Engineering topics

Kaula, W. M.

Publications and source records attributed to Kaula, W. M..

At least 55 records · Page 3

NASA NTRS1979

Studies of oceanic tectonics based on GEOS-3 satellite altimetry

Using statistical analysis, geoidal admittance (the relationship between the ocean geoid and seafloor topography) obtained from GEOS-3 altimetry was compared to various model admittances. Analysis of several altimetry tracks in the Pacific Ocean demonstrated a low coherence between altimetry and seafloor topography except where the track crosses active or recent tectonic features. However, global statistical studies using the much larger data base of all available gravimetry showed a positive correlation of oceanic gravity with topography. The oceanic lithosphere was modeled by simultaneously inverting surface wave dispersion, topography, and gravity data. Efforts to incorporate geoid data into the inversion showed that the base of the subchannel can be better resolved with geoid rather than gravity data. Thermomechanical models of seafloor spreading taking into account differing plate velocities, heat source distributions, and rock rheologies were discussed.

Poehls, K. A.↗

NASA NTRS1979

Thermal evolution of earth and moon growing by planetesimal impacts

Improved estimates of impact energy partitioning are combined with models of planetesimal size distribution and planetary growth to infer the early thermal evolutions of the earth and moon. Binary accretion models of the moon which allow for enhancement of velocities by proximity of the earth do not get hot enough for appreciable melting unless a planetesimal mass distribution starting at a rather high value (earth mass/20 or more) is assumed. This melting occurs deeper than is inferred from petrological and thermotectonic data; hence the results favor formation of the moon as a consequence of a great impact (or great impacts) into the earth.

Kaula, W. M.↗

NASA NTRS1979

Pioneer Venus radar mapper experiment

Altimetry and radar scattering data for Venus, obtained from 10 of the first 13 orbits of the Pioneer Venus orbiter, have disclosed what appears to be a rift valley having vertical relief of up to 7 kilometers, as well as a neighboring, gently rolling plain. Planetary oblateness appears unlikely to exceed 1/2500 and may be substantially smaller.

Pettengill, G. H.↗

NASA NTRS1979

A tidal theory for the origin of the solar nebula

A model for the origin of the solar nebula is developed with attention to the significance of angular momentum considerations. Evidence that stars are born in groups rather than singly is examined. It is shown that protostars which are members of typical galactic clusters have some probability of undergoing a gravitational encounter with another star while they are collapsing. According to the model, these encounters impart disproportionate amounts of angular momentum to the later material to fall in toward already centrally condensed fragments. The amount of central condensation of a fragment is the overriding factor in determining its stability against destruction by tidal forces. The encounter also imparts angular momentum to matter that is still accreting onto the protosun.

Kobrick, M.↗

NASA NTRS1978

Geodynamic problems

The understanding of the solid earth and suggestions of what measurements should be undertaken based on estimates of instrumental feasibilities were reviewed. The observations include: (1) earth evolution and mantle convection; (2) lithosphere-asthenosphere-surface load interaction; (3) glacier-ocean-solid earth interaction; (4) solid earth interactions with the sun, moon, core, oceans, and atmosphere; (5) zones of strain accumulation; and (6) earthquakes.

Kaula, W. M.↗

NASA NTRS1977

Report of the Terrestrial Bodies Science Working Group. Volume 3: Venus

The science objectives of Pioneer Venus and future investigations of the planet are discussed. Concepts and payloads for proposed missions and the supporting research and technology required to obtain the desired measurements from space and Earth-based observations are examined, as well as mission priorities and schedules.

Kaula, W. M.↗

NASA NTRS1977

Report of the Terrestrial Bodies Science Working Group. Volume 9: Complementary research and development

Topics discussed include the need for: the conception and development of a wide spectrum of experiments, instruments, and vehicles in order to derive the proper return from an exploration program; the effective use of alternative methods of data acquisition involving ground-based, airborne and near Earth orbital techniques to supplement spacraft mission; and continued reduction and analysis of existing data including laboratory and theoretical studies in order to benefit fully from experiments and to build on the past programs toward a logical and efficient exploration of the solar system.

