Photochemistry in the Early Solar system: Summary of Observations and Explanations
E. D. Young
Department of Earth and Space Sciences UCLA
ÉCOLE DE PHYSIQUE Les Houches
UCLA Isotope fractionation
C16O
Reduced mass 17 controls frequency C O
Harold Urey Jacob Bigeleisen Maria Goeppert-Mayer
Harold Urey, J. Chem. Soc. (London) (1947)
J. Bigeleisen and M. G. Mayer, J. Chem. Phys. (1947)
UCLA Isotope fractionation
2 3N 3 3N 3 103 ⎛ h ⎞ ⎛ 1 1 ⎞ ⎡ a − K b − K ⎤ 17O 17O 103 ln 17/16 f , j,a f , j,b δ a − δ b ≅ α a−b = ⎜ ⎟ ⎜ − ⎟ ⎢ ∑ 2 − ∑ 2 ⎥ 24 ⎝ k T ⎠ ⎝ m m ⎠ j=1 4π j=1 4π b 16 17 ⎣⎢ ⎦⎥
2 3N 3 3N 3 103 ⎛ h ⎞ ⎛ 1 1 ⎞ ⎡ a − K b − K ⎤ 18O 18O 103 ln 18/16 f , j,a f , j,b δ a − δ b ≅ α a−b = ⎜ ⎟ ⎜ − ⎟ ⎢ ∑ 2 − ∑ 2 ⎥ 24 ⎝ k T ⎠ ⎝ m m ⎠ j=1 4π j=1 4π b 16 18 ⎣⎢ ⎦⎥
⎛ 1 1 ⎞ − 17O 17O ⎜ m m ⎟ δ a − δ b ⎝ 16 17 ⎠ Mass-dependent 18 18 = = 0.531 δ Oa − δ Ob ⎛ 1 1 ⎞ fractionation ⎜ − ⎟ ⎝ m16 m18 ⎠
UCLA Isotope fractionation
Oxygen Earth "
Moon " " ! !
, % $! )!!&.'' !+ $ #!"$!) ', & " *(, !$ *#&" $! '$#-#&!
UCLA Robert N. Clayton
1973: oxygen isotope anomaly in meteorites (CAIs)
UCLA Slope = 1.0
UCLA Magnetite + Pentlandite ( Fe O + (Fe,Ni) S ) Slope = 1.0 3 4 9 8
Sun
Chondrule
UCLA Magnetite + Pentlandite ( Fe O + (Fe,Ni) S ) Slope = 1.0 3 4 9 8
Sun
Chondrule
UCLA Fluorination data for the solar system
Slope = 1.0
UCLA Fluorination data for the solar system
Slope = 1.0
UCLA Orgueil
UCLA Planetesimal hydrology:
Halley’s
UCLA 26Al (half life = 0.7 Myr) = heat source in the early solar system
26Al 26Mg* 3 26 27 Q = 6 x10 ( Al/ Al)! exp( λt) W/kg
Water ice melts, water flows
Hydrology not unlike terrestrial water-rock systems
UCLA Kinetic models for fluid flow Temperature
Palguta (UCLA, PhD)
Δ17O
After Young et al. (1999)
UCLA Kinetic models for fluid flow
After Young et al. (1999)
UCLA Explanations:
UCLA Galactic Chemical Evolution Preserved in Dust and Gas (e.g., D.D. Clayton 1988; Jacobsen et al. 2007)
Relative to gas, i.e. the Sun!
UCLA Galactic Chemical Evolution Preserved in Dust and Gas (e.g., D.D. Clayton 1988; Jacobsen et al. 2007)
Relative to gas, i.e. the Sun!
Inconsistent with Genesis result!
UCLA Galactic Chemical Evolution Preserved in Dust and Gas (Krot et al., 2010)
Differentiated asteroids formed early but are 16O poor.
Young (2011, MetSoc)
UCLA Galactic Chemical Evolution Preserved in Dust and Gas: Dust was 16O poor? (Krot et al., 2010)
1 Original dust
?
3
2
UCLA Two-stage alternative:
3
Aqueous alteration
2
Original dust 1
UCLA Galactic Chemical Evolution or Simply Aqueous Alteration?
UCLA Intramolecular disequilibrium (Non-RRKM) effects
Mass-independent fractionation (MIF) Thiemens and others, since 1983
UCLA Intramolecular disequilibrium (Non-RRKM) effects
Thiemens (2006)
UCLA Intramolecular disequilibrium (Non-RRKM) effects
Rudolph A. Marcus proposes, with coworkers (1999 to 2004): -A mechanism for the ozone mass independent fractionation (MIF) effect -Departure from intramolecular equilibrium in the vibrationally excited state of the symmetrical isotopologue -The so-called η effect…(non RRKM) 16 16 symmetric 16 O2 16 16 16 O3*
O17 2 17 asymmetric 16 O2 16 16 O 16 O3* 3
UCLA Intramolecular disequilibrium (Non-RRKM) effects
Marcus (2004) – analogous to ozone but mediated by grain surfaces…
rock rock
k4 k4 Si16O+16O Si17,18O+16O
ksym kasym
k1 k1 16 16 16 16 17,18 17,18 16 O + Si O Si O2* O + Si O Si O O* k2 Dusty disk environment grain surfaces
UCLA Intramolecular disequilibrium (Non-RRKM) effects
Marcus (2004) – analogous to ozone but mediated by grain surfaces…
rock rock
k4 k4 Si16O+16O Si17,18O+16O
ksym kasym
k1 k1 16 16 16 16 17,18 17,18 16 O + Si O Si O2* O + Si O Si O O* k2 Dusty disk environment grain surfaces
No experimental confirmation as of yet!
