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.

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

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

http://www.mpi-hd.mpg.de/ion-storage/Infrared/orion.jpg

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

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

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

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

The parent bodies of meteorites: Asteroids http://www.geocities.com/zlipanov/asteroid_intro/graph.jpg

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

T = 800 K: PAHs survive over nebular timescales

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

1100 K 1000 K 900 K

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.

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 ~ 105-106 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?

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