A. Marten

Ammonia vertical density profiles in Jupiter and Saturn from their radioelectric and infrared emissivities

Abstract The distribution of ammonia with height in the atmospheres of Jupiter and Saturn has been determined by inversion of microwave thermal spectra and from spectroscopic measurements of the Jovian flux in the v 2 vibration-rotation band of NH 3 . The uncertainty in both the thermal profiles and brightness temperatures used in the inversion leads to upper and lower estimates of the retrieved NH 3 distributions. In the case of Jupiter, undersaturation of ammonia is very likely in the stratosphere and in the upper troposphere. In the lower troposphere, we find two characteristic regions with the following parameters: 1. (I) 150–175 ⩽ T ⩽ 230–250° K , 0.7 × 10 −4 ⩽ NH 3 H 2 2.0 × 10 −4 , 2. (II) T > 330–340° K , 1.2 × 10 −4 ⩽ NH 3 H 2 ⩽ 1.5 × 10 −3 . These results give further evidence for an altitude-dependent distribution of NH 3 in the deep atmosphere and for the existence of a cloud of nitrogen compounds at the bottom of region I. In the case of Saturn, a large uncertainty still exists, since the possible values of the tropospheric ammonia mixing ratio lie between 1.3 and 7.8 × 10 −4 .

The 12C/13C ratio in jupiter from the Voyager infrared investigation

The 12C/13C ratio in Jupiter has been derived from the analysis of the ν4 band of CH4 in the spectra recorded by the Voyager 1 IRIS experiment. It is found to be 160−55+40, i.e., 1.8−0.6+0.4 times the terrestrial value. Instrumental noise as well as systematic sources of error were taken into account for the estimate of the uncertainty. No plausible theory predicts such a difference between the values of the 12C/13C ratio in the inner solar system and in Jupiter. However, values of this ratio in the solar neighborhood 4.5 by ago inferred—through the use of models of chemical evolution of the Galaxy —from recent interstellar medium measurements are compatible with the present determination in Jupiter. The Jovian value, rather than the terrestrial one, could then be representative of the ratio in the primitive solar nebula.

Jupiter: New retrieved thermal profiles and ammonia distributions

Abstract New thermal profiles of Jupiter are retrieved from recent far infrared spectral measurements and for H2 mixing ratios varying from 0.8 to 0.94. The effective temperature corresponding to the inferred thermal profile is 123.15 ± 0.35°K. Far-infrared brightness temperature spectra computed from these profiles are compared to experimental data including measurements made at high spectral resolution in the NH3 ν2 band at 10 μm and in NH3 pure rotational bands between 40 and 110 μm. It is found that a strong depletion of NH3 does occur in the Jovian stratosphere and that ammonia seems to be undersaturated in the upper troposphere.

Infrared spectroscopic remote sensing from the Cassini orbiter

An infrared spectroscopy instrument for infrared remote sensing from the Cassini orbiter is being breadboarded in the laboratory. The Composite Infrared Spectrometer (CIRS) consists of a pair of Fourier Transform Spectrometers (FTS) which together cover the range from 10 - 1400/cm with a spectral resolution up to 0.5/cm. The far-infrared FTS is a polarizing interferometer covering the 10 - 300/cm range. The mid-infrared FTS is a conventional Michelson FTS covering 200 - 1400/cm in three spectral channels. CIRS will retrieve information on the atmospheres of Titan and Saturn with good vertical resolution, from deep in their tropospheres to high in their stratospheres, and into the upper few centimeters of the regoliths of icy objects. The science objectives and design of CIRS are discussed.