[en] The regolith exposure history of six rocks returned by the Apollo 14, 15, and 16 missions is studied based on the cosmogenic noble gas isotopes. For each sample, the complete set of all stable noble gas isotopes and the radiaoctive isotope Kr-81 were measured. Kr-81-Kr exposure ages are calculated for rocks for which a single-stage exposure can be demonstrated. A two-stage model exposure history is derived for multistage-exposure basalt 14310 based on the amounts and isotopic ratios of the cosmogenic noble gases. The apparent Kr-81-Kr age, the depth-sensitive isostopic ratios, and fission Xe-136 results lead to the conclusion that this sample was preexposed 1.75 AE ago to cosmic rays for a duration of 350 m.y. Basalt 15058 and anorthosite 15415 also reveal multistage exposures. 44 references

[en] U-Pb age determinations on four lunar zircons from existing thin-sections of one highland breccia, 73217, using the recently constructed ion microprobe SHRIMP, are reported. The analytical reproducibility of SHRIMP is demonstrated, and procedures for measuring Pb/U, Th/U, and corecting for initial Pb are explained. Electron microprobe analyses for the zircons are also reported. The results show that the four zircons survived the lunar cataclysm without any identifiable effects on their U-Pb systematics. All four indicate a single age of 4356 +23 or -14 m.y. The zircons have experienced small variable amounts of Pb loss since crystallization, from almost zero up to about 10 percent. If this occurred during one later event, then age of the latter is between 1100 and 2300 m.y. 18 references

[en] IMP 8 observations in the geomagnetic tail of energetic particles at hundreds of keV and of the magnetic field are examined for a substorm period from 1700 to 1800 UT on March 3, 1976. For this interval, it is found that bursts of energetic protons detected at a downstream distance of approx.37 R/sub E/ in the midnight tail region are accompanied by east-west magnetic field perturbations indicative of Birkeland current sheets. The magnitude of the magnetic field perturbations ranges from approx.1 to 12 nT, corresponding to current densities of 1 to 9 mA/m when integrated over the current sheet thickness. These values are comparable to previous observations of Birkeland currents in the near-earth tail (X>-20 R/sub E/) and with the auroal-arc-assocciated Birkeland current densities at low altitudes scaled out to the tail region. The favorable comparison suggests that the closure of small-scale Birkeland current system systems, at least in these instances, lies tailward of approx.40 R/sub E/. The observed Birkeland current system and the magnitude of current densities are found to be consistent with ion tearing instability in the tail. The inferred wavelength of the tearing mode along the tail axis is approx.2 to 17 R/sub E/. In the context of the tearing model, the presence of Birkeland currents and the occasional isotropic distribution of energetic electrons (E/sub e/>0.22 MeV)= suggest that the energetic particle events in this study occur on closed magnetic field lines, even though strong tailward streaming dominates the particle anisotropy in these events

[en] Concentrations of 13 trace elements and total suspended particulates were measured for 24 consecutive days in July 1975 at Whiteface Mountain, a remote site in the Adirondack Mountains of New York. High episodic concentrations were observed during a five-day period, July 16 through 20. Air trajectory calculations showed that stagnant air masses originating southwest of Whiteface Mountain were the primary sources of these high concentrations. During July 1976 the sampling network was extended to four stations separated by hundreds of kilometers in New York State plus a site in New Jersey. Air trajectory calculations for July 19 and 20, when peak concentrations of particulates and trace metals were observed at all five stations, strongly suggest that the particulates and trace metals were transported from sources southwest of New York State

[en] The optical depths of the solar H Lyman α and the He 584-A lines in interplanetary space are calculated. From these the solar line profiles at Saturn and Uranus are determined. It is found that the solar H Lyman α line can be diminished strongly within a spectral region of vertical-barΔlambdavertical-bar<0.2 A from the line center. On the other hand, there is no significant absorption of the He 584-A line except in the downwind region where absorption occurs at Δlambdaapprox.0.04 A. The effects of solar line modification on planetary and interplanetary glow observations are discussed

[en] A new estimate of Jupiter's planetary magnetic field is obtained from the Voyager 1 observations of the Jovian magnetosphere. An explicit model for the magnetodisc current system is combined with spherical harmonic model of the planetary field with both sets of parameters determined simulataneously by using a nonlinear generalized inverse methodology. The resulting model fits the observations extremely well throughout the analysis interval (r>20 R_j). The Jovian internal field model obtained from the Voyager 1 data is very similar to the octupole Pioneer 11 models. The best fitting magnetodisc lies in the centrifugal equator, 2/3 of the way between the rotational and magnetic equators, as is appropriate for centrifugal loading of the magnetosphere by a cold plasma. No statistically significant evidence is found for secular change of the equivalent dipole estimated from Pioneer 11 (1974.9) and Voyager 1 (1979.2) data

[en] In the last 15 years, spacecraft missions to mars, especially Mariner 9 and Viking 1 and 2, have removed from discussion many of the traditional martian topics, such as canals, waves of darkening, and blue clearings. We now have a plethora of hard data about the large variety of geologic features on the planet, about the composition of the surface, the atmosphere, and the polar caps, and about many aspects of Martian meteorology, including temperatures, pressures, tides, dust storms, and the abundance and transport of water vapor. Perhaps the only areas of Martian planetology that have not been spectacularly advanced are those relating to the interior structure, the solar wind interaction, and the existence of living organisms. This paper attempts to summarize most of our new knowledge about the planet

[en] We present a new and simpler derivation of the rotational forces on minor ions in the solar wind. We show that the rotational forces can be interpreted as potential forces affecting all particles equally. As such, they do not invole interactions between different particle species and do not represent an equilibrating process

[en] Electrical-density deposition within Io is a possible mechanism for heating the interior, the source of the electrical current system being the relative motion of Io with respect of Jupiter's magnetic field. The transverse-electric mode currents circulate entirely within Io, with the frequency of Jupiter's rotation rate as observed in the Io frame. Maximum heating for Io is obtained if the electrical conductivity is 0.02 mho m^-1, a value spanned by estimates of rock conductivity for hot interiors. Under present conditions, the maximum heating available from the transverse-electric mode is some 3 orders of magnitude less than would be necessary to maintain Io's estimated heat flow. Confinement of Io's field by the external plasma would raise this estimate only moderately. The transverse-magnetic mode is effectively blocked by the cold outer surface layers, the current being bypassed by an alternative current conduction path through the ionosphere, leaving an insignificant amount in the interior. Although the transverse-magnetic heat source can be concentrated at local surface hot spots, the temperature rise is not significant on a time scale appropriate to localized heat sources. It is possible that significant heating was generated in the past by a magnetic field that was larger and had a higher frequency. Heating could have been significant also if Io's ionosphere had not been present

[en] Cross sections for the proton-induced production of radionuclides (40 less than or equal to A less than or equal to 60) from natural titanium, iron, and nickel were measured for proton energies from 80 to 200 MeV. The experimental data were compared with calculations according to Blann's hybrid model of nuclear reactions and to the semiempirical formulas of Rudstam and of Silberberg and Tsao. Based mainly on the new excitation functions, the production rates of cosmogenic radionuclides in meteorites by primary galactic protons were calculated. Since the interaction of primary solar and galactic particles with meteorites can be described with accuracy, the model calculations allow for a quantitative estimate of the action of secondary particles in meteorites. A method of completely describing the production of cosmogenic nuclides in meteorites that takes into account all sources of production is proposed. 51 references