A method for the determination of abundance ratios in the outer planets—Application to Jupiter
Abstract
A new method is defined for the determination of abundance ratios in the atmospheres of the outer planets, using visible and near-infrared spectroscopic data. We have selected a set of four conditions which determine the choice of pairs of lines (or bands) of two different species so that the scattering processes are necessarily the same for both lines. Then, the abundance ratio can be measured directly from the ratio of the absorption coefficients of these two lines and is independent from the scattering processes involved in the line formation. It is shown that the large dispersion of the "apparent abundances" measured by the RLM for CH 4 and NH 3 is actually distributed as a function of the strength of the lines, but seems much less dependent upon the wavelength. These results are then applied to the determination of 12C/ 13C, C/H, D/H, and C/N ratios in the atmosphere of Jupiter. The derived values are 12C/ 13C=89 -10+12, C/H=6.2±2.1 × 10 -4, D/H=1.3±1.0 × 10 -5, C/N=19 -7+13. In consequence, there is no evidence for enrichment in deuterium and carbon with respect to hydrogen in the Jovian atmosphere compared to the expected composition of the primordial nebula. Moreover, the strong C/N value suggests that nitrogen is trapped in condensed compounds below the NH 3 cloud, possibly in NH 4SH or aqueous ammonia solutions.
- Publication:
-
Icarus
- Pub Date:
- July 1979
- DOI:
- 10.1016/0019-1035(79)90096-4
- Bibcode:
- 1979Icar...39....1C
- Keywords:
-
- Abundance;
- Atmospheric Composition;
- Jupiter Atmosphere;
- Ammonia;
- Astronomical Models;
- Carbon Isotopes;
- Cosmology;
- Gas Giant Planets;
- Hydrogen Isotopes;
- Nitrogen