Primordial matter in the outer solar system: A study of its chemical composition from remote spectroscopic analysis

Abstract

Our knowledge of the primordial matter from the objects of the outer solar system has made a considerable progress over the past years, in spite of the lack of any in situ measurements of these objects at the present time. The recent progress of ground-based instrumentation and the launch of the two Voyager fly-by missions have provided a huge amount of new informations about the origin and the evolution of the 'primitive' Solar System objects.The most significant discoveries concerning the atmospheres of the Giant Planets can be summarized as follows: (1) there does not seem to be any differentiation in the internal structure of Jupiter during the planet's history; thus, the H2/He ratio measured on Jupiter seems to be representative of the H/He ratio of the Primordial Nebula; (2) there is some evidence for a helium differentiation, relative to hydrogen, in Saturn's interior; (3) there seems to be a carbon enrichment on both Jupiter and Saturn by a factor about 2; this result is consistent with a model in which the planetary core is formed first, and the atmosphere accreted by this core in a second stage; (4) the D/H ratio measured on Jupiter should be representative of the D/H value in the Primordial Nebula, 4.5 billion years ago; this value is 2 to 5 times larger than the mean value measured in the local interstellar medium now; (5) Titan's atmosphere is dominated by nitrogeh and contains traces of organic and prebiotic molecules (HCN, C2N2, HC3N); the chemical composition of Titan's atmosphere could be favorable for the early stages of life development.The small bodies of the Solar System -asteroi'ds and comets -are still very poorly known. However they contain a key information about the physical and chemical properties of dust in the Primordial Nebula and the interstellar medium. With the launch of expected fly-by missions towards Comet Halley and, possibly, towards asteroids, we may hope to know a new development of our understanding of these objects, comparable to the progress we have known on the Giant Planets over the past ten years.

Origins of life: A comparison of theories and application to Mars

“…The ease with which organics could be produced under "natural" conditions suggested that they should be widespread in the cosmos. This was confirmed by direct observation of nonbiological organic material, first in carbonaceous meteorites (Kvenvolden et al, 1970) and then in the interstellar medium Knacke, 1989), comets (Kissel andKrueger, 1987), and the surfaces and atmospheres of the planets and moons of the outer solar system -particularly Titan (Encrenaz, 1984;Sagan et al, 1984;Cruikshank, 1987).…”

Mechanisms and observations for isotope fractionation of molecular species in planetary atmospheres

“…Comparison of the isotopic composition of the sun and the planets occupies an important place in the study of the origin and evolution of the solar system. This has been reviewed in detail by Encrenaz [1984] for D; the significance of the isotopic composition of N in different bodies in and outside the solar system has been reviewed by Geiss and Bochslet [1982].…”

“…The escape may be due to one of the nonthermal processes (see section 3.2) [Brinkmann, 1971;McElroy et al 1976Wallis, 1978;Dalgarno, 1980, 1983 The three elements for which isotopes have been observed (followed by the isotopes in parentheses) are H (D), C (•3C), and N (•SN). Many of these observations have been reviewed recently by Encrenaz [1984]. The importance of knowledge of the isotopic composition of their atmospheres has been emphasized by Gautier and Owen [1983a, b].…”

“…Since that time, there have been over a dozen redeterminations of D on Jupiter (in hydrogen and methane). These are summarized in Table 6; more detailed information may be found in the review by Encrenaz [1984]. The quantity of most interest is the D/H ratio in the atmosphere, rather than the HD or CH3D mixing ratios.…”

“…Ratios of •N/•'•N of compound s in Earth's atmosphere and their implications for the study of air pollution have been reviewed by Heaton [1986]. Observations of D, •3C, and •SN in the atmosphere of the outer planets have been reviewed quite recently by Encrenaz [1984]. The isotopic composition of a variety of chemical elements in the atmosphere of Venus has also been discussed by yon Zahn et at.…”