Fanale, F. P.↗

NASA NTRS1977

What the exploration of Mars tells us about earth

Data obtained from the Viking missions to Mars have lead to comparisons between characteristics of that planet and certain aspects of earth. Topics discussed include: thermal and compositional evolution of the planets' interiors, the origin of their atmospheres, the history of their fluid environments, the evolution of organic material, and climatic changes. Examples of convective and magmatic activity on the crusts of the two planets are contrasted; outgassing evidenced in the crustal zones is related to the evolution of atmosphere. Analysis of experimental degassing of meteorites provides further insight into the origin and composition of planetary atmospheres. Attributes of the Martian surface, which is apparently an oxidizing rather than reducing medium, are reviewed, and explanations proposed to account for its lack of an organic richness comparable to that found on earth. Data on long-range climatic changes on earth, related to precession, obliquity, and eccentricity of the planet, may contribute to understanding of the Martian polar caps, and vice versa.

Rasool, S. I.↗

NASA NTRS1977

The surface and interior of Venus

The present knowledge of Venus is reviewed with discussions of the nature and history of both the surface, crust and interior. Instrumentation on board the Pioneer Venus Orbiter, including the radar mapper, radio tracking and the fluxgate magnetometer, is described. Topographic, geological, Bouguer gravity, magnetic, and crustal thickness maps will be constructed from Orbiter data. These maps should provide information on composition and thermal history, the major geological or geophysical provinces, the rate of past and present tectonic activity, and evidence of past or present MHD dynamos.

Masursky, H.↗

NASA NTRS1977

National Geodetic Satellite Program, Part II: University of California, Los Angeles

Satellite orbit analyses are presented which were undertaken for: (1) reasons of insight and economy; (2) obtaining geophysically interesting tesseral harmonics; (3) comparing effects of tracking station location error drag, radiation pressure, and luni-solar attraction to tesseral harmonic effects; and (4) combination of satellite and terrestrial data. The analyses were divided into the following phases: (1) MINITRACK interferometry; early Baker-Nunn camera directions; (2) late Baker-Nunn camera directions; and (3) combined Baker-Nunn camera and TRANET Doppler data.

Kaula, W. M.↗

NASA NTRS1977

Mechanical processess affecting differentiation of protolunar material

Mechanisms prior to lunar formation are sought to account for the loss of volatiles, the depletion of iron, and the enrichment of plagioclase. Some of the same mechanisms are necessary to account for achondritic, stony-iron, and iron meteorites. Collisions seem marginally capable of providing the heat to accomplish the differentiation into iron, magnesian silicates, and plagioclase. Once this differentiation is accomplished, the subsequent mechanical history should have been sufficient to sort material according to composition in the protolunar circumterrestrial cloud. Effects operating include the correlation of body size with mechanical strength; the lesser ability of the cloud to trap the larger, denser infalling bodies; the more rapid drawing into the Earth of the larger moonlets; and the higher energy orbits for dominantly plagioclase smaller pieces broken off by collision.

Kaula, W. M.↗

NASA NTRS1977

On the origin of the moon, with emphasis on bulk composition

A new analysis of altimetric, gravimetric, and seismological results, together with petrological and thermal history constraints, obtains an estimated Al2O3 content of 5.0%, 2.1 times chondritic. Hence the moon definitely has a refractory lithophile excess as well as an iron deficiency. In addition, the lunar surface is characterized by refractory siderophile depletions. The combination of these properties appears to require a previous stage of differentiation in a planetary body or bodies. Siderophile and chalcolphile depletions and dispersions in eucrites suggest that these bodies are not necessarily large. Possible mechanisms of lunar formation include impacting of a very large body into the earth; tidal disruption of sizeable differentiated planetesimals by the earth; and selective capture of differentiated planetesimal material by small moonlets. Each mechanism has its difficulties; the major unknown affecting all of them is the size distribution of planetesimals.

