1. TFL = Terrestrial
Fractionation Line

3. Moon = Earth from
an O isotope perspective

4. Achondrite (~differentiated) meteorites
have uniform O isotopic compositions
Distinct "Parent" bodies characterized by
unique O isotopic compositions

5. Sun if addition of 16O rich material
from nearby supernova
Sun if processing of
material within proto-solar nebula

6. X-wind Model for Proto-solar nebula (Shu et al. 1996)
Figure courtesy MH Thiemens

7. Figure courtesy MH Thiemens
Photo-chemical origin: Self-shielding of CO
Self-shielded zone
[17,18O]/[16O] hu
91 – 111 nm
CO (C16O + C18O + C17O)
Immediate consequence of self-shielding: d17O/d18O = 1 fractionation line
12C17O
12C18O
12C16O
Observations:
Depletion of 13CO/12CO ratio at the edge of the cloud
Depletion of 12C18O/12C16O and 12C17O/12C16O at the edge of the cloud
Figure courtesy MH Thiemens

11. A hard job made even harder…