ALMAHATA SITTA ORGANICS

As with other ureilites, Almahata Sitta falls on the carbonaceous chondrite anhydrous mineral line. Although complex organic compounds commonly occur in many other carbonaceous chondrites groups, Glavin et al. (2010) conducted the first such analysis on a ureilite—Almahata Sitta. Compared to over 80 amino acids identified in some CM chondrites, only 19 amino acids and their enantiomers were identified in Almahata Sitta, along with 4 amines (produced by thermal decomposition of amino acids), plus other unidentified amino acids belonging to the 5-carbon group.

Since these organic compounds rapidly decompose at temperatures of 500–600°C, and it is generally accepted that ureilites experienced temperatures twice that, conditions for the formation of organics are tightly constrained. The amino acids could have been introduced by collisions with carbon-rich asteroids, or peak temperatures might not have been high enough to destroy them all; however, it is thought most likely that the organics were formed by catalytic reactions after asteroid 2008 TC3 had cooled.

As in all groups, these organic compounds have a nonbiogenic origin. The following organic compounds have been isolated from Almahata Sitta (Glavin et al., 2010):


ORGANIC COMPOUNDS IDENTIFIED IN THE UREILITE ALMAHATA SITTA

AMINO ACIDS

D- and L-aspartic acid
D- and L-glutamic acid
D- and L-serine
D- and L-threonine
Glycine
Tyrosine
β-alanine
D- and L-alanine
γ-amino-n-butyric acid
D- and L-β-amino-n-butyric acid
α- or β-aminoisobutyric acid
D,L-α-amino-n-butyric acid
3-amino-2,2-dimethylpropanoic acid
D,L-4-aminopentanoic acid
D,L-4-amino-3-methylbutanoic acid
D,L-3-amino-2-methylbutanoic acid
D,L-3-amino-2-ethylpropanoic acid
5-aminopentanoic acid
D,L-4-amino-2-methylbutanoic acid
3-amino-3-methylbutanoic acid
D,L-3-aminopentanoic acid
D-2-amino-2-methylbutanoic acid (D-isovaline)
L-2-amino-2-methylbutanoic acid (L-isovaline)
L-2-amino-3-methylbutanoic acid (L-valine)
D-2-amino-3-methylbutanoic acid (D-valine)
D-2-aminopentanoic acid (D-norvaline)
L-2-aminopentanoic acid (L-norvaline)
ε-amino-n-caproic acid
C5 amino acids
norleucine internal standard (IS)

AMINES

Ethanolamine
Methylamine
Ethylamine
Isopropylamine