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William Bottke Southwest Research Institute Boulder, Colorado

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William Bottke Southwest Research Institute Boulder, Colorado

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    1. In this talk I will show you that Southwest Research Institute? is at the forefront of understanding the solar wind that fills the space around our solar system and its interaction at the galactic frontier!In this talk I will show you that Southwest Research Institute? is at the forefront of understanding the solar wind that fills the space around our solar system and its interaction at the galactic frontier!

    2. Meteorites and Their Parent Bodies Fact: Nearly all meteorites come from the main belt. Irons, stony-irons, ordinary and carbonaceous chondrites, achondrites, etc.

    3. Part 1: The Standard Model

    4. “Classical” Main Belt Evolution

    5. Taxonomic Stratification in Early Main Belt

    6. Mixing of Taxonomic Types

    7. Part 2: Problem: Where Do Iron Meteorites Come From?

    8. Iron Meteorites Irons represent two-thirds of the unique parent bodies represented in our meteorite collection. They sample the cores of small differentiated asteroids (D < 200 km) and are ~1-2 My older than chondrules. Collisions of some form are needed to extract core material from their parent bodies. This should produce mantle (olivine) and crust (basaltic) fragments.

    9. We Infer From Meteorites That…

    10. Observations of Main Belt Asteroids (4) Vesta is the only known intact differentiated asteroid. Asteroid families show no obvious signs of silicate melting (i.e., no obvious core, mantle, crust). Few asteroids are fragments from differentiated bodies (some V-, A-, M-types).

    11. We Infer From Asteroids That…

    12. Questions & Answers How can we reconcile these differences? Meteorites: Small differentiated asteroids were once common. Asteroids: Little differentiation ever occurred in main belt.

    13. Differentiation in Terrestrial Planet Region 26Al produces heat but decays quickly (t1/2 = 0.73 My). Only fast-growing planetesimals have a chance to melt. Growth is a function of heliocentric distance and swarm density. Until we reach snowline, the fastest-growing planetesimals are close to Sun.

    14. Inner Solar System Planetesimals

    15. Fraction Reaching Main Belt Zone

    16. Fraction Reaching Main Belt Zone

    17. Part 3: Where Do Primitive Meteorites Come From? Where Did They Originate?

    18. Are Micrometeorites From Comets? Most unmelted MMs are similar to primitive chondrites (e.g., CI, Tagish Lake) Primitive meteorites came from asteroid belt. If they are from asteroids, why are so few MMs ordinary chondrites? If from comets, how did they arrive unmelted?

    19. Some Comet Material Looks Asteroidal STARDUST samples most closely resemble primitive chondritic meteorites from the asteroid belt.

    20. P and D-Type Asteroids Look Like Dormant Comets

    21. New Solar System Formation Model (Nice Model) Old view. Gas giants/comets formed near present locations (5-30 AU) and reached current orbits ~4.5 Gy ago.

    22. New Solar System Formation Model (Nice Model) Old view. Gas giants/comets formed near present locations (5-30 AU) and reached current orbits ~4.5 Gy ago.

    23. Destabilizing the Outer Solar System

    24. So far, the Nice model can explain: The orbits of the Jovian planets. The mass and orbital distribution of the Trojan asteroids, Kuiper belt objects, and irregular satellites. Why the planets (and the Moon!) experienced a “Late Heavy Bombardment” ~3.9 Gy ago. Things to Like About the Nice Model

    25. Planet Migration and the Asteroid Belt

    26. Planet Migration and the Asteroid Belt

    27. Inner Solar System Asteroids Observed asteroids with a = 2.0-5.2 AU

    28. Inner Solar System Asteroids We sub-divided them into 4 populations.

    29. Inner Solar System Asteroids 1.2 million bodies were tracked during planet migration.

    30. 1270 were captured on orbits decoupled from Jupiter. Comets in the Asteroid Belt

    31. Comets in the Asteroid Belt Many objects are unstable and escape over a few 100 My.

    32. Comets in the Asteroid Belt These captured objects were stable over 3.9 billion years.

    33. Comparison with Some Observed D-Types The orbital match with these D-type asteroids is good!

    34. Collisional Disruption of Captured Comets

    35. Micrometeorite Production Dominated By Comets Embedded in Asteroid Belt Dust production from disrupted comets dominates other main belt sources by factor of 2-4.

    36. Conclusions The parent bodies of many primitive meteorites may have originated in the outer solar system (> 15 AU) and may be related to comets and Kuiper belt objects. MB comet breakups may dominate asteroid belt dust production. This may explain why so many unmelted micrometeorites look primitive (e.g., CIs and Tagish Lake) and so few look like ordinary chondrites. Many differentiated meteorites come from parent bodies that may have formed in the terrestrial planet region (< 2 AU). Are the OCs and metamorphosed CC (e.g., CV, CO) the only meteorites indigenous to the main belt region?

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