1. AbSciCon (Session 17): April 15, 2008.
Carbon Chemistry in Protoplanetary Disks: Quantifying the Feedstock of Habitable Planets
Dr. Monika Kress
Dept. of Physics and Astronomy
San Jose State University
Same question as for water.

2. Xander Tielens, NASA Ames
Michael Frenklach, UC Berkeley
Sean Raymond, U. Colorado
Vikki Meadows, U. Washington

3. PAHs in protoplanetary disks PAHs in meteorites
Model results: the soot line
Conclusions
pyrene

5. Disks around H Ae Be and T Tauri stars
Geers et al, A&A 2008
Disks around H Ae Be and T Tauri stars
PAHs are modified in disk environments

6. Carbon in primitive meteorites is mostly aromatic
Solid state NMR spectra for various C chondrites show that insoluble fraction is largely aromatic.
Cody & Alexander 2005

7. H2O and C in primitive meteorites
CI, CM, TL carbonaceous chondrites
~ 4% wt. carbon (bulk)
~10% water of hydration
Ordinary chondrites:
Carbon ~ 0.25%
H2O ~ 0.8%
~Same C/H2O as CI, CM, TL
CV carbonaceous chondrites
~ 0.5% wt. carbon
~0.15% water of hydration
C/H2O ~10x higher than other CC’s
Enstatite chondrites:
Carbon ~ 0.4%
H2O ~ 0

8. TL,CM,CI,CR
Wt% CK LL H L CV CO
R,EL,EH: no H2O
Wt%

9. The parent bodies of meteorites: Asteroids

10. PAH Chemistry
Well-studied under combustion conditions (P ~ 1atm, T ~ 1000 K).
Combustion kinetics model developed by M. Frenklach (UC Berkeley) for sooting flames
Considers only H, C and O
Nebular conditions (C/O <1) => PAHs do not form

11. T = 800 K: PAHs survive over nebular timescales

12. T = 1100 K. Input: Pyrene, water, CO and H2 only.
Lahuis (2007)
C2H2 ~ 10-6

13. 1100 K
1000 K
900 K

14. Meteorites agglomerated around ~1 Myr (Bell et al 1997).
time
The snow line is due to a phase transition.
~106 yr
The soot line is also due to a phase transition!
Temperature profile for disks from Bell et al 1997.

15. Conclusions
Carbon is delivered to habitable planets in the form of PAHs
Disk conditions destroy PAHs at r < ~2.5 AU
=> PAHs must have presolar heritage
High abundances of C2H2 in disks ~ years as PAHs are destroyed
=> consistent with observations of disks
=> C2H2 and CH4 : clocks, thermometers?
The “soot line” occurs where T ~ 950 K:
=> explains bulk meteorite compositions
=> possibility of C-rich worlds?

16. Cyclopropene AC3H4 Naphthalene A2 Phenanthrene A3 Benzene A1
Some important PAHs in the model
Cyclopropene
AC3H4
Naphthalene A2
Phenanthrene A3
Benzene A1
Acenaphthene
A2R5
Pyrene A4