ALBERT

Description: It is shown that N2 may be present in the troposphere of Neptune in an amount difficult to evaluate but which could easily be as high as 0.003, while there is no evidence that it is present in the atmosphere of Uranus. The estimate of the helium abundance depends on the assumed value for N2. If there is no N2 in the observed region of the atmosphere of Uranus and an N2 mole fraction of 0.003 on Neptune, the central value of the estimates of the helium abundance are equal to 0.26 by mass in both planets, which is close to the protosolar value of 0.28. This would imply that the He/H2 ratios measured in the outer atmospheres of Uranus and Neptune are representative of the ratio in the primitive solar nebula and thus were not modified during planetary formation.

Description: Spectra of the North Equatorial Belt of Jupiter were obtained in March 1992 at an unapodized resolution of 0.1/cm between 2450 and 2600/cm with the Fourier Transform Spectrometer at the 3.6 m Canada-France-Hawaii Telescope (CFHT) on Mauna Kea. Several emissions from the nu(sub 2) band of H3(+) were detected. The excitation temperature derived from the relative intensities of these emissions averaged over a wide range of longitudes is 800 +/- 100 K, and the H3(+) column density is 1.56(sup +1.0)(sub -0.5) x 10(exp 11)/sq. cm. In addition, several strong absorption features due to (13)CH4 were observed. A comparison between (12)CH4 and (13)CH4 absorptions allowed us to obtain a new measurement of the C-12/C-13 ratio. We found that this ratio, estimated for the first time in this spectral range, is 89 (+/- 25), in agreement with the terrestrial value.

Description: We study the effect of radiogenic heating due to 26Al on the thermal evolution of small icy satellites. Our object is to find the extent of internal melting as a function of the satellite radius and of the initial 26Al abundance. The implicit assumption, based on observations of young stars, is that planet and satellite accretion occurred on a time scale of approximately 10(6) yr (comparable with the lifetime of 26Al). The icy satellites are modeled as spheres of initially amorphous ice, with chondritic abundances of 40K, 232Th, 235U, 238U, corresponding to an ice/dust mass ratio of 1. Evolutionary calculations are carried out, spanning 4.5 x 10(9) yr, for different combinations of the two free parameters. Heat transfer by subsolidus convection is neglected for these small satellites. Our main conclusion is that the initial 26Al abundance capable of melting icy bodies of satellite size to a significant extent is more than 10 times lower than that prevailing in the interstellar medium (or that inferred from the Ca-Al rich inclusions of the Allende meteorite, approximately 7 x 10(-7) by mass). We find, for example, that an initial 26Al mass fraction of approximately 4 x 10(-8) is sufficient for melting almost completely icy spheres with radii of 800 km, typical of the larger icy planetary satellites. We also find that for any given 26Al abundance, there is a narrow range of radii below which only marginal melting occurs and above which most of the ice melts (and refreezes later). Since extensive melting may have important consequences, such as differentiation, gas release, and volcanic activity, the effect of 26Al should be included in future studies of satellite interiors.

Description: Since H3+ was first spectroscopically detected on Jupiter, there has been considerable interest in using this simple molecular ion to probe conditions existing in the planet's auroral regions. Here we present a series of images of Jupiter recorded at wavelengths sensitive to emission by H3+, which reveal the spatial distribution of excited H3+ molecular ions in the jovian ionosphere, as seen from Earth. We believe that they provide high-spatial-resolution images of polar aurorae on Jupiter. They suggest that the intensity of the auroral emission can vary on a timescale of an hour, a shorter period than had previously been noted. We also find that the spatial distribution of H3+ emissions correlates only partially with the loci of auroral activity inferred from ultraviolet and longer-wavelength infrared observations. The H3+ emission may therefore be controlled by auroral processes that are different from those responsible for the ultraviolet and infrared emissions.

Description: This experiment obtained imagery of the earth and the moon at a series of wavelength intervals in the near ultraviolet. These photographs were used to aid in the interpretation of the UV appearance of other planets in the solar system, especially mars and venus. The filter and film characteristics are described, as well as the ozone absorption coefficient curve.

Description: A comet-impact model for Mars uses the current atmosphere with argon as the index volatile and assumes a surface pressure of about 40 mb. The model also allows for changes in surface pressure. The model is based on analysis of gases trapped in Shergottite and Nakhlite meteorites. Tests of the model include the identification of noble gases in comets and the presence of nitrogen compounds in Jupiter identified by the Galileo probe.

Description: The chemical and isotopic composition of the Jupiter atmosphere's constituents, including their vertical variations, will be measured by the Galileo Probe Mass Spectrometer instrument through in situ sampling; batch sampling will also be undertaken for noble gas composition and isotopic ratio determinations. The instrument's gas-sampling system is connected to a quadrupole mass analyzer for molecular weight analysis. Threshold values are lowered through sample enrichment by a factor of 100-500 for stable hydrocarbons and by a factor of 10 for noble gases. The instrument follows a sampling sequence of 8192 steps, at a rate of 2 steps/sec.

Description: An experiment centering around a mass spectrometer is described, which is aimed at the identification of organic substances present in the top 10 cm of the surface of Mars and an analysis of the atmosphere for major and minor constituents as well as isotopic abundances. In addition, an indication of the abundance of water in the surface and some information concerning the mineralogy can be obtained by monitoring the gases produced upon heating the soil sample. The organic material will simply be expelled by heating to 150, 300, and 500 C into the carrier gas stream of a gas chromatograph interfaced to the mass spectrometer or by slowly heating the sample in direct communication with the spectrometer. It is planned to analyze a total of up to nine soil samples in order to study diurnal and seasonal variations. The system is designed to give useful data even for minor constituents if the total of organics should be as low as 5 ppm. The spectrometer covers the mass range of 12-200 with adequate resolution.

Description: Preliminary experiments were carried out to investigate the effectiveness of proton irradiation for producing organic chromophores. The source of the 2 MeV protons used in the experiments was a model Van de Graaff accelerator. The gas cells used were hollow aluminum cylinders. The test results show that energetic protons can be an effective energy source for the formation of complex molecules from simple ones. With the exception of sulfide compounds none of the molecules that were identified are colored. However, coloring agents could be contained in unresolvable fractions.

Description: Several models for the atmosphere of Titan have been investigated, taking into account various combinations of neon and argon. The investigation shows that the addition of large amounts of Ne and/or Ar will substantially reduce the hydrogen abundance required for a given greenhouse effect. The fact that a large amount of neon should be present if the atmosphere is a relic of the solar nebula is an especially attractive feature of the models, because it is hard to justify appropriate abundances of other enhancing agents.