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Size and density of chondrule formation regions from missing isotopic fractionation

Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander.

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Size and density of chondrule formation regions from missing isotopic fractionation

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  1. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander

  2. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander Chondrules & analogs heated in a vacuum preferentially lose their lighter isotopes, as expected (Rayleigh fractionation)

  3. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander Chondrules & analogs heated in a vacuum preferentially lose their lighter isotopes, as expected (Rayleigh fractionation) Chondrules, however, exhibit only very small fractionations!

  4. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander Chondrules & analogs heated in a vacuum preferentially lose their lighter isotopes, as expected (Rayleigh fractionation) Chondrules, however, exhibit only very small fractionations! High local vapor pressure (or total gas pressure) can erase or preclude fractionation (Alexander et al 2000, Galy et al 2000, Alexander 2004,Young & Galy 2004)

  5. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander Chondrules & analogs heated in a vacuum preferentially lose their lighter isotopes, as expected (Rayleigh fractionation) Chondrules, however, exhibit only very small fractionations! High local vapor pressure (or total gas pressure) can erase or preclude fractionation (Alexander et al 2000, Galy et al 2000, Alexander 2004,Young & Galy 2004) We present a physical model that constrains two properties of the chondrule formation region: chondrule volume densities and the size of the heated region

  6. Size and density of chondrule formation regions from missing isotopic fractionation J. Cuzzi and C. M. O’D. Alexander Chondrules & analogs heated in a vacuum preferentially lose their lighter isotopes, as expected (Rayleigh fractionation) Chondrules, however, exhibit only very small fractionations! High local vapor pressure (or total gas pressure) can erase or preclude fractionation (Alexander et al 2000, Galy et al 2000, Alexander 2004,Young & Galy 2004) We present a physical model that constrains two properties of the chondrule formation region: chondrule volume densities and the size of the heated region Scenario suggests new measurements and modeling efforts

  7. Evaporation into a vacuum: Rayleigh fractionation vth,1 and vth,2: slightly different thermal velocities for two isotopes with different masses at same T Lighter isotopes preferentially lost vth,1 x vth,1 vth,2 vth,2 sat 1,2

  8. Evaporation into a vacuum: Rayleigh fractionation vth,1 and vth,2: slightly different thermal velocities for two isotopes with different masses at same T When local xrsat fractionation is erased vth,1 sat vth,1 vth,2 vth,2 sat 1,2

  9. Evaporation into a vacuum: Rayleigh fractionation vth,1 and vth,2: slightly different thermal velocities for two isotopes with different masses at same T When local xrsat fractionation is erased vth,1 sat vth,1 vth,2 vth,2 sat 1,2

  10. Chondrule analogs show Rayleigh behavior Actual chondrules do not Cosmic spherules Rayleigh Alexander 2000, GCA Alexander et al 2000 Davis et al 2005, CPD book Cosmic spherules Alexander 2004, GCA Rayleigh Galy et al 2000 data Also: Humayan & Clayton 1995, Yu & Hewins 1997, Yu et al 1998, Nagahara & Ozawa 2000, Galy et al 2001

  11. Isolated clouds case

  12. 2 = sat Richter et al 2002

  13. 2 = sat Richter et al 2002 P > 10 bars For th= 2 x 104 sec

  14. Overlapping clouds case

  15. Overlapping clouds case R = (Dt)1/2

  16. Overlapping clouds case R = (Dt)1/2

  17. (R,t) R

  18. R1

  19. R1

  20. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2

  21. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2

  22. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2

  23. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2

  24. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2 Local P~10-3 -10-5 bar: R1 ~ 0.5-5 km; CF region 300x larger

  25. R1 Extending R integral to ∞ assumes R1 > 3-4(Dt)1/2 Local P~10-3 -10-5 bar: R1 ~ 0.5-5 km; CF region 300x larger

  26. Calibrate a from kinetic models (Alexander 2004, GCA) a~6 ± 1

  27. nc~10 m-3 Calibrate a from kinetic models (Alexander 2004, GCA) a~6 ± 1  Alexander 2004 Ebel & Grossman Wood & Hashimoto

  28. How achieve C~ 200/fc (not all solids in chondrule sizes)? Settling to midplane? h H a Turbulence diffuses particles, limits settling H/h = C = (ts /a)1/2 Dubrulle et al 1995, Cuzzi et al 1996, Cuzzi & Weidenschilling 2006

  29. How achieve C~ 200/fc (not all solids in chondrule sizes)? Settling to midplane? H a h(C=200) Particles of all sizes are melted together; and, growth time << Myr Turbulence diffuses particles, limits settling H/h = C = (ts /a)1/2 Dubrulle et al 1995, Cuzzi et al 1996, Cuzzi & Weidenschilling 2006

  30. How achieve C~ 200/fc (not all solids in chondrule sizes)? Settling to midplane? H a h(C=200) Particles of all sizes are melted together; and, growth time << Myr Turbulence diffuses particles, limits settling H/h = C = (ts /a)1/2 Dubrulle et al 1995, Cuzzi et al 1996, Cuzzi & Weidenschilling 2006

  31. Turbulence can selectively concentrate chondrule-sized precursors Concentration factor follows a probability distribution under turbulent concentration - P(>C) depends on C, P(C>200) ~ few 10-1 Cuzzi et al 2001 ApJ & work in progress

  32. Turbulence can selectively concentrate chondrule-sized precursors Concentration factor follows a probability distribution under turbulent concentration - P(>C) depends on C, P(C>200) ~ few 10-1 ? Cuzzi et al 2001 ApJ & work in progress

  33. Conclusions Chondrule precursor number densities ≥ 10 m-3 Mass enrichment factor ~ 200x over solar; Cch~ 200/fch Radius of heated volume > 150-1500km (P=10-3 -10-5 bar ) These same conditions allow stable melts, a prior concern

  34. Conclusions Chondrule precursor number densities ≥ 10 m-3 Mass enrichment factor ~ 200x over solar; Cch~ 200/fch Radius of heated volume > 150-1500km (P=10-3 -10-5 bar ) These same conditions allow stable melts, a prior concern Implications & future work Small lengthscale chondrule heating processes precluded (lightning, small planetesimal bow shocks) Problems for low-density processes (high altitude X-ray flares) Implications for redox properties from enhanced FeO, H2O Chondrule diversity from single event (nc spatial variations) correlated redox/isotopic properties where are the fractionated chondrules? Elements of differing volatility may provide more constraints Can turbulent concentration provide needed P(C,scale)?

  35. Problem for low density regime Basic criteria can be written: nc rc2 > K1 ;/rc> K2/rg For rg < 10-10,  > 2000 And since R1 > 3-4(Dt)1/2,and D =Do/rg, CFR> 1500 km

  36. Chondrules

  37. Different approach: cascade model log  Mass loading truncates TC for p >100 rg Generally consistent with p ~ rg (C ~ 200) at P( C ) ~ 0.3 for lengthscale shown (scale depends on nebula ) log  (Hogan & Cuzzi, Phys Rev subm.) log normalized eddy vorticity

  38. 2 Richter et al 2002

  39. 2 = sat Richter et al 2002

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