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NASA NTRS1978

A close-up of the sun

NASA's long-range plan for the study of solar-terrestrial relations includes a Solar Probe Mission in which a spacecraft is put into an eccentric orbit with perihelion near 4 solar radii (0.02 AU). The scientific experiments which might be done with such a mission are discussed. Topics include the distribution of mass within the Sun, solar angular momentum, the fine structure of the solar surface and corona, the acceleration of the solar wind and energetic particles, and the evolution of interplanetary dust. The mission could also contribute to high-accuracy tests of general relativity and the search for cosmic gravitational radiation.

Neugebauer, M.↗

NASA NTRS1979

Skylab's Astronomy and Space Sciences

The capabilities of Skylab for multidisciplinary investigations are reviewed. Experiments and results are discussed for observations of stars and galaxies, energetic particles, interplanetary dust, Comet Kohoutek, the earth's atmosphere, and the nature and effects of space environments on man.

Lundquist, C. A.↗

NASA NTRS1978

Carbonaceous chondritic material in the solar system

Carbonaceous chondritic matrix material (CCMM) appears to be an important planet-forming unit in the mid-solar system, from the orbits of Mars to that of Uranus. The type specimen for CCMM is the low-temperature (400-500 K) assemblage of clay minerals, organic polymer, magnetite, and Ni-rich iron sulfides which constitutes the black, fine-grained matrix of primitive carbonaceous chondrites. Solar-system objects which appear to be partly or wholly made of CCMM are the satellites of Mars, most asteroids, interplanetary dust, and, perhaps, comets, satellites of the outer planets and the rings of Uranus. CCMM constituents probably formed by low-temperature reactions of higher-temperature condensates with the ambient solar composition gas, or in the case of the organic polymer, by reactions of gaseous species catalyzed by solids.

Wilkening, L. L.↗

NASA NTRS1978

COBE - Explorer of the primeval explosion

The Cosmic Background Explorer satellite will measure the diffuse microwave and infrared emission from the universe over the entire wavelength range from a few microns to 13 mm with unprecedented sensitivity and accuracy. It will measure the spectrum and angular distribution of the cosmic background radiation thought to be remnant of the big bang explosion, and it may also detect the radiation produced by the primal stars and galaxies. Furthermore, it will gather a large body of data permitting detailed study of the distribution, spectra, and temperature of the interstellar and interplanetary dust.

Mather, J. C.↗

NASA NTRS1978

New lunar microcrater evidence against a time varying meteoroid flux

An attempt to measure the relative times of formation of 25 microcraters on lunar rock 60015 is discussed which was carried out as part of a study of the flux of interplanetary dust and possible time variations of that flux over periods of 1000 to 1 million yr. The data obtained could indicate that the formation rate of 100-micron-sized pits was lower in the past as compared with the formation rate of micron-sized pits, that the flux of particles forming 100-micron-sized pits may have varied relative to that of particles forming micron-sized pits, or that 100-micron-sized pits are forming now at a higher rate, relative to the formation rate of accretionary disks, than in the past. The last suggestion is shown to be almost untenable, and the overall results are found to lead to a logical paradox. It is concluded that the attempt probably failed and that the reason for failure raises serious questions regarding the use of lunar rock surfaces as meteoroid detectors.

Hartung, J. B.↗

NASA NTRS1980

Meteoroid ablation spheres from deep-sea sediments

The paper deals with an examination of spheres that are magnetically extracted from mid-Pacific abyssal clays that are up to half a million years old. The spheres are divided into three groups using their dominant mineralogy - namely, iron, glassy, and silicate. Most spheres were formed from particles that completely melted as they separated from their parent meteoroids during the ablation process. It is concluded that the mineralogy and composition of the deep-sea spheres are identical in many respects to the meteorite fusion crusts, laboratory-created ablation debris, and the ablated interplanetary dust particles in the stratospheric collection.

