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At least 1,495 records · Page 83
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NASA NTRS1982

Reconnaissance and recovery of the brighter asteroids. Brief summary of the entire project

An inexpensive method of baking large (8- by 10-inch) IIIa-J plates in 2 percent forming gas was found and successfully tested. The large storage capacity and fine grain structure of the emulsion made the sky fog negligible on plates of one-hour exposure at Link. Plates were taken through the end of October 18, 1981 on various asteroids from the recent critical lists published in the Minor Planet Circulars and the Russian Ephemeris of Minor Planets.

Edmonson, F. K.↗
NASA NTRS1981

Planets, comets, and asteroids

Methods for remote sensing of elemental composition of the surfaces of planets, comets, and asteroids are considered. The abundance of certain elements with different condensation temperatures and with various types of geochemical behavior provide data relative to the origin and evolution of these bodies. Solar X-ray fluorescence, and primary and secondary galactic cosmic ray interactions are highlighted as the major remote sensing methods.

Source record↗
NASA NTRS1982

Radar investigation of asteroids

The dual polarization CW radar system which permits simultaneous reception in the same rotational sense of circular polarization as transmitted (i.e., the "SC" sense) and in the opposite ("OC") sense, was used to observe five previously unobserved asteroids: 2 Pallas, 8 Flora, 22 Kalliope, 132 Aethra, and 471 Papagena. Echoes from Pallas and Flora were easily detected in the OC sense on each of several nights. Weighted mean echo power spectra also show marginally significant responses in the SC sense. An approximately 4.5 standard deviation signal was obtained for Aethra. The Doppler shift of the peak is about 10 Hz higher than that predicted from the a priori trial ephemeris. Calculations are performed to determine whether this frequency offset can be reconciled dynamically with optical positions reported for Aethra.

Ostro, S. J.↗
NASA NTRS1981

Minor planets and related objects. XXIX - Asteroid 29 Amphitrite

UBV photometry and lightcurves of asteroid 29 Amphitrite from all observed apparitions (March 1956-May 1977) are combined to obtain a phase function having a linear phase coefficient of 0.030 + or - 0.002 mag/deg and a mean absolute magnitude of 6.19 + or - 0.04. Amphitrite displays a reddening of its B - V color index with increasing solar phase angle: 0.816 + or - 0.004 at a phase angle of 2 deg and 0.848 + or - 0.004 at 23 deg. Since Amphitrite's orbital inclination is low (6 deg) and its lightcurve amplitudes range between 0.06 and 0.11 mag, and are well distributed in longitude, it is concluded that the obliquity of its pole is significantly different from zero. During some apparitions Amphitrite's light curves display only one maximum and minimum per 5.3904 + or - 0.007-hr rotation period while in others as many as five of each are present. This is interpreted to mean that Amphitrite has a quasi-spherical shape with a highly irregular and/or variegated surface.

Tedesco, E. F.↗
NASA NTRS1982

Radar backscattering from a rough rotating triaxial ellipsoid with applications to the geodesy of small asteroids

Radar geodesy of the asteroid 433 Eros was reported by Jurgens and Goldstein (1976). Their measurements were based on the spectral properties of a rough rotating triaxial ellipsoid. This paper presents the theory by which theoretical spectra based on a backscattering model of the form of the nth power of the cosine of theta, or any reasonable backscattering model, can be computed. Some general properties of these spectra are demonstrated, and simple measurements of the apparent radar cross section, center frequency, and effective bandwidth as a function of time are shown to be useful in determining the sizes of the semi-major axes, the exponent n in the scattering model, the backscatter efficiency of the surface material, the rotation period, and the declination of the observer above or below the rotation equator. Some of these parameters are correlated, and multiple estimation may be difficult unless the observations span a period sufficiently long so as to present a wide range of declinations of the observer. However, the departure from a spherical shape aids in separating the scattering properties from the target dimensions and facilitates the simultaneous estimation of all free parameters.

