Showing papers in "Earth Moon and Planets in 1985"

The origin of selected lunar geochemical anomalies: Implications for early volcanism and the formation of light plains

Abstract: The geochemical anomalies on the eastern limb and far side of the moon are presently identified and characterized, and their formation processes are investigated, in light of Apollo spacecraft geochemical and photogeologic remote sensing data sets. The results of recent spectral reflectance studies of dark-haloed impact craters, together with considerations of anomaly surface chemistry, indicate that the geochemical anomalies associated with light plains deposits displaying dark-haloed impact craters are due to basaltic units that are either covered by varying thicknesses of highland debris or have a surface contaminated by significant amounts of highland materials.

Polarization effect on radiative transfer in planetary composite atmospheres with interacting interface

Abstract: A procedure of computing the radiance and the polarization parameters of radiation diffusely reflected and transmitted by an inhomogeneous, plane-parallel terrestrial atmosphere bounded by a ruffled ocean surface is discussed with the aid of the adding method. If the atmosphere and the ocean are simulated by a number of homogeneous sublayers, the matrices of radiation reflected and transmitted diffusely by the atmosphere-ocean system can be expressed in terms of these matrices of sublayers by using only a couple of iterative equations in which the polarity effect of radiation is included. Furthermore, the upwelling radiance and the polarization degree of radiation at the top of the atmosphere can be calculated by using a single iterative equation without requiring the equation for the diffuse transmission matrix of radiation. The ruffled ocean surface can be treated as an interacting interface, where the transmitted radiation from beneath the ocean surface into the atmosphere is also taken into account into the derivation of equations. Finally, sample computations of the upwelling radiance and the polarization degree of radiation from the top of the atmosphere are carried out at the wavelength of 0.60 micron.

Roughness of the lunar soil

Abstract: Three stereoscopic close-up photographs taken of the lunar surface by Apollo 11 and 12 astronauts were analyzed to investigate the roughness of the lunar soil at millimeter resolution. Most existing measurements of regolith roughness were based on radar measurements at wavelengths of about 8.6 mm. Several statistical parameters were determined for they landing site. The surace roughness has been found to be nearly Gaussian. The rms slopes were obtained over scales between 0.5 mm and 5 cm. They steadily decrease with increasing scale length from 58 deg to 2 deg and are in reasonable agreement with radar-measured values. The autocorrelation coefficient of the height distribution has also been obtained; it has a scale length of 0.7 mm.

Numerical simulations of collisions and gravitational encounters in systems of non-identical particles

Abstract: Numerical simulations of 200 mutually colliding non-identical particles indicate that the equipartition of random kinetic energy is possible only in systems having a narrow distribution of particle masses. Otherwise the random energy is concentrated on heavy particles. The form of the velocity distribution versus particle mass depends also on the elastic properties of the particles, and on the relative importance of the particle size. If the coefficient of restitution is a weakly decreasing function of impact velocity, a large difference in the equilibrium velocities of largest and smallest particles is possible. On the other hand, if the elasticity drops to a low level even in the small velocity regime, the dispersion of velocities is maintained by finite size and differential rotation, and the velocities of smallest particles are, at most, slightly larger than those of the largest ones. The results of simulations are consistent with the predictions of the collisional theory of non-identical particles (Hameen-Anttila, 1984). The application to Saturn's rings indicates that the geometric thickness of cm-sized particles is of the order of 50 m in the rarefied regions of the rings. Without the gravitational encounters a thickness of about 30 m is derived. These estimations are made by using the latest measurements (Bridges et al., 1984) for the restitution coefficient of icy particles.

Implications of the Galilean satellites ice envelope explosions II. The origin of the irregular satellites

Abstract: The problem of the origin of the irregular satellites is solved readily in the context of a hypothesis involving explosion of the massive ice envelopes of the Galilean satellites saturated by electrolysis products. The thrown-off unexploded (primary) ice fragments of the outermost cold layers of the envelopes are also saturated by electrolysis products. In the course of explosive ejection their internal energy increases due to shock wave heating, as a result of which they will be able to detonate in subsequent sufficiently energetic collisions. The secondary fragments from new explosions may acquire additional velocity up to a few km s−1 without breakup into small pieces.

