Interstellar Chemistry recorded in Organic Matter from Primitive meteorites : Interstellar Chemistry recorded in Organic Matter from Primitive meteorites Henner Busemann, Andrea Young
Conel Alexander, Peter Hoppe1
Sujoy Mukhopadhyay, Larry Nittler
Carnegie Institute Washington
1MPI- Chemistry, Mainz
Abstract : Abstract
Where does the stuff that comes to Earth, come from? : Where does the stuff that comes to Earth, come from? Stars
– Supernovae
- AGB stars
Giant Molecular Clouds
Solar System Formation
Introduction (NJW) : Introduction (NJW) Much stuff certainly comes from stars moderately directly. E.g. small particles of diamond and silicon carbide arrive in carbonaceous meteorites, and clearly formed in the outflow from carbon stars.
Also the metals that form least volatile materials are underabundant in interstellar space.
Other evidence from interstellar medium (NJW) : Other evidence from interstellar medium (NJW) Diffuse clouds have surprising amounts of
complex organic molecules,
not just CO, CN, CS, SO but also
HCO+, HCN, HNC, C2H, C3H2, NH3 and H2CO,
There is no mechanism known to be able to form these in that low density environment,
but the molecules are known from AGB & PN outflows.
Isotopic evidence of origin : Isotopic evidence of origin Isotopes may reveal one of two different processes:
Nucleosynthesis. – material with anomalies because it originated in assorted sources.
Fractionation – material with anomalies because the isotopes were differentially apportioned between different molecular forms.
In particular, differential heats of formation are liable to be comparable with energies associated with formation mechanisms if the processes occur at LOW TEMPERATURE
How do D, N14 and N15 arise? : How do D, N14 and N15 arise? N14 and N15 are formed in the CNO bicycle
( Bethe 1938)
The relative amounts of an isotope are proportional to its lifetime in a CNO processing region of a star. There may be substantial variations in this because of changes in Temperature and Density during H burning.
Deuterium was created in the Big Bang, and has been reduced from D <4 10-6 H by processing inside stars.
How the paper starts : How the paper starts The detection of isotope anomalies
indicates that the pristine character
of the insoluble organic material
has not been completely lost.
The new material : The new material
Slide10 :
Slide11 :
Slide12 : Types of Carbonaceous Chondrite, Arrow = carbon rich CI CM CR
Slide13 :
Slide14 :
Conclusions 1 : Conclusions 1 Anomalous composition material has survived in parent bodies of primitive meteorites.
DD ~ 20x survives (1/300 H) . Cf values ~ 1/80 and even less in HCN-DCN and other interstellar organics.
Parent bodies of meteorites and comets received comparable primitive organic material
Conclusions 2 : Conclusions 2 4. CR meteorite, so far, show the greatest fraction of primitive material, but one example of a CM is comparable.
5. Tagish Lake (CM2) is oxidized, but preserves primitive “hot spots”.
The isotopic anomalies either come from cold interstellar clouds or the cold outer condensing region of the solar nebula.
The presence of interstellar grains in the meteorites show that at least some of the material did survive from interstellar space.
Conclusions 3 : Conclusions 3 8. It is not yet demonstrated whether isotopic anomalies are produced in the outer part of preplanetary disks, so we prefer interstellar origin.
9. The decoupling of the N and D enhancements imply heterogenous regions of enhancement.
10. Nucleosythesis enhancement of N15 is unlikely because it is decoupled from C12/C13.
11. Although meteorites and comets formed in different regions of the solar system, they have similar enhancements, suggesting that interstellar material survived entry into the solar nebula.
Conclusions 4 : Conclusions 4 12. The presence of the organic matter shows that in the region where these meteorites formed, the temperature did not get high.
13. Radial mixing of material is suggested by observation of crystalline silicates in these meteorites and in cometary dust. (?NJW)
14. Isotopic imaging together with C/H ratios suggest that the CH ratios and D and N isotopic enrichment are uncoupled. At least three components with distinct origin seem to be present.
Comments by B. Marty : Comments by B. Marty Marty does not like the idea that the solar nebula left substantial material unchanged. He states without demonstration that the material that went into planets and meteorites was well mixed.
He argues this from the presence of the CAIs and chondrules, but this only shows that some of the material was changed by the solar nebula.
Marty states that D enhancement in carbonaceous material increases as the bonds to C are weaker. This suggests that the D enhancement occurs after the molecules were formed, but has no bearing on whether it was before or after initiation of the solar nebula.