During the passage of Voyager 1 through the Saturn system, the infrared instrument acquired spectral and radiometric data on Saturn, the rings, and Titan and other satellites. Infrared spectra of Saturn indicate the presence of H(2), CH(4), NH(3), PH(3), C(2)H(2), C(2)H(6), and possibly C(3)H(4) and C(3)H(8). A hydrogen mole fraction of 0.94 is inferred with an uncertainty of a few percent, implying a depletion of helium in the atmosphere of Saturn relative to that of Jupiter. The atmospheric thermal structure of Saturn shows hemisphere asymmetries that are consistent with a response to the seasonally varying insolation. Extensive small-scale latitudinal structure is also observed. On Titan, positive identifications of infrared spectral features are made for CH(4), C(2)H(2), C(2)H(4), C(2)H(6), and HCN; tentative identifications are made for C(3)H(4) and C(3)H(8). The infrared continuum opacity on Titan appears to be quite small between 500 and 600 cm(-1), implying that the solid surface is a major contributor to the observed emission over this spectral range; between 500 and 200 cm(-1) theopacity increases with decreasing wave number, attaining an optical thickness in excess of 2 at 200 cm(-1). Temperatures near the 1-millibar level are independent of longitude and local time but show a decrease of approximately 20 K between the equator and north pole, which suggests a seasonally dependent cyclostrophic zonal flow in the stratosphere of approximately 100 meters per second. Measurements of the C ring of Saturn yield a temperature of 85 +/- 1 K and an infrared optical depth of 0.09 +/- 0.01. Radiometer observations of sunlight transmitted through the ring system indicate an optical depth of 10(-1.3 +/-0.3) for the Cassini division. A phase integral of 1.02 +/- 0.06 is inferred for Rhea, which agrees with values for other icy bodies in the solar system. Rhea eclipse observations indicate the presence of surface materials with both high and low thermal inertias, the former most likely a blocky component and the latter a frost.
Twelve nonprotein amino acids appear to be present in the Murchison meteorite. The identity of eight of them has been conclusively established as Nmethylglycine, fl-alanine, 2-methylalanine, a-amino-nbutyric acid, fl-amino-n-butyric acid, 7y-amino-n-butyric acid, isovaline, and pipecolic acid. Tentative evidence is presented for the presence of N-methylalanine, N-ethylglycine, f-aminoisobutyric acid, and norvaline. These amino acids appear to be extraterrestrial in origin and may provide new evidence for the hypothesis of chemical evolution.The formation of organic compounds and their accumulation have been considered to be a necessary preamble to the appearance of life on the primordial earth (1). Various forces, such as ultraviolet light from the sun, heat from volcanos, electrical discharges in the form of lightning, and ionizing radiation from radionuclides acting upon the reducing atmosphere of the primitive earth may have produced a large number of organic compounds until the early oceans had the consistency of a "hot dilute soup" (2-5). Considerations of stellar and planetary evolution lead us to believe that the sequence of events that led to life on earth may have been duplicated elsewhere in innumerable planetary systems in the universe (6-9).In attempting to substantiate this hypothesis, two avenues have generally been used. In the synthetic approach, the conditions of a primitive planet have been simulated in the laboratory. Many of the constituents of proteins and nucleic acids have been synthesized in this manner (10,11 (19,20). The finding of amino acids indigenous to such samples would constitute convincing evidence for extraterrestrial chemical evolution. In our analysis of the Murchison meteorite we have already reported (21) the presence of five amino acids commonly found in protein: glycine, alanine, valine, proline, and glutamic acid, and two not generally found in proteins: N-methylglycine (sarcosine) and aaminoisobutyric acid (2-methylalanine). We have now identified aspartic acid and six additional nonprotein amino acids:13-alanine, a-amino-n-butyric acid, j3-amino-n-butyric acid, -y-amino-n-butyric acid, isovaline, and pipecolic acid. Furthermore, there appears to be tentative evidence for at least four other nonprotein amino acids: j3-aminoisobutyric acid, norvaline, N-methylalanine, and N-ethylglycine. ANALYSISThe amino acids were obtained from the meteorite by extraction of a pulverized sample with boiling distilled water, followed by acid hydrolysis of the aqueous extract (22). After the removal of inorganic salts from the acid hydrolysate, the resulting material was analyzed for amino acids by ion-exchange chromatography, gas chromatography, and gas chromatography combined with mass spectrometry. The residue left after the water extraction of the meteorite was hydrolyzed with acid and similarly analyzed. In a procedural blank, no amino acids could be detected.A piece of the Murchison meteorite (23) that appeared to be massive in character, and showed signs of the least exter...
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