UCLA UCLA z N = n (Z)dz i ∫ i 0
UCLA π e2 σν = φν fν mec
UCLA I λ (N ) o = ∏Θi i Iλ i
= ∏ exp(−τ i ) i
= ∏ exp(−σ i Ni ) i
UCLA k = J ∏ exp(−τ i ) i exp(−σ N′) k′ ∏ i i α = = i k ∏ exp(−σ i Ni′) i
UCLA UCLA CO photodissociation self shielding
o − τ Iν / Iν = e
τ C16O = 1 CO column
UV (C16O) C16O + hν C + 16O C16O
UCLA CO photodissociation self shielding
o − τ Iν / Iν = e
τ C16O = 1 τ C18O = 1 CO column
UV (C16O) C16O + hν C + 16O C16O C16O
18 18 18 18 18 18 18 18 UV (C O) C O + hν C + O C + O, O + H2 OH + H H2 O C O
No fractionation 18O enriched O ~opaque
UCLA CO photodissociation self shielding
o − τ Iν / Iν = e
τ C16O = 1 τ C18O = 1 τ C17O = 1 CO column
UV (C16O) C16O + hν C + 16O C16O C16O
18 18 18 18 18 18 18 18 UV (C O) C O + hν C + O C + O, O + H2 OH + H H2 O C O
17 17 17 17 17 17 17 17 UV (C O) C O + hν C + O C + O, O + H2 OH + H H2 O C O
No fractionation 18O, 17O enriched O ~opaque
UCLA Yurimoto and Kuramoto (2004) Lyons and Young (2005)
Clayton (2002)
Young ( 2007) UCLA Chakraborty et al. (2009)
UCLA UCLA UCLA Infamous band 31 160K
100K
UCLA Inner Edge of Disk Clayton (2002)
UCLA Inner Edge of Disk Clayton (2002)
Depletion of CO is very rapid!
UCLA ~ solar-mass star formation Molecular Cloud Yurimoto and Kuramoto (2004)
UV Dense 5 -3 cores, nH~ 10 cm Massive stars UV, CQ
UV, CO
-3 -3 nH< 10 cm Self shielding UV, CQ
UV, CO
Ionization front
Molecular cloud
UCLA Molecular Cloud
Lee et al. (2008)
UCLA Disk Surfaces
Young (2007)
UCLA Disk Surfaces
UCLA Disk Surfaces
UCLA Disk Surfaces Young (2007)
UCLA Disk Surfaces Reaction network – oxygen isotopologues 7603 reactions, 546 species, oxygen isotopologues, gas-grain reactions
UCLA Disk Surfaces Young (2007)
UCLA Calculated H2O evolution in the early solar system
Young (2007)
UCLA UCLA CO → C + O
O + H2 → OH + H OH + H → H2O
UCLA CO → C + O
O + H2 → OH + H OH + H → H2O
Equations Input transport rate constants
-7 -1 6 1 k4-1= 10 yr (10 yr OK, disk drains faster)
-5 -1 k3-4 = 10 yr (R/100 AU) (Hartmann, 2000) k4-3 = k3-4/10 (radial mixing) k3-4(H2O) > k3-4 (Cuzzi and Zahnle, 2004)
k3-2 = k2-3 ~ 1/(Ωα) (Ω = angular velocity)
2 1 -4 -1 R = 20 AU, α = 10 , (τv ) = 1x10 yr
UCLA Steady-state surface layer
Young (2007)
UCLA O 18 O = δ 17 δ
UCLA Is there a D/H signature of inward H2O migration?
Bergin (2009) Aikawa et al. (2002)
UCLA H2O gas – dust grain collision frequency Timescale for oxygen isotopic equilibration of dust
H2O gas "coll
"Diff
18 O 16O Self diffusion of O in dust grain dust grain
UCLA Timescale for oxygen isotopic equilibration of dust
H2O gas "coll
"Diff
18 O 16O τ Diff (yrs) dust grain
UCLA Timescale for oxygen isotopic equilibration of melt
-3 -4 1 mm chondrule, 10 bar total pressure, P H2O /PH2 = 2x10
H2O gas 25 "coll t total 20 Self diffusion Collisional limit "Diff (hrs) t 15 18 O 16O τ Diff (hrs) 10 dust grain O resetting timescale 5
1400 1500 1600 1700 1800 1900 2000
T (K)
UCLA CR CC EC IDP CM amino acids CM insoluble org.
Hashizumet et al. (2004)
UCLA Marty et al. (2011)
UCLA Marty et al. (2011)
UCLA Comet CN, HCN Solar wind Jupiter IDPs Earth CM organics ISM Solar Photosphere
UCLA CR CC EC IDP CM amino acids Parent body CM insoluble org.
Photochemistry
Hashizumet et al. (2004)
UCLA