Blanchard, M. B.↗

NASA NTRS1980

The Cosmic Background Explorer Satellite

The Cosmic Background Explorer (COBE) satellite, planned for launch in 1985, will measure the diffuse infrared and microwave radiation of the universe over the entire wavelength range from a few microns to 1.3 cm. It will include three instruments: a set of microwave isotropy radiometers at 23, 31, 53, and 90 GHz, an interferometer spectrometer from 1 to 100/cm, and a filter photometer from 1 to 300 microns. The COBE satellite is designed to reach the sensitivity limits set by foreground sources such as the interstellar and interplanetary dust, starlight, and galactic synchrotron radiation, so that a diffuse residual radiation may be interpreted unambiguously as extragalactic

Mather, J.↗

NASA NTRS1980

The restricted three-body problem including radiation pressure

The force of radiation pressure is included in the restricted three-body problem by considering the major radial components of the pressure force for the case of a particle in the vicinity of two luminous massive bodies, as well as by introducing the Poynting-Robertson effect for the case of one luminous body. The positions of the Lagrangian points L4 and L5 are found as functions of the ratio of radiation to gravitational forces. The Poynting-Robertson effect renders the L4 and L5 points unstable on a time scale that is long compared to the period of rotation of the two massive bodies. Implications for space colonization and a mechanism for producing azimuthal asymmetries in the interplanetary dust complex are discussed.

Schuerman, D. W.↗

NASA NTRS1980

The distribution of temperature maxima for micrometeorites decelerated in the earth's atmosphere without melting

A simple model for the statistics of heating of micrometeorites decelerated in the earth's atmosphere without melting predicts that for 10 micron particles with thermal emissivity near 1, roughly half of those with density 1 g/cc are heated above 550 C, while half of those with density 3 g/cc are heated above 800 C. In the study of stratosphere collected interplanetary dust, the model can be helpful in identifying petrographic thermometers of the atmospheric entry process, and in understanding the most recent history of this new class of extraterrestrial material available in the laboratory.

Fraundorf, P.↗

NASA NTRS1980

Deep-sea spherules from Pacific clay - Mass distribution and influx rate

From 411 kg of Pacific clay, 22 mg of stony spherules and 50 mg of iron spherules larger than 150 microns were concentrated. The extraterrestrial origin of these particles was evaluated with the aid of optical and electron microscopy and atomic absorption elemental analysis. An expression for the integral number of stony particles from this sediment in the mass range 20-300 micrograms was derived. The world-wide influx rate of stony particles in the mass range which survive atmospheric heating and ocean sediment storage is calculated to be 90 tons/yr. The relative contributions of ablation debris vs fused interplanetary dust to the influx of stony spherules is discussed, but no conclusions could be made.

Murrell, M. T.↗

NASA NTRS1980

Measurements of the cosmic background radiation

Measurements of the attributes of the 2.7-K microwave background radiation (CBR) are reviewed, with emphasis on the analytic phase of CBR studies. Methods for the direct measurement of the CBR spectrum are discussed; attention is given to receivers, antennas, absolute receiver calibration, atmospheric emission and absorption, the galactic background contribution, the analysis of LF measurements, and recent HF observations of the CBR spectrum. Measurements of the large-angular-scale intensity distribution of the CBR (the most convincing evidence that the radiation is of cosmological origin) are examined, along with limits on the linear polarization of the CBR. A description is given of the NASA-sponsored Cosmic Background Explorer (COBE) satellite mission. The results of the COBE mission will be a set of sky maps showing, in the wave number range from 1 to 10,000 kaysers, the galactic background radiation due to synchrotron emission from galactic cosmic rays, to diffuse thermal emission from H II regions, and to diffuse thermal emission from interstellar and interplanetary dust, as well as a residue consisting of the CBR and whatever other cosmological background might exist.

Weiss, R.↗

NASA NTRS1980

The effect of radiation pressure on the restricted three-body problem

The classical restricted three-body problem is extended to account for the effects of radiation pressure and the Poynting-Robertson effect on a particle with a surface-to-volume relation such that radiation pressure forces are nonnegligible moving in the gravitational field of two larger, orbiting bodies. The positions of the L4 and L5 Lagrangian points are found as functions of the ratio of radiational to gravitational forces. The inclusion of the Poynting-Robertson effect, however, is found to render the L4 and L5 points unstable on a time scale which is long compared to the rotation period of the two massive bodies. The results imply that space colonies with solar facing adjustable sails may be able to remain stationary at any heliocentric distance between a planet and the sun, and may provide a mechanism for producing asymmetries in the interplanetary dust cloud.

Schuerman, D. W.↗

NASA NTRS1981

Negative ions in comets

Negative ion sources in comets are identified and cometary plasma effects caused by negative ions are examined. The primary negative ion sources are shown to be: (1) for the inner coma - photodissociation of HCN, electron attachment of OH, and collision with alkalis; (2) in the vicinity of the nucleus - interplanetary dust collisions with the nucleus; and (3) for both the contaminated solar wind region and sporadic discharges in the nonhomogeneous inner coma plasma - dissociative electron attachment and charge inversion during keV positive ion scattering by cometary dust. Negative ion abundance for Halley's Comet has been estimated to be 10 to the -6th - 10 to the -10th of electron densities.

Wekhof, A.↗

NASA NTRS1981

Recent developments in space-borne zodiacal light photometry

The zodiacal light experiment to be flown aboard the International Solar Polar Mission in 1985 is presented. Overall objectives of the Zodiacal Light/Background Starlight Experiment include the study of the brightness, polarization, and color of the diffuse sky brightness and the determination of the spatial distributions and physical properties of the interplanetary dust as a function of spacecraft position in and out of the ecliptic. To meet these objectives, a multicolor sky-scanning photopolarimeter will be carried on the NASA spacecraft which will provide optimized stray light suppression and a capability for changing the viewing cone angle based on the use of a stepping device. Brightness and polarization measurements will be made for 11 center wavelengths in the UV and visible with 5.6 deg circular and 1.0 sq deg rectangular fields of view.

Schwehm, G. H.↗

NASA NTRS1981

The photometric center of the Gegenschein

Model calculations are employed to assess two factors that determine the position of the photometric center of the Gegenschein: (1) the increased scattering efficiency of the interplanetary dust near backscattering (at scattering angles of 165 to 180 deg); and (2) the spatial density distribution of the dust. Computer-generated brightness contours are used to examine which of these two factors dominates. It is found that the effect of the enhanced scattering of light by dust in the backscattering region is more important than the effect of the spatial density distribution of the dust. This means that the photometric center should be observed at the antisolar point at all times, except possibly when the antisolar point is at its maximum displacement from the symmetry plane.

Misconi, N. Y.↗

NASA NTRS1981

Comets and the origin of life; Proceedings of the Fifth College Park Colloquium on Chemical Evolution, University of Maryland, College Park, MD, October 29-31, 1980

Papers are presented concerning the characteristics of comets and their possible role in the origin of life. Specific topics include the characteristics, origin and structure of the cometary nucleus, cometary chemical abundances, the nature of interplanetary dust and its entry into terrestrial planet atmospheres, and the mechanism of ray closure in comet tails. Attention is also given to chemically evolved interstellar dust as a source of prebiotic material, the relation of comets to paleoatmospheric photochemistry, comets as a vehicle for panspermia, limits to life posed by extreme environments, and the status of cometary space missions as of 1980.

Ponnamperuma, C.↗

NASA NTRS1982

Science on the Space Shuttle

On the Space Shuttle's third flight, scientific instruments will study the electromagnetic environment with charging and electron beams. Beam plasma discharge will be studied. The plasma diagnostics package contains electromagnetic and particle sensors to study the ionosphere. An attempt will be made to establish a more accurate base of solar UV irradiance measurements with an absolute error of 10 percent or less over the wavelength region 120-400 nm. The solar flare X-ray polarimeter will observe flare X-rays emitted between 5 and 30 keV and measure their polarization as a function of time and photon energy. A photopolarimeter will help study zodiacal light, and interplanetary dust will be sampled by a section of thick aluminum foil. Plant seedlings will be grown to research the effect of near-zero gravity on lignification. A thermal canister experiment will help determine whether instruments can be maintained at a fixed temperature under varying thermal loads.

Neupert, W. M.↗

NASA NTRS1982

Microchrons - The Rb-87/Sr-87 dating of microscopic samples

The present investigation is concerned with the extension of the Rb-Sr dating technique to microscopic samples of individual mineral grains as small as approximately 30 micrometers in size. The measurement of the isotopic composition and the relative number of atoms of Rb and Sr has presented difficulties because of the need to separate Rb from Sr due to the isobaric interference at mass 87. This separation is critical since the changes in Sr-87/Sr-86 are directly related to the age of the sample. The approach used in the considered investigation is a modified version of the direct loading technique reported by Wasserburg et al. (1977). It is shown that measurements can be conducted of the Rb and Sr isotopic compositions and Rb/Sr atom ratios in microsamples containing 10 to the 11th to 10 to the 12th atoms of Sr. Rb-Sr model ages may prove to be of considerable importance in identifying and studying interplanetary dust particles.

Papanastassiou, D. A.↗