroid 1950 D4 diameter ~1.1 km rot. period ~2.1 hrs a = 1.70 AU e = 0.51 i = 12.2o q = 0.84 AU

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