Jurgens, R. F.↗
NASA NTRS1982

Motion of the Jovian commensurability resonances and the character of the celestial mechanics in the asteroid zone - Implication for kinematics and structure

The motion of the Jovian commensurability resonances during the early evolution of the solar system induced by the dissipation of the accretion disk results in fundamental differences in the celestial mechanics of objects over which a resonance passes from that observed for a stationary resonance. Objects experiencing resonance passage acquire irreversible increases of average eccentricity to large values accounting for the present-day random velocities of the asteroids. Semi-major axes are similarly irreversibly decreased by amounts capable of clearing the Kirkwood gaps. The gap widths are in agreement with observation.

Torbett, M.↗
NASA NTRS1982

CCD scanning for asteroids and comets

The sky is to be electronically scanned for asteroids and comets that come close to the earth. This is to prevent their collision with the earth and to provide information on the origins of the solar system.

Gehrels, T.↗
NASA NTRS1982

The eight-color asteroid survey - Standard stars

Compositionally diagnostic information regarding the spectral reflectance of faint asteroids and planetary satellites, obtained using a photometric system, is presented. Standard UBV and range in effective wavelength from 0.34 to 1.04 microns are among the eight broadband filters relative to the study. An InGaAsP photomultiplier of high quantum efficiencies employed for longer wavelengths, allows work to magnitude 17 and fainter when used in conjunction with a 2 m telescope. Magnitudes and color indices with mean uncertainty + or - 0.006 mag for 50 standard stars are presented, and by setting the mean colors of four of these stars to zero, the zero point of the system is established. Sun color implications resulting from the study are U-B = 0.20 + or - 0.02, and B-V = 0.67 + or - 0.02.

Tedesco, E. F.↗
NASA NTRS1982

Calibration of the radiometric asteroid scale using occultation diameters

The paper describes a new approach to the calibration of the radiometric asteroid scale, which relies on recent accurate occultation measurements of the diameters of 2 Pallas (Wasserman et al., 1979) and 3 Juno (Millis et al., 1981), and the Voyager diameter of J4 Callisto, as well as IR photometry of these objects obtained with the NASA 3-m Infrared Telescope Facility. It is shown that this calibration is internally consistent to better than 5%, and probably has an absolute accuracy of + or - 5%. It is noted that a revision of the TRIAD radiometric diameters downward is required to bring them into agreement with the new calibration.

Telesco, C. M.↗
NASA NTRS1983

Radar observations of asteroid 1685 Toro

The present results of 13 cm wavelength radar observations of the asteroid 1685 Toro, conducted at the Arecibo Observatory in July 1980, yield radar spectra which reveal correlated and approximately twofold variations in radar cross section and spectral bandwidth as functions of rotational phase, with two maxima and two minima per rotation cycle. In combination with the photopolarimetric results of Dunlap et al. (1973), the observations presently reported offer constraints on Toro's size, shape, and surface properties. Modeling Toro as a homogeneously scattering ellipsoid yields weighed least squares estimates for the lengths of the equatorial semiaxes and a nearly Lambertian scattering law.

Ostro, S. J.↗
NASA NTRS1983

Lightcurves and phase function of asteroid 44 Nysa during its 1979 apparition

Lightcurves of asteroid 44 Nysa obtained during 20 nights in 1979 as part of a global compaign are presented. The synodic period was 6 hours and 25.3 minutes. The phase coefficient of the primary maximum was 0.026 mag/deg and the absolute V magnitude 7.05. The phase function is linear from 2 to 25 deg, no opposition effect is present.

Birch, P. V.↗
NASA NTRS1983

Pole orientation of asteroid 44 Nysa via photometric astrometry, including a discussion of the method's application and its limitations

The results of photometric astrometry, a method of determining the orientation of a rotation axis, as applied to asteroid 44 Nysa, are presented. The pole orientation of Nysa was found to be lambda(zero) = 100 deg, beta(zero) = +60 deg with an uncertainty of 10 deg. The sidereal period is 0.26755902 days + or - 0.00000006, and the rotation prograde. Refinements to, and limitations of, the application of the method of photometric astrometry are discussed. In light of the results presented herein, it is believed that all photometric astrometry pole determinations of the past should be redone.

Taylor, R. C.↗
NASA NTRS1983

Radar investigation of asteroids

For 80 Sappho, 356 Liguria, 694 Ekard, and 2340 Hathor, data were taken simultaneously in the same sense of circular polarization as transmitted (SC) as well as in the opposite (OC) sense. Graphs show the average OC and SC radar echo power spectra soothed to a resolution of EFB Hz and plotted against Doppler frequency. Radar observations of the peculiar object 2201 Oljato reveal an unusual set of echo power spectra. The albedo and polarization ratio remain fairly constant but the bandwidths range from approximately 0.8 Hz to 1.4 Hz and the spectral shapes vary dramatically. Echo characteristics within any one date's approximately 2.5-hr observation period do not fluctuate very much. Laboratory measurements of the radar frequency electrical properties of particulate metal-plus-silicate mixtures can be combined with radar albedo estimates to constrain the bulk density and metal weight, fraction in a hypothetical asteroid regolith having the same particle size distribution as lab samples.

Ostro, S. J.↗
NASA NTRS1982

Laboratory simulation of pelagic asteroidal impact Atmospheric injection, benthic topography, and the surface wave radiation field

The hypervelocity impact (1.25-6 km/s) of projectiles into water overlying unconsolidated strata is reported for a variety of water depths. Variation of the background atmospheric pressure is found to be an important additional parameter. The relation of these exploratory experiments to pelagic impact of asteroidal-sized objects is discussed from the standpoint of atmospheric injection of sea water, the modification of bottom (benthic) topography, and the generation of a field of mega-amplitude sea waves and their propagation away from the source.

Gault, D. E.↗
NASA NTRS1984

Asteroids and meteorites - Origin of stony-iron meteorites at mantle-core boundaries

Stony-iron meteorites formed at the core/mantle interfaces of small asteroidal parents. The mesosiderites formed when the thick crust of a largely molten parent body (100-200 km in diameter) foundered and sank through the mantle to the core. Pallasites formed in smaller parent bodies (50-100 km) in which olivine crystals from the partially molten mantle sank to the core/mantle interface and rafted there. Subsequent collisions stripped away the rocky mantles of both kinds of parent bodies, exposing the stony-iron surfaces of their cores to direct impacts, which continue to knock off meteorite fragments.

Greenberg, R.↗
NASA NTRS1982

Reflectance spectroscopy of diogenite meteorite types from Antarctica and their relationship to asteroids

Measurements of the spectral reflectance (0.4-2.5 microns) of three diogenite meteorites found in Antarctica are examined. Comparisons are made with previous measurements of diogenites in order to correlate the mineralogy and petrography with the spectral characteristics that can also be measured on solar system objects of unknown composition. Even though the Antarctic diogenites have the same spectral characteristics as other diogenites, there are measurable differences between all diogenite spectra. Bands caused by spin-forbidden transitions of Fe(2+) ions in pyroxene, which are identified for the first time in reflectance spectra of powdered samples, are revealed in an analysis of the spectra into sums of Gaussian components. It is shown from these laboratory measurements that spectral reflectance measurements of asteroids and other solar system objects made with the visible CVF (circular variable filter) spectrometer used for laboratory measurements can provide useful information on their surface composition.

Mcfadden, L. A.↗
NASA NTRS1984

Convex profiles from asteroid lightcurves

A lightcurve inversion method that yields a two-dimensional convex profile is introduced. The number of parameters that characterize the profile is limited only by the number of Fourier harmonics used to represent the parent lightcurve. The implementation of the method is outlined by a recursive quadratic programming algorithm, and its application to photoelectric lightcurves and radar measurements is discussed. Special properties of the lightcurves of geometrically scattering ellipsoids are pointed out, and those properties are used to test the inversion method and obtain a criterion for judging whether any lightcurve could actually be due to such an object. Convex profiles for several asteroids are shown, and the method's validity is discussed from a physical as well as purely statistical point of view.

Ostro, S. J.↗