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At least 973 records · Page 54
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

The motions of satellites and asteroids - Natural probes of Jovian gravity

Before the recent Pioneer probes, our knowledge of Jupiter's gravitational field was obtained from the motions of satellites and asteroids. The study of orbital perturbations of asteroids near the 2:1 commensurability yielded a value of the mass of the Jupiter system at least as precise as that obtained by the artificial probes. Precession of the inner satellites' orbits placed constraints on the harmonic coefficients J2 and J4. A correction to the satellite determination of J4 lowers its mean value closer to the Pioneer result. The orbital grouping among the outer satellites and the resonance among the Galilean satellites are described in detail, but the origins of these phenomena are not understood. However, recent research suggests that the explanation will be intimately associated with models of the origin and evolution of the planet itself.

Greenberg, R. J.↗
NASA NTRS1976

A note on the cosmogony of the asteroidal belt

Several arguments based on the orbital dynamics of the asteroids are used to support the idea that the original solar nebula might not necessarily be the Laplacian type of thin disk-like structure. The orbital distribution of the large asteroids is suggested to be a direct result of their accretions of condensed grains in eccentric orbits via the jet stream process.

Ip, W.-H.↗
NASA NTRS1977

Round-trip mission requirements for Asteroids 1976 AA and 1973 EC

The feasibility of manned or unmanned missions to two recently discovered asteroids is assessed. Characteristics of a likely target for a round-trip exploratory excursion include: a period close to one year; and an orbit that is nearly circular and nearly coplanar with the ecliptic. Mass requirements and optimal times of launch are investigated for unmanned and manned missions to Asteroids 1976 AA and 1973 EC (recently numbered 1943); 365-day round-trip trajectories in the first half of the 1990s are proposed. However, since neither of the two targets considered entirely fulfills all the necessary orbital characteristics, neither can offer the opportunity for a fast low-energy round-trip mission; nevertheless, other minor planets crossing earth's orbit may be found to meet the requirements.

Niehoff, J. C.↗
NASA NTRS1978

Asteroids: An Exploration Assessment

The current state of asteroid science is assessed. Future space missions to gain more knowledge on asteroid relationship to solar system formation are outlined.

Morrison, D.↗
NASA NTRS1978

Physical observations and taxonomy of asteroids

Physical asteroid observations are summarized and the classification scheme to describe asteroid surfaces in relation to mineralogical composition is detailed. The principle classes, distinguished on the basis of a number of parameters involving albedo and color, are called C, S, and M.

Morrison, D.↗
NASA NTRS1978

Earth-approaching asteroids: Populations, origin, and compositional types

Origin, physical properties, and discovery history of smaller asteroids are reviewed. They appear to link the main belt objects, namely the comets and meteorites. Physical observations suggest that a wide variety of compositional types are represented among the near-earth asteroids; the apparent rarity of carbonaceous objects is stated.

Shoemaker, E. M.↗
NASA NTRS1978

Some important imaging goals for asteroid missions

Very high resolution imaging provides the best means of examining geological processes acting on asteroid surfaces. Imaging also may be important for revealing how asteroids accreted and for obtaining some data on their differentiation history. Imaging from rendezvous together with Doppler tracking is the only way to determine accurate densities and hence place limits on bulk composition.

Veverka, J.↗
NASA NTRS1977

Search for correlation between asteroid families and classes

A correlation between membership in a dynamically defined asteroid family and membership in a given asteroid spectral class is sought. Examination of 10 families each with five or more classified members indicates a correlation for the 4 families whose existence is best established, and no correlation for the remaining 6 families. This conclusion supports the break-up hypothesis for the origin of some families, while not contradicting that hypothesis for any family.

Hansen, O.↗
NASA NTRS1977

On the orbital dependence of the asteroidal collision process

Collision of asteroids with the main-belt asteroid population is considered with the effect of the impact kinetic energy taken into account. It is found that objects in eccentric orbits have a larger probability of destructive collision as compared to objects in orbits with mean values of eccentricity (equal to 0.15) and inclination (equal to 10 deg); also orbits with small semimajor axes (about 2.3 AU) are found to have peak values of the probability of destructive collision.

Ip, W.-H.↗
NASA NTRS1977

The E asteroids and the origin of the enstatite achondrites

Color, polarization, and albedo data are summarized for the three known minor planets of optical type E: 44 Nysa, 64 Angelina, and 434 Hungaria. The inventory of E asteroids with dimensions in excess of 50 km is shown to be essentially complete. The surfaces of the E objects evidently consist of colorless translucent iron-free silicