The condensation and fractionation of refractory lithophile elements

It has long been recognized that Cr, Mg, and Si are fractionated in chondritic material along with, but to a much lesser extent than, a large group of more refractory elements. Reasoning that this might imply some unique distribution at the time of fractionation, the patterns have been reexamined. It now appears as if two distinct fractionation patterns can be resolved: one involving ordinary and enstatite chondrites and the other involving carbonaceous chondrites, the Earth, the Moon, and the eucrite parent body. Significantly, the two trends inevitably intersect at C1 composition. Ordinary and enstatite chondrites appear to have evolved from C1 composition via the removal of about 40 and 56% of a high-temperature condensate. Another high-temperature condensate, with a distinctly different composition, appears to be enriched in the carbonaceous chondrites, the Moon, and possibly the Earth, but depleted in the eucrite parent body. The compositions of these two components are constrained to fall on the appropriate mixing lines. These lines intersect the condensation path at two points, one where Mg₂SiO₄ has just begun to condense (～20%) and a second where Mg₂SiO₄ was almost completely condensed (～90%). This represents about an 80° temperature difference. But it is within this range that the largest fraction of planetary matter (Mg, Si, and Fe) condenses. Conceivably the relatively sudden appearance of large amounts of condensed material is in some way related to the fractionation process, although the exact relationship cannot be specified.     

Preirradiation history of Djermaia (H) chondritic breccia

Djermaia is a unique case among gas-rich chondrites. Twelve light xenoliths studied so far in the two available stones show unequivocal evidences of large preirradiation effects, which stand out most clearly when both cosmic-ray track and spallogenic rare-gas data are considered and compared to data from chondrites with a simple radiation history. Each of the two stones studied displays a specific xenolith population with distinct morphological and preirradiation characteristics. The first population consists of rounded and more- or less-shocked xenoliths which show evidences of short solar-flare irradiation (<1 my) and a longer residence under heavier shielding (～50 g/cm²). The second population shows neither clear indication of surface erosion nor evidence of solar-flare effects, and its preirradiation occured in deep-seated locations (～150 g/cm²).The size distribution of xenoliths is also different for the two populations, indicative of more active reworking processes in the top ～20 cm of the Djermaia regolith than at a depth of ～50 cm. The amount of ²¹Ne_sp accumulated during the preirradiation stage is substantial (25–60% of total ²¹Ne_sp), corresponding to a formal preexposure time of ～15 my for both stones, assuming static irradiation conditions. These results give an insight into the dynamics of the upper levels of the H-asteroid regolith, which appears to be in good agreement with the model of Housen, Wilkening, Chapman, and Greenberg (Icarus, 1979, 39, 317–351).     

On the nature of interstellar grains

Data on interstellar extinction are interpreted to imply an identification of interstellar grains with naturally freeze-dried bacteria and algae. The total mass of such bacterial and algal cells in the galaxy is enormous, 10⁴⁰ g. The identification is based on Mie scattering calculations for an experimentally determined size distribution of bacteria. Agreement between our model calculations and astronomical data is remarkably precise over the wavelength intervals µ^–1 < ;^–2 < 1.94µ^–1 and 2.5µ^–1 < ;^–1 < 3.0 ;^–1. Over the more restricted waveband 4000–5000 Å an excess interstellar absorption is found which is in uncannily close agreement with the absorption properties of phytoplankton pigments. The strongest of the diffuse interstellar bands are provisionally assingned to carotenoid-chlorophyll pigment complexes such as exist in algae and pigmented bacteria. The 2200 Å interstellar absorption feature could be due to degraded cellulose strands which form spherical graphitic particles, but could equally well be due to protein-lipid-nucleic acid complexes in bacteria and viruses. Interstellar extinction at wavelengths <1800 Å could be due to scattering by virus particles.     

On the possibility of submillimetric interstellar lines detection by means of laser heterodyne techniques

The search for extraterrestrial and, in particular, interstellar molecules has suddenly increased in the last ten years after the discovery of many complex organic molecules by radioastronomy. Since some very interesting lines are not detectable in the radio region, but only in the middle and far infrared, heterodyne techniques seem to be a powerful tool for interstellar line detection in the submillimetric region and the detection of CO at 870 in Orion (Philipps and Huggins, 1977) represents an encouraging success for further efforts in this new field of research. In this work the possibility of observing interstellar lines at heterodyne laser wavelengths already available in laboratory has been considered. We also computed relative intensities for some representative rotational lines of interstellar molecules at three typical temperatures (10, 20, 50 K) assuming thermodynamic equilibrium and optically thin regions. The results achieved with heterodyne laser techniques developed in the laboratory are discussed here in order to study the possibility for ground and space astronomical observations.     