The influence of global dust storms on the mean seasonal daily insolations at the Martian surface

Abstract: In this paper, we compare changes in the mean seasonal daily insolations at the Martian surface caused by global dust storms characterized by various atmospheric optical thickness (Τ). The calculations, made for optical depths equal to 0, 0.1, 0.5, 1.0, 2.0, and 3.0, are based on the assumption of planet encircling storms lasting one season or one year. The variations in the latitudinal and seasonal surface insolation distributions are important, mainly at the poles where e.g. the mean annual and summer daily insolations decrease by nearly a factor of 3000 as Τ goes from 0 to 3.0. At equatorial latitudes the corresponding loss is much smaller, reaching a value of approximately 40. Concerning the mean wintertime solar radiations it is found that the decrease is even more spectacular, especially at high latitudes.

Response of earth and venus ionospheres to corotating solar wind stream of 3 July 1979

Abstract: Corotating solar wind stream interactions are examined for the earth and Venus in light of data from the plasma detectors aboard ISEE-3, the Pioneer Venus Orbiter (PVO), and Helios-A, as well as in situ ion composition measurements taken by the mass spectrometers aboard the PVO and Atmosphere Explorer-E spacecraft During May-July 1979, a sequence of distinct, recurrent coronal regions developed at the sun; their analysis indicates a corresponding sequence of corotating streams Although the planetary environments are distinctly different, it is noted that pronounced and analogous ionospheric responses to the stream passage were observed at both the earth and Venus The response to the intercepted stream is consistent with independent investigations showing the importance of the variability of the solar wind momentum flux in the solar wind-ionosphere interaction at both planets

Primary and secondary magnetizations in lunar rocks - Implications for the ancient magnetic field of the Moon

Abstract: The nature of the ancient magnetic field of the Moon, in which lunar rocks acquired their remanent magnetism, has emerged as an important potential source of evidence, if somewhat controversial, for a lunar core which at a period in the Moon's history was the source of the magnetic field. Many of the lunar rocks possess a stable, primary remanence (NRM) with characteristics consistent with and indicative of thermo-remanent magnetization, acquired when the rocks cooled in an ambient magnetic field. Also present are secondary components of magnetization, one type of which appears to have been acquired between collection on the Moon and reception in the laboratory and others which were apparently acquired on the Moon. An important question to be answered is whether meteorite impacts play any part in lunar magnetism, either in modifying pre-existing magnetizations or by imparting a shock remanent magnetism (SRM) in a transient magnetic field associated with the impact. With current knowledge, SRM, in either a global lunar magnetic field of a transient field, and TRM cannot be distinguished, and in the paper the secondary magnetization characteristic of lunar rocks are examined to investigate whether their nature favours the presence of a permanent lunar magnetic field or whether they are consistent with an origin as a transient field-generated SRM. Besides terrestrial processes of secondary magnetization, such as viscous, chemical and partial thermoremanent magnetization, possible processes peculiar to the Moon are discussed and their likely importance assessed in relation to lunar sample history. The nature of the secondary magnetizations appear to be best explained on the assumption that they are due to one or more of the processes that require an ambient lunar field, namely viscous, partial thermoremanent and shock magnetization. When associated with other types of evidence obtained from lunar magnetism studies, investigations of lunar sample remanent magnetism now favours the existence of an ancient lunar magnetic field.

Bursts of Type-N in Jupiter's Decametric Radio Spectra

Abstract: Dynamic spectra of Jupiter's decametric emission often display narrow-band features, referred to as events of type N (Carr et al., 1983). The average bandwidth of these emissions is in the vicinity of 200 kHz, their durations are typically in the decasecond range, and their f-t slopes are small and random. Although the N-bursts can be described as narrow-band L-bursts, it seems that they are realted to S-bursts in their area of occurrence in the Io-B region, the durations of the emission envelopes, and their bandwidths. Possible implications are discussed.

Insolation changes on Pluto caused by orbital element variations

Abstract: In this paper, we compare changes in the insolation at Pluto, corresponding to three epochs during the dynamical history of the planet: t = − 1, 0 and 0.5, where t is the time in millions of years A.D. The two extreme values of t coincide respectively with a maximum (126 ‡) and a minimum (102 ‡) value of the obliquity (e). The other orbital elements i.e. the eccentricity (e) and the longitude of the perihelion (λp) which affect solar radiation and which are apt to significant periodic changes are also calculated for the times under consideration. In a series of figures, the combined influence of the evolving dynamic parameters on the daily insolation and on the mean (summer, winter, annual) daily insolation is illustrated.