Kaula, W. M.↗

NASA NTRS1976

Comments on the origin of Mercury

The ratio between the mass of condensed matter in Mercury's nebular zone and the final mass of condensed matter in the planet is calculated, and the result suggests that condensed matter equal to more than 10 times the planet's mass was lost from that zone. Five hypotheses to account for this loss are considered: (1) the temperature in Mercury's zone was appreciably higher than the suggested value of 1400 K, (2) the excess was expelled by solar mass outflow, (3) the excess was dragged down by the sun during its contraction, (4) the excess was knocked out by Jupiter-perturbed planetesimals, and (5) the excess was knocked out by earth- and Venus-perturbed planetesimals. The plausibility of each hypothesis is examined, and it is concluded that only planetesimal scattering by earth and Venus appears to be ruled out

Kaula, W. M.↗

NASA NTRS1975

The seven ages of a planet

On the basis of almost universally held assumptions concerning the formation of the planets and the isolation of the solar system from outside influences it follows rather plausibly that all terrestrial planets pass in principle through seven stages. The processes involved include the solidification of grains from gas in the condensation stage, planetesimal interactions, and formation processes. Vigorous convection processes lead to the gravitational separation of iron and the outgassing of oceans. Other stages are related to plate tectonics and terminal volcanism. The ultimate stage of quiescence is characterized by a thick lithosphere and no volcanism.

Kaula, W. M.↗

NASA NTRS1975

Selenodesy

Only the second- and third-degree harmonics of the global gravity field are known reliably. The most pronounced features in the near side field are still the mascons, mass excesses in ringed maria. Statistically, the magnitudes of variations in the lunar gravity field for feautres of 150- to 1100-km extent are between one-fourth and one-third those predicted from the earth on the assumption of equal stress implication. Aspects of rotational dynamics and geometry are also discussed.

Kaula, W. M.↗

NASA NTRS1975

Dynamics of lunar origin and orbital evolution

The considerable differences in bulk composition of the moon and the earth have led most investigators to favor the capture hypothesis of lunar origin. However, upon closer examination all forms of the hypothesis still seem much less plausible dynamically than formation by accretion, i.e., acquisition of the moon in many small pieces rather than as predominantly one body. Models of accretion do suggest that the proto-lunar matter had a significantly different history from the proto-earth matter. A better understanding of collisions is needed to infer the compositional consequences of this history. Recent work on the acceleration of the moon's orbit exacerbates the time scale problem of orbital evolution. However, it now is much clearer that the locus of tidal dissipation is in the oceans and hence that the solution to the time scale problem lies in differing oceanic configurations in the past.

Kaula, W. M.↗

NASA NTRS1975

Early scattering by Jupiter and its collision effects in the terrestrial zone

When Jupiter was on the order of three to ten earth masses in size, there undoubtedly was a considerably larger mass of condensed matter in its zone, since Jupiter would have perturbed most of it to other parts of the solar system. Monte Carlo studies indicate a significant portion would have crossed the earth's orbit. If the earth and moon had not yet fully formed, the probability of earth-zone planetesimals being hit by this Jupiter-scattered material was high. Further Monte Carlo models of these collisions and their products indicate a significant portion of matter was heated to melting, even if less than 5% of the relative kinetic energy went into heat. The models include capture probabilities by an embryo earth and a protolunar swarm. Because heat energy is correlated with comminution energy, and because the capture probability of the swarm is mass-dependent while embryo's is not, the protolunar material suffered much higher heating on the average than did the proto-earth material.

Kaula, W. M.↗

NASA NTRS1975

A co-accretional model of satellite formation

A model of the accumulation process of a satellite about an accreting planet is proposed in order to explain the difference in relative size between the moon and the outer planets' satellites. The parameter that most strongly affects the final mass ratio of the pair in this model is the time at which the secondary embryo is introduced. Thus the difference between terrestrial and outer planet satellite systems is easily understood in terms of the differences in Q (the specific dissipation function of the particles in the circumplanetary cloud) between these planets. The high Q of the outer planets does not allow a satellite embryo to survive a significant portion of the accretion process; therefore only small bodies formed very late in the accumulation of the planet remain as satellites.

Harris, A. W.↗