The satellites of Neptune and the origin of Pluto

Pluto and the chaotic satellite system of Neptune may have originated from a single encounter of Neptune with a massive solar system body. A series of numerical experiments has been carried out to try to set limits on the circumstances of such an encounter. These experiments show that orbits very much like those of Pluto, Triton, and Nereid can result from a single close encounter of such a body with Neptune. The implied mass range and encounter velocities limit the source of the encountering body to a former trans-Neptunian planet in the 2- to 5-Earth-mass range.     

Thermodynamics of selected trace elements in the Jovian atmosphere

The thermochemistry of several hundred compounds of twelve selected trace elements (Ge, Se, Ga, As, Te, Pb, Sn, Cd, Sb, Tl, In, and Bi) has been investigated for solar composition material along a Jupiter adiabat. The results indicate that AsF₃, InBr, TlI, and SbS, in addition to CO, PH₃, GeH₄, AsH₃, H₂Se, HCl, HF, and H₃BO₃ proposed by Barshay and Lewis (1978), may be potential chemical tracers of atmospheric dynamics. The reported observations of GeH₄ is interpreted on the basis of new calculations as implying rapid vertical transport from levels where T ? 800°K. Upper limits are also set on the abundances of many gaseous compounds of the elements investigated.     

Mariner 9 ultraviolet spectrometer experiment: Vertical distribution of ozone on Mars

The vertical distribution of ozone in the atmosphere of Mars is computed from ultraviolet spectra obtained by the Mariner 9 spacecraft. In the Northern Hemisphere the ozone scale height is much smaller than the atmospheric scale height in midlatitudes and increases rapidly to a maximum farther north. At high latitudes (above 60°) there is no significant difference between the scale heights of ozone in the Northern (winter) Hemisphere and the Southern (summer) Hemisphere. Comparison of the ozone distribution with atmospheric temperature structure indicates that at some locations in the North, the density of water vapor increases with altitude, and the time for vertical mixing is about 3 days or more.     

Potential and inductive electric fields in the magnetosphere during auroras

During quiescent auroras the large-scale electric field is essentially irrotational. The volume formed by the plasma sheet and its extension into the auroral oval is connected to an external source by electric currents, which enter and leave the volume at different electric potentials and which supply sufficient energy to support the auroral activity. The location of the actual acceleration of particles depends on the internal distribution of electric fields and currents. One important feature is the energization of the carriers of the cross-tail current and another is the acceleration of electrons precipitated through relatively low-altitude magnetic-field-aligned potential drops.Substorm auroras depend on rapid and (especially initially) localized release of energy that can only be supplied by tapping stored magnetic energy. The energy is transmitted to the charged particle via electric inductive fields.The primary electric field due to changing electric currents is redistributed in a complicated way—but never extinguished—by polarization of charges. As a consequence, any tendency of the plasma to suppress magnetic-field-aligned components of the electric fields leads to a corresponding enhancement of the transverse component.     

Collision frequency and transport properties of electrons in the ionosphere

A unified ionospheric electron collision frequency model profile 〈ν_g〉 has been calculated in the height range 50–500 km. The computed profile accounts for the electron collisions with the neutral particles as well as the ions. Experimental values of momentum transfer cross-sections have been used for electron collisions with N₂, O₂ and Ar and theoretical values for N, O, He and H. It is observed that the electron-ion collisions 〈ν_ei〉 dominate over the electron-neutral collisions 〈ν_en〉 above 170 km. However, 〈ν_e?N〉 is of the same order of magnitude as 〈ν_e?O〉 in the height range 170–210 km. Above 360 km 〈ν_e?O〉 becomes more important among the neutrals. The temporal, seasonal and solar epoch variations of 〈ν_ei〉 are also shown. A typical electron collision frequency profile 〈ν_g〉 corresponding to the exospheric temperature of 1100 K has been compared with the available experimental results for D, E and F-regions obtained from different experimental techniques. This profile has been used to determine the electrical, thermal, heat flow and current flow conductivities, the mobility and the diffusivity of electrons. The results so obtained are found to be in good agreement with the earlier results.     

Plasmasphere convection patterns observed simultaneously from two ground stations

Whistler data recorded during a 14 h period on 10–11 July 1973 at Siple (L = 4.17) and Sanae (L = 3.98) have been used to compare the apparent plasma convection patterns observed from these Antarctic stations. Two distinct bulges in the plasmasphere are seen at both stations, each bulge corresponding to an apparent outflowed followed by in flow of plasma. These structures do not coincide in U.T. or M.L.T. The first bulge is seen at Siple almost 1 h earlier in M.L.T. than at Sanae and the second bulge almost 3 h earlier. This is interpreted in terms of a fairly rapid westward and inward movement of the plasmasphere structure.