The nature of dust grains in the comae of Comets černis and Bowell

Abstract: The currently available infrared data on scattered light from the dust comae of Cernis and Bowell set stringent upper limits to the contribution of icy grains. For Comet Cernis the data is consistent with only a 10% mass fraction of water-ice included within silicate-organic-carbon grains of scale radius 15 microns, while for Comet Bowell there is no evidence for any ice component. A coma of small (10–100Μm) organic grains containing a fraction of OH-bearing molecules that evaporate over weeks at 5 AU and leave an absorptive carbonaceous grain residue is the simplest model for Comet Bowell.

Implications of the Galilean satellites ice envelope explosions III. The origin of the Trojans and of some comets

Abstract: Secondary explosions of the primary ice fragments ejected in the explosion of the electrolyzed massive ice envelopes of the Galilean satellites are capable of imparting velocities of up to ~5km s−1 to the secondary fragments. As a result, the secondary fragments can enter the orbits of the irregular satellites (Agafonova and Drobyshevski, 1984b) and the Trojan libration orbits. In the latter case a perturbation velocity of δ V ≈ 0.3–2 km s−1 is sufficient.

Origin and early evolution of the planetary system

Abstract: It is shown by linear stability analysis that a preplanetary (presatellite) disk of dust and gas with Keplerian velocity field can become unstable due to the collective self-gravity of the disk. The radial distribution of rings, which may result from this instability, is derived. These rings later on can be the formation sites for planets around the Sun and for satellites around the planets. The derived orbits are shown to be in good agreement with that of the planets and the satellites (of Jupiter, Saturn, and Uranus). Predictions and conclusions seem to be possible for the existence of three yet unknown Uranian satellites, the origin of the early Moon and the possible radial extension of the planetary system.

Variations of the Earth's albedo deduced from the ashen light of the Moon

Abstract: An analysis of 1210 visual brightness estimations of the Moon's ashen light is presented, performed by a working group of amateur astronomers from June 1972 to December 1973. In the Moon phase interval 0.1 ⩽ Tb⩽ 0.7 the brightness expressed in a semi-empirical scale, SG, is found to be linearly related to the phase. Monthly deviations from the mean brightness show well defined winter maxima (January) and summer minima (July). Within the referenced period the brightness of the ashen light tends to increase, whereas the solar magnetic activity decreased. In addition, minor correlations and, respectively, anti-correlations are found at stratospheric temperature and, respectively density. On account of the nature of the ashen light its variations are regarded as fluctuations of the Earth's albedo.

Implications of the Galilean satellites ice envelope explosions. I: The motion of fragments inside and beyond Jupiter's sphere of action

Abstract: Explosions of the electrolyzed ice envelopes of the Galilean satellites resulted in the appearance of a large number of ice fragments deep inside Jupiter's sphere of action. Gravitational perturbations by the Galilean satellites transferred these fragments from satellite orbits into the periphery of the sphere of action and beyond it. The fragments move initially in the direction of a satellite's motion tangentially to its orbit.

Topographic Mapping of the Moon

Abstract: Contour maps of the moon have been compiled by photogrammetric methods that use stereoscopic combinations of all available metric photographs from the Apollo 15, 16, and 17 missions. The maps utilize the same format as the existing NASA shaded-relief Lunar Planning Charts (LOC-1, -2, -3, and -4), which have a scale of 1:2,750,000. The map contour interval is 500 m. A control net derived from Apollo photographs by Doyle and others was used for the compilation. Contour lines and elevations are referred to the new topographic datum of the moon, which is defined in terms of spherical harmonics from the lunar gravity field. Compilation of all four LOC charts was completed on analytical plotters from 566 stereo models of Apollo metric photographs that cover approximately 20 percent of the moon. This is the first step toward compiling a global topographic map of the moon at a scale of 1:5,000,000.

Implied origin for the craters Orcus Patera and Schiller from the lunar channel Bouvard

Abstract: Orcus Patera of Mars and Schiller of the Moon are craters with elongated configurations whose origins have remained unknown, Orcus Patera (Figure 1) has been analyzed by Greeley et al. (1978) and Schiller (Figure 2) has been studied by Offield (1971). Both concluded that the two craters were possibly some type of volcanic features. Comparative geomorphologkal analysis with the lunar channel Bouvard, however, implicates another type of origin for these craters. The lunar channel Bouvard (Figure 3) is an eroded secondary crater chain asssociated with the Orientale basin. An analogy can be drawn between the elongated shape of Bouvard and those of Orcus Patera and Schiller. It is very possible that Orcus Patera and Schiller have resulted from the erosion of aligned impact craters as has Bouvard.

