As with other ureilites, Almahata Sitta falls on the carbonaceous chondriteCarbonaceous chondrites represent the most primitive rock samples of our solar system. This rare (less than 5% of all meteorite falls) class of meteorites are a time capsule from the earliest days in the formation of our solar system. They are divided into the following compositional groups that, other than
anhydrous mineralInorganic substance that is (1) naturally occurring (but does not have a biologic or man-made origin) and formed by physical (not biological) forces with a (2) defined chemical composition of limited variation, has a (3) distinctive set of of physical properties including being a solid, and has a (4) homogeneous
line. Although complex organicPertaining to C-containing compounds. Organic compounds can be formed by both biological and non-biological (abiotic) processes.
compounds commonly occur in many other carbonaceous chondritesChondrites are the most common meteorites accounting for ~84% of falls. Chondrites are comprised mostly of Fe- and Mg-bearing silicate minerals (found in both chondrules and fine grained matrix), reduced Fe/Ni metal (found in various states like large blebs, small grains and/or even chondrule rims), and various refractory inclusions (such
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
D- and L-aspartic acid
D- and L-glutamic acid
D- and L-serine
D- and L-threonine
D- and L-alanine
D- and L-β-amino-n-butyric acid
α- or β-aminoisobutyric 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)
POLYCYCLIC AROMATIC HYDROCARBONS