Shock Processing of Chondritic Material

1. Shock Processing of Chondritic Material Steve Desch (Arizona State University) Fred Ciesla (NASA Ames Research Center) Lon Hood (University of Arizona) Taishi Nakamoto (University of Tsukuba) Chondrites and the Protoplanetary Disk Kauai, Hawaii November 11, 2004

2. Motivation • Three groups calculating thermal histories of chondrules in shocks: • Nakamoto & collaborators (Iida et al. 2001 = INSN) • Desch & collaborators (Desch & Connolly 2002 = DC02) • Ciesla, Hood and collaborators (Ciesla & Hood 2002 = CH02) • Where do they agree? Where do they disagree? • Do solar nebula shock models melt chondrules in ways consistent with their petrography? • Do shocks affect other solar nebula solids?

3. Shocks in the Solar Nebula Planetesimal Bow Shocks Weidenschilling et al 1998; Hood et al 1998; Hood et al [poster, this conference] At disk midplane, but small scale (< 1000 km) Bow shock ~ 1000 km

4. Gravitational Instabilities (Spiral Shocks) Boss 2001; Nelson [poster this conference]; Moley & Durisen [poster this conference], etc. Act over entire nebula.

5. Shocks Induced by X-ray Flares Nakamoto et al 2004; Miura & Nakamoto [poster, this conference] Act only in the low-density regions high above disk shock here flares accelerate gas, which flows into disk

6. How do Shocks Work? Shocks are a “Hydrodynamic Surprise!” There is a discontinuity in gas properties C Effects of discontinuity on gas are communicated upstream at sound speed If gas is supersonic, it reaches discontinuity before hearing about it Vs

7. “SHOCK FRONT” When gas hits discontinuity, it must rapidly readjust by collisions between molecules A few mean-free-paths: < 1 m Gas is slowed by shock Supersonic w.r.t. shock front Subsonic w.r.t shock front

8. (Frame of reference of Shock Front) X V1 V2 1 2 Gas is slowed and compressed by shock Conservation of Mass d d x 1 V1 = 2 V2 ( V) = 0

9. Conservation of Momentum: d d x ( P +  V2) = 0 Gas is slowed and compressed and heated by shock Conservation of Energy: d d x [ ] 7 P 1 2  2 ( V) + V2 + FRAD = -   If not for radiation terms FRAD and , we could find V,  and P (and T!) behind shock right now

10. Line Cooling () • = rate at which gas cools by emitting “line radiation”: infrared photons emitted by water or CO molecules • INSN assume ALL line photons escape,  = Neufeld & Kaufman (1993), gas cools in ~ 10 minutes • DC02, CH02 assume NO line photons can escape (gas optically thick),  = 0 • Truth is in between;  more important at low densities

11. The Difficulty of Including Solids FRAD = Flux of (infrared) radiation emitted by solids: chondrules and dust grains -- must include to get TFINAL! Hood & Horanyi (1993), DC02 assumed FRAD =  T4 FINAL ... but that’s not right FRAD must come from radiative transfer calculation of JRAD d JRAD d  “mean intensity of radiation field” FRAD - “optical depth”

12. 1 2 JRAD() =  TINIT4 E2 (  - INIT) 1 2 +  TFINAL4 E2 ( - + FINAL) JRAD depends on TFINAL FINAL  +  T4(t) E1 | t -  | dt INIT JRAD depends on chondrule temperatures everywhere DC02 and CH02 solved for JRAD

13. Chondrule Temperatures 4a2  T4 = 4a2  JRAD + “Heating by Gas” Chondrules emit infrared and cool Chondrules exchange thermal energy with gas Chondrules heated by friction immediately after passing through shock Chondrules absorb radiation and are heated

14. gas slowed in shock front in < 1 ms 1 2 V1 V2 V2 V2 V1 V1 chondrule takes about 1 minute to slow down drag heating stage short-lived

15. Considerable Number of Feedbacks! JRAD and FRAD depend on T everywhere and TFINAL T everywhere depends strongly on JRAD TFINAL depends on FRAD TFINAL will NOT equal TAMBIENT in 1-D calculation! CH02 underestimate final T, effects of radiation DC02 overestimate final T, effects of radiation INSN do not calculate radiative transfer from solids, but do include gas radiative losses ()

16. Application to Chondrules TAMBIENT CH02

17. Radiation heats chondrule before it reaches shock TAMBIENT

18. Friction adds spike to heating while chondrule slows down (lasts about 1 minute) Radiation heats chondrule before it reaches shock

19. Friction adds spike to heating while chondrule slows down (lasts about 1 minute) Chondrule heated by radiation, hot gas, for hours

20. Chondrule heated by radiation, hot gas, for hours TFINAL TAMBIENT (CH02)

21. Cooling very rapid (~ 104 K/hr) in drag heating stage crystallization temperatures After drag heating stage, cooling takes hours because gas is hot 1 hr CH02

22. In INSN model, line emission cools gas, chondrules in ~ minutes INSN

23. Consistency with Meteoritic Record Cooling Rates Crystallization textures constrain cooling rates in crystallization temperature range 1400 - 1800 K Porphyritic chondrules: 10 - 1000 K/hr (Hewins 1996; reviewed in DC02) Barred olivine chondrules: 500 - 3000 K/hr (Connolly et al 1998; reviewed DC02) Cooling rates above liquidus (1800K) constrained to be > 5000 K/hr by retention of volatiles (Yu & Hewins 1996)

24. Cooling rates correlate with chondrule density Compound chondrules preferentially form where chondrule densities are higher Compound chondrules are ~ 70% barred olivines, cooled > 1000 K/hr Regular chondrules are ~ 85% porphyritic chondrules, cooled < 1000 K/hr After drag stage, cooling rates proportional to chondrule density in shock models (DC02, CH02)

25. Heating rate Lack of isotopic fractionation (e.g., K) constrains heating rate > 104 K/hr in temperature range 1300 - 1600 K (Tachibana et al 2004) Consistent with shocks (if TFINAL < 1100 K: not Hood & Horanyi 1993 / DC02 jump conditions) High Pressures High pressures (~ 10-3 atm) needed to suppress evaporation of Fe, etc. (e.g., Miura et al 2002)

26. Maximum Size of Chondrules Chondrules > 1 mm very rare Consistent with shocks: as melted chondrule droplets decelerate, large ones breaks apart (Susa & Nakamoto 2002) Chondrule - Matrix Complementarity Compositions of chondrules and surrounding matrix grains in OCs, CVs, CMs strongly suggest they came from same region (Wood 1985; Palme et al 1993) Thicknesses of fine-grained rims correlate with chondrule size, also suggesting chondrules and matrix grains came from same region (Morfill et al 1999)

27. Shocks & Other Solar Nebula Solids Annealing of Silicate Grains Crystalline silicate grains like those observed in comets (e.g., Wooden et al 1999) can be produced if shocks anneal amorphous grains (e.g., Harker & Desch 2002) Chemical Reactions Behind shocks, water vapor pressures elevated and kinetic rates increased, allowing formation of fine-grained phyllosilicates (Ciesla et al 2003)

28. nitrogen processed into NO, HCN, etc. Kress et al 2002

29. Summary • Differences remain among three groups: • Do line photons escape? How to implement proper jump condition for TFINAL? • INSN model tends to be more appropriate to lower densities, DC02 and CH02 to higher densities • Nonetheless, good convergence among groups • All shock models consistent with wide variety of meteoritic constraints on chondrules • Shocks very likely thermally processed chondrules, and other solar nebula solids, too