What Compounds Do Micrometeorites Contribute to the Atmospheres of Habitable Planets?

Monika Kress, Don BrownleeCenter for Astrobiology and Early Evolution

&Department of Astronomy

University of Washington (Seattle)

George CodyCarnegie Institution of Washington

12 February 2003.

30,000,000 kg (30,000 tons) of meteorites fall to Earth every year

mountaindust sand rock bouldersmoke

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 ~ 106 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~10m50%wt C

O

OH2

O

CH3O

O

CH3

Macromolecular structure of organic component of Murchison(proxy for micrometeorites before atmospheric entry)

G. Cody (GCA 2002)

Carbonaceous chondrite~5%wt C~10%wt H2O

Experiment: Simulate atmospheric entry

1. Grind up bulk Murchison matrix into ~300 m particles

2. Flash-heat in pyroprobe: 500 K/sec to ~900-1000 K

3. Volatile products analyzed with GC

Products released during Murchison flash-heating experiments

Major products: • CO, CO2, H2O (as expected)

• CH4, SO2 and H2S (interesting!)

Other products (cool!):• Hydrocarbons • Numerous functionalized polycyclics (PAHs)• Various heterocycles

OH

S

CH3

S

S

CN

CH3

H3C

CN

S

OH

S

S

710 °C @ 500 °C/sec

610 °C @ 500 °C/sec

Flash heating of Murchison Meteorite Powder

Organics DetectedAlkylbenzenesPhenolAlkylthiophenesBenzonitrileBenzothiopheneHydrocarbonsNaphthaleneStyreneContaminant...

GC retention timeG. Cody, Carnegie

• CH4 - 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 --> CH4:

modern CH4 formation rate from micrometeorites ~108 g yr-1

compare to modern abiotic CH4 formation rate ~1013 g yr-1

At 4 Ga, CH4 form. rate ~ 1014 g yr-1 (~ total modern rate)

• Hydrocarbons (e.g. CH4, C2H6) play key role in smog/haze formation

• PAHs provide pre-O3 UV protection?

• Disequilibrium chemistry : false positive biosignature in exoplanet atmosphere?

...More implications ....

... more than just prebiotic organics!