Conjecture about a hurricane system in the Jovian atmosphere

Abstract: Kuiper (1972) had suggested that the Great Red Spot (GRS) of Jupiter is a giant hurricane. We present further arguments in support of this idea and propose that it may also apply to the smaller vortices such as the white and brown ovals (barges). Our estimates indicate that the spin-down time-constants for these Jovian vortices are significantly shorter than the observed lifetimes. Thus, the motions must be sustained through the continued release of internal energy. In analogy with the CISK mechanism for the terrestrial hurricane, transport of water vapor, which is observed on Jupiter, may provide the latent energy to fuel the motions. The energy the planet emits must be transported upwards; therefore its troposphere should be convectively unstable. In such an atmosphere, the proposed solar driven meridional circulation is multicellular, of the Ferrel-Thomson type. If the energy transport from the planetary interior is accelerated by the upward motions in the circulation, eastward zonal jets develop such as observed in the equatorial region. But if the upward flow of energy is impeded by the prevailing downward motions in the meridional circulation (which occur, for example, near 20‡ latitude), we propose that the convective instability is amplified. The conditions then are more favorable for the development of hurricanes which may appear in the form of the GRS and the white and brown ovals. The GRS with its large size and long life time (indicating that it is very deep) is unique, and we suggest that it may have been induced by meteor impact.

The bedrock of the vaasa circular structure, western finland

Abstract: The Vaasa circular structure (sometimes called the Soderfjarden basin) consists of roughly circular or polygonal flat cultivated ground with a diameter of 5–6 km and a surrounding bedrock ring rising 50 m above the centre of the basin and the sea. The maximum basin depth is about 300 m and is filled with Lower Cambrian sedimentary rocks with the uppermost levels being loose overburden of silts with a depth of 30 to 70 m. The surrounding bedrock consists of Precambrian mica and quartz-fieldspar gneisses, quartz- and granodiorites, and porphyritic granites. Some specimens collected from the glacial deposits depict the rocks in the centre of the Vaasa circular structure. A petrographic description of bedrock types and some glacial boulders are presented. The origin of the Vaasa circular structure is not yet solved but there are some existing theories: (1) depression formation due to tectonic movements, (2) impact cratering, and (3) volcanic cryptoexplosion. There is not any conclusive evidence found for any one of these theories and both endo- and exogenic causes must be taken into account in the form of a volcano-tectonic collapsing caldera or impact crater, respectively.

Numerical Models for the Study of Motion of Lunar Satellites

Abstract: The present study deals with numerical modeling of the elliptic restricted three-body problem as well as of the perturbed elliptic restricted three-body (Earth-Moon-Satellite) problem by a fourth body (Sun). Two numerical algorithms are established and investigated. The first is based on the method of the series solution of the differential equations and the second is based on a 5th-order Runge-Kutta method. The applications concern the solution of the equations and integrals of motion of the circular and elliptical restricted three-body problem as well as the search for periodic orbits of the natural satellites of the Moon in the Earth-Moon system in both cases in which the Moon describes circular or elliptical orbit around the Earth before the perturbations induced by the Sun. After the introduction of the perturbations in the Earth-Moon-Satellite system the motions of the Moon and the Satellite are studied with the same initial conditions which give periodic orbits for the unperturbed elliptic problem.

Survival of the Jovian planets with the Sun a Red Giant

Abstract: The survival of the Jovian planets and their satellites as the Sun becomes a Red Giant is considered. It is found that the Jovian planets would not lose any matter - not even hydrogen. The satellites would lose their gaseous or volatile envelopes. Their rocky cores would resist melting and survive. Both the planets and the satellites would be unsuited to support human life.

Some comments on `variations of the Earth's albedo deduced from the ashen light of the Moon', by Heinz Hilbrecht and Gerd Küveler

Abstract: Hilbrecht and Kiiveler (1985) have presented the results of ‘possible’ variations of the Earth’s albedo which have been deduced from the ashen light of the Moon. The observations presented in the paper were made during the period of June 1972 to December 1973. While it is acknowledged that studies of the possible variations of the Earth’s albedo are an important part of investigations of climate variations, the approach adopted by Hilbrecht and Kiiveler (lot tit) and the results presented are not sufficiently accurate for this purpose. During the early part of this century a number of astronomers made estimates of the global mean albedo of the Earth using this approach (Hunt et al., 1985). In Table I we have summarised the values that were estimated during these previous studies. The wide variation in values of the Earth’s albedo would, at first, suggest a major climatic change! However, the differences between the individual results is a direct result of the difficulties in accurately interpreting the photometric observations as a consequence of the phase ventions of the total and local regions of the Moon. The variations of the brightness of the ashen light are shown in Figure 3 of Hilbrecht and Kiiveler (lop tit). There are differences of a factor of 6 in the observations during January, March 1973 and July 1973 (see Figure 1 of Hilbrecht and Kiiveler) which will drastically affect the statistical significance of the results. Furthermore, the error bars of

