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

Motivation Three groups calculating thermal histories of chondrules in shocks: Nakamoto & collaborators (Iida et al = 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?

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

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

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 flares accelerate gas, which flows into disk shock here

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

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

11 22 V1V1 V2V2 d d x (  V) = 0  1 V 1 =  2 V 2 X Conservation of Mass (Frame of reference of Shock Front) Gas is slowed and compressed by shock

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

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

The Difficulty of Including Solids F RAD = Flux of (infrared) radiation emitted by solids: chondrules and dust grains -- must include to get T FINAL ! Hood & Horanyi (1993), DC02 assumed F RAD =  T 4 FINAL... but that’s not right F RAD must come from radiative transfer calculation of J RAD F RAD  - d J RAD d  “mean intensity of radiation field” “optical depth”

J RAD (  ) =  T INIT 4 E 2 (  -  INIT ) +  T FINAL 4 E 2 ( -  +  FINAL ) +  T 4 (t) E 1 | t -  | dt  J RAD depends on chondrule temperatures everywhere J RAD depends on T FINAL DC02 and CH02 solved for J RAD  INIT  FINAL

Chondrule Temperatures 4  a 2   T 4 = 4  a 2  J RAD + “Heating by Gas” Chondrules emit infrared and cool Chondrules absorb radiation and are heated Chondrules exchange thermal energy with gas Chondrules heated by friction immediately after passing through shock

11 22 V1V1 V2V2 gas slowed in shock front in < 1 ms V1V1 V1V1 V2V2 V2V2 chondrule takes about 1 minute to slow down drag heating stage short-lived

Considerable Number of Feedbacks! J RAD and F RAD depend on T everywhere and T FINAL T everywhere depends strongly on J RAD T FINAL depends on F RAD T FINAL will NOT equal T AMBIENT 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 (  )

Application to Chondrules CH02 T AMBIENT

Radiation heats chondrule before it reaches shock

Friction adds spike to heating while chondrule slows down (lasts about 1 minute)

Chondrule heated by radiation, hot gas, for hours

T FINAL  T AMBIENT (CH02)

CH02 Cooling very rapid (~ 10 4 K/hr) in drag heating stage After drag heating stage, cooling takes hours because gas is hot crystallization temperatures 1 hr

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

Consistency with Meteoritic Record Cooling Rates Crystallization textures constrain cooling rates in crystallization temperature range K Porphyritic chondrules: K/hr (Hewins 1996; reviewed in DC02) Barred olivine chondrules: 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)

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)

Heating rate Lack of isotopic fractionation (e.g., K) constrains heating rate > 10 4 K/hr in temperature range K (Tachibana et al 2004) Consistent with shocks (if T FINAL < 1100 K: not Hood & Horanyi 1993 / DC02 jump conditions) High Pressures High pressures (~ atm) needed to suppress evaporation of Fe, etc. (e.g., Miura et al 2002)

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)

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)

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

Summary oDifferences remain among three groups: oDo line photons escape? How to implement proper jump condition for T FINAL ? oINSN model tends to be more appropriate to lower densities, DC02 and CH02 to higher densities oNonetheless, good convergence among groups oAll shock models consistent with wide variety of meteoritic constraints on chondrules oShocks very likely thermally processed chondrules, and other solar nebula solids, too