What Compounds Do Micrometeorites Contribute to the Atmospheres of Habitable Planets? Monika Kress, Don Brownlee Center for Astrobiology and Early Evolution & Department of Astronomy University of Washington (Seattle) George Cody Carnegie Institution of Washington 12 February 2003.

30,000,000 kg (30,000 tons) of meteorites fall to Earth every year mountain dust sand rock boulder smoke increasing particle size 0.1 mm shooting stars fireballs Anders 1989

Exogenous influx at 4 Ga would have been >> than today because: Most stars have debris disks for 300 Myr timescale ~ Late heavy bombardment Flux ~ 10 6 x today Beuzit et al, ESO/Obs. Grenoble  -Pictoris

(c) Tezel 2001 Micrometeorites are very strongly heated as they enter the atmosphere

What happens to the carbon in these strongly-heated micrometeorites? ~100  m in diameter; olivine, magnetite, glass... metal sulfide

Don Brownlee unmelted ~10  m 50%wt C

Macromolecular structure of organic component of Murchison (proxy for micrometeorites before atmospheric entry) G. Cody (GCA 2002) Carbonaceous chondrite ~5%wt C ~10%wt H 2 O

Experiment: Simulate atmospheric entry 1.Grind up bulk Murchison matrix into ~300  m particles 2.Flash-heat in pyroprobe: 500 K/sec to ~ K 3.Volatile products analyzed with GC

Products released during Murchison flash-heating experiments Major products: CO, CO 2, H 2 O (as expected) CH 4, SO 2 and H 2 S (interesting!) Other products (cool!): Hydrocarbons Numerous functionalized polycyclics (PAHs) Various heterocycles

°C/sec °C/sec Flash heating of Murchison Meteorite Powder Organics Detected Alkylbenzenes Phenol Alkylthiophenes Benzonitrile Benzothiophene Hydrocarbons Naphthalene Styrene Contaminant... GC retention time G. Cody, Carnegie

CH 4 - an important greenhouse gas in Archean and Proterozoic (and Hadean?) What are the implications for early Earth? Assume that Murchison is representative, and that 10% of the C --> CH 4 : modern CH 4 formation rate from micrometeorites ~10 8 g yr -1 compare to modern abiotic CH 4 formation rate ~10 13 g yr -1 At 4 Ga, CH 4 form. rate ~ g yr -1 (~ total modern rate)

Hydrocarbons (e.g. CH 4, C 2 H 6 ) play key role in smog/haze formation PAHs provide pre-O 3 UV protection? Disequilibrium chemistry : false positive biosignature in exoplanet atmosphere?...More implications more than just prebiotic organics!