Numerical Investigation of Collision Orbits of Lunar Satellites

Abstract: In the present study an investigation of the collision orbits of natural satellites of the Moon (considered to be of finite dimensions) is developed, and the tendency of natural satellites of the Moon to collide on the visible or the far side of the Moon is studied. The collision course of the satellite is studied up to its impact on the lunar surface for perturbations of its initial orbit arbitrarily induced, for example, by the explosion of a meteorite. Several initial conditions regarding the position of the satellite to collide with the Moon on its near (visible) or far (invisible) side is examined in connection to the initial conditions and the direction of the motion of the satellite. The distribution of the lunar craters-originating impact of lunar satellites or celestial bodies which followed a course around the Moon and lost their stability - is examined. First, we consider the planar motion of the natural satellite and its collision on the Moon's surface without the presence of the Earth and Sun. The initial velocities of the satellite are determined in such a way so its impact on the lunar surface takes place on the visible side of the Moon. Then, we continue imparting these velocities to the satellite, but now in the presence of the Earth and Sun; and study the forementioned impacts of the satellites but now in the Earth-Moon-Satellite system influenced also by the Sun. The initial distances of the satellite are taken as the distances which have been used to compute periodic orbits in the planar restricted three-body problem (cf. Gousidou-Koutita, 1980) and its direction takes different angles with the x-axis (Earth-Moon axis). Finally, we summarise the tendency of the satellite's impact on the visible or invisible side of the Moon.

Possible changes of the AES orbit caused by a passage through the moon's shadow

Abstract: The change in the eccentricity of the AES orbit of the type 1963-30D as a result of one passage through the Moon's shadow is estimated, and it has been shown that the effect is not negligible.

Hoyle's ice age origin: Application to Mars

Abstract: If we assume that the Martian outflow channels are result of sporadic melting of ground ice, their planet-wide distribution could imply that a sheet of ice once covered Mars. This ice sheet could have acted, in a similar manner as Hoyle's oceanic meteoric dust suspension layer model as an initiator of a Martian ice age which would be responsible for the decline of valley network formation at the end of the heavy bombardment period.

A Critique of Ramsey's Phase-Transition Hypothesis on Grounds of Comparative Planetology

Abstract: Recent interest in the Ramsey phase-transition hypothesis is examined and dicussed with reference to the ideas of plate tectonics. Modern data on the densities and likely central pressures of the terrestrial planets combined with the occurence of planetary magnetism in the Moon and Mercury are shown to conflict with the Ramsey phase-transition hypothesis.

Basin Tectonics and the Structure of the Martian Lithosphere - Results from Analysis of the Harp Map

Abstract: An analysis of the planetwide tectonic system of Mars provided by Harp (1976) reveals that the Hellas and Isidis impact basins have general tectonic systems similar to that of the Argyre impact basin. This implies that Mars does indeed have a lithospheric thickness which would have to be considered thinner than that of the Moon or Mercury but thicker than that of the Galilean satellite Callisto.

Local harmonic analysis of planetary Doppler gravity data

Abstract: Planetary gravity fields represented in terms of spherical harmonics or surface mass distributions\ do not have the necessary resolution to permit gravity analysis of local features. Doppler gravity maps representing residual line-of-sight (LOS) accelerations have much greater resolution but cannot be used for conventional geophysical analysis due to the geometric distortions inherent in LOS gravity patterns and lack of normalization of LOS data. However, LOS gravity data may be converted to vertical gravity anomalies by expressing the anomalous local gravitational potential over small rectangular areas in terms of a modified double Fourier series constrained by local Doppler gravity data. The vertical derivative of the resulting potential yields the vertical gravity components at desired altitudes. The resolution of the resulting normalized free air anomaly maps is limited only by that of the original Doppler gravity data. Extended gravity maps may be constructed this way using a moving window approach. It is anticipated that much of the lunar frontside can be mapped at resolutions ranging from 1 to 4 deg of arc.