Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “asteroids”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Is 1220 Crocus a precessing, binary asteroid?

Photoelectric data of the asteroid 1220 Crocus over a 13 night period in 1984 revealed the presence of two separate periods. The light curves were indicative of a precessing body, but not one in free precession due to motions induced by a collision. Closer examinations revealed periods of 30.7 and 7.9 hr with amplitudes of 0.87 and 0.15 mag, respectively. An analysis of the source of an external torque which could be causing a forced precession led to the hypothesis that 1220 Crocus has a satellite. Verification of the binary asteroid configuration will depend on more detailed light curves, the possible modulation of the shorter period by the longer, and possible use of the Space Telescope.

Binzel, R. P.↗
NASA NTRS1985

Submillimeter observations of the asteroid 10 Hygiea

The first successful ground-based observations of any asteroid at submillimeter wavelengths are reported. Observations of the asteroid 10 Hygiea at 370 and 770 micrometers are combined with observations in the near and thermal infrared (2.2, 10.6, and 21 micrometers) to study the thermal properties of Hygiea's regolith. The 'standard' (nonrotating) thermal model is consistent with the entire data set, although a rotating thermophysical model with a 'lunarlike' thermal inertia cannot be ruled out.

Lebofsky, L. A.↗
NASA NTRS1985

Ellipsoidal geometry in asteroid thermal models - The standard radiometric model

The major consequences of ellipsoidal geometry in an othewise standard radiometric model for asteroids are explored. It is shown that for small deviations from spherical shape a spherical model of the same projected area gives a reasonable aproximation to the thermal flux from an ellipsoidal body. It is suggested that large departures from spherical shape require that some correction be made for geometry. Systematic differences in the radii of asteroids derived radiometrically at 10 and 20 microns may result partly from nonspherical geometry. It is also suggested that extrapolations of the rotational variation of thermal flux from a nonspherical body based solely on the change in cross-sectional area are in error.

Brown, R. H.↗
NASA NTRS1985

Radar observations of asteroids and comets

Radar techniques for the observation of asteroids and comets are reviewed, emphasizing the logical basis for inferring physical properties from radar measurements. Results to date are reviewed, focusing on some recent highlights of the research to demonstrate the synergism between radar and other ground-based techniques. Particular attention is given to the asteroids 2 Pallas, 16 Psyche, 2101 Adonis, and the comet IRAS-Araki-Alcock.

Ostro, S. J.↗
NASA NTRS1986

Planet-Crossing Asteroid Search (PCAS)

511 independent fields were photographed with the 0.46m Schmidt during 15 observing runs along with a limited number of 1.2m Schmidt exposures. From these fields 122 new asteroids were reported. Special sets of field using the 1.2m Schmidt are continuing to yield numerous new faint asteroids. The combined result from both telescopes include 4 Mars-crossers, 3 Hungarias, 2 Phocaeas, a unique high inclination object (1985XB), 1 Apollo (1985PA) and Aten (3362) Khufu. Halley was regularly monitored (astrometry and large-scale phenomena) IHW participation. Scientifically value photographs were obtained from both 0.46m and 1.2m Schmidt Telescopes. Other accessible comets were observed including G-Z. Recently a new comet (1986d) was discovered.

Helin, E. F.↗
NASA NTRS1986

Passive microwave remote sensing of the asteroids using the VLA: Continuation

The structure and composition parameters for a selected set of the main belt asteroids were inferred by employing microwave remote sensing techniques developed for Earth observations. Precise flux density measurements made with the Very Large Array (VLA) and the 11 m mm-wave antenna of the National Radio Astronomy Observatory are used to define the microwave continuum spectra of these asteroids. These spectra were inverted in order to estimate the near-surface bulk properties (radii, roughness, composition) independent of previous optical or infrared spectroscopy.

Webster, W. J., Jr.↗
NASA NTRS1987

Computer simulations of 10-km-diameter asteroid impacts into oceanic and continental sites: Preliminary results on atmospheric passage, cratering and ejecta dynamics

A series of analytical calculations of large scale cratering events for both oceanic and continental sites were made in order to examine their effects on the target media and atmosphere. The first analytical studies that were completed consists of computer simulations of the dynamics of: (1) the passage of a 10 km diameter asteroid moving at 20 km/sec through the Earth's atmosphere, and (2) the impact cratering events in both oceanic and continental environments. Calculation of the dynamics associated with the passage of the asteroid through the atmosphere showed strong effects on the surrounding air mass. The calculations of the impact cratering events showed equally dramatic effects on the oceanic and continental environments. These effects are briefly discussed.

Roddy, D. J.↗
NASA NTRS1986

A comparison of the continuum colors of P/Halley, other comets, and asteroids

Early observations (1985 Feb.) of P/Halley were made with broadband BVJK filters when a substantial fraction of the light came from the nucleus; the resulting colors appear red, but with signal-to-noise ratios less than or = 5. More recent observations were made with the narrower International Halley Watch continuum filters when the light from the comet is dominated by the coma. The colors over the wavelength range 0.3 to 0.7 microns are more neutral. Continuum colors were also observed for other comets. All show moderately red to very red colors that can be best matched by asteroids of the P and D spectral classes, suggesting that the refractory component of comets is similar to that of the more distant asteroids.

Tholen, D. J.↗
NASA NTRS1986

Scaling laws for the catastrophic collisions of asteroids

Collisions of asteroids have traditionally been studied through laboratory experiments involving targets with masses some 15 to 20 orders of magnitude less than the bodies they are intended to simulate. Here the problem of extrapolation of experimental results up to the size regimes of interest is considered. Scaling relations are developed for the shattering threshold and the size and velocity distributions of collisional fragments. A methodology which has often been used assumes that collisional outcomes (e.g., the size of the largest remaining fragment) are completely characterized by Q, the kinetic energy of the impactor normalized by the mass of the target body. This scaling is shown to be an unlikely special case of a more general scaling theory which indicates that collisional outcomes should depend on target size and encounter velocity, even when Q is held constant. In particular, as target size increases, the critical value of Q required to shatter a body, and the characteristic fragment velocities should initially decrease (in qualitative agreement with the recent model of Farinella et al., 1982) up to an asteroid size of perhaps 40 to 50 km; then, as the gravitational forces start to dominate, the value of Q will again increase (in qualitative agreement with the recent model of Davis et al., 1983 and 1985).

Holsapple, K. A.↗
NASA NTRS1986

Catastrophic disruption in the solar system - Asteroid collisional history, origin of Hirayama families and disruption of small satellites

The process of collisional catastrophic disruption has played a significantly role in structuring the solar system. Diverse populations of bodies such as the asteroid belt, small satellites of Jupiter and Saturn and perhaps even the rings of Saturn have been created or substantially changed by catastrophic distruption. Understanding the outcome of large scale impacts is essential to learning about the early history of the solar system in the asteroid zone and the reason why a planet failed to form there.

Davis, D. R.↗
NASA NTRS1986

Asteroid lightcurve studies

The use of light curves to characterize the dynamics of asteroids is discussed in a review of recent statistical and theoretical investigations. The summary, detailed, and bibliographic lists comprising the IAU light-curve data set are briefly characterized, and studies of rotation rates, shapes and pole positions, and phase relations are surveyed. Rotation-rate differences among the taxonomic classes and with asteroid size are noted, along with a wide dispersion of rotation rates in objects smaller than about 100 km.

Harris, A. W.↗
NASA NTRS1986

Cometary nuclei and asteroids - Has a link been found?

Data from recent spectrophotometric observations of cometary dust are summarized and compared with similar data on asteroids. A number of systematic similarities are noted between comet materials and dark reddish-black asteroids such as the Trojans. It is suggested that Trojans and comet nuclei are members of a class of outer-solar-system planetesimals with colors due to opaque carbonaceous dust containing reddish low-temperature organic condensates.

Hartmann, W. K.↗
NASA NTRS1986

Speckle interferometry of asteroids. III - 511 Davida and its photometry

Photometric interferometry data on the fifth largest minor planet, 511 Davida, are used to generate orbital elements and physical dimensions. The Seward 2.3 m telescope was employed to obtain the speckle interferometric data. The asteroid was assumed to be a uniform-surfaced triaxial ellipsoid rotating about its shortest axis. A simultaneous amplitude-magnitude aspect method is defined for determining the pole position of the object, which is calculated to be within 4 deg of (307 deg; +32). A weighted amplitude aspect relation provides similar data. The albedos are estimated to lie within the range 0.24-0.42, and an a/b axial ratio of 0.97-1.66 is projected. The variations in the photometric albedos are taken as evidence of a nonuniform surface, a conclusion similar to that reached after earlier photometric measurements of the asteroid Herculina.

Drummond, J. D.↗
NASA NTRS1987

Original structures, and fragmentation and reassembly histories of asteroids - Evidence from meteorites

The validity of an onion shell model (OSM) for chondrite parent asteroids was assessed using metallographic cooling rates (MCR) derived from the compositions of metallic Fe-Ni grains. The hypothesis evaluated was that the hottest materials in chondrites would have been buried the deepest and cooled the slowest. The survey covered breccia from regolith and 13 different chondrites. The MCRs agreed well with cooling rates predicted by fission-track thermometry and Ar-40/Ar-39 ages. The OSM predicts an inverse correlation between the cooling rate and the petrographic type. Low correlations found between the MCRs and petrographic type indicate that chondrite parent asteroids were not assembled with onion shell structures.

Taylor, G. Jeffrey↗
NASA NTRS1987

Differential CCD photometry of faint asteroids in crowded star fields and nonphotometric sky conditions

It is demonstrated that the use of an imaging CCD detector array allows photometric observations of comparatively faint asteroids moving rapidly through a complex background of star images. The shortage of observing time is alleviated by taking advantage of the presence of comparison stars that are observed simultaneously on the CCD imaging area and at small angular separations from the asteroid. These reference stars allow the effects of thin cirrus clouds or haze to be compensated to a degree adequate for the acquisition of scientifically original data.

Wisniewski, W. Z.↗
NASA NTRS1987

Photometric geodesy of main-belt asteroids. I - Lightcurves of 26 large, rapid rotators

A 'photometric geodesy' program is selected on the basis of light-curve data from five years' observations of large, rapidly rotating asteroids, where the observing protocol was designed to obtain precise, absolute photometry at a wide variety of orbital longitudes and phase angles. A total of 257 complete or partial light-curves are obtained for 26 asteroids; the data set will allow the future determination of pole positions and shapes, as well as to constrain the geophysical traits of these bodies.

Weidenschilling, S. J.↗
NASA NTRS1987

Photoelectric lightcurves of the asteroid 1862 Apollo

A period of rotation of 3.0655 + or - 0.0008 hr is presently established for the 1862 Apollo asteroid on the basis of photoelectric light curves obtained during December 1980 and April-May 1982. The slope of the phase curve is typical for a moderate albedo asteroid. A pole position has been calculated using the observed deviation of the light curve from constant periodicity. While the formal uncertainty of the solution for the pole position is less than 10 deg, it may be several times that figure or even entirely wrong.

Harris, A. W.↗
NASA NTRS1987

Coordinated observations of asteroids 1219 Britta and 1972 Yi Xing

A coordinated observational program conducted for asteroids 1219 Britta and 1972 Yi Xing has yielded a sidereal rotation period of 5.57497 + or - 0.00013 h for the former, which has retrograde rotation and may be classified as an S-type asteroid on the basis of its spectra and albedo. The 1972 Yi Xing synodic period is found to be 14.183 + or - 0.003 h, with an observed light-curve amplitude amplitude of 0.18 mag; its five-color measurements also appear consistent with an S-type classification. A light-curve maximum absolute magnitude of 13.32 + or - 0.01 is also obtained.

Binzel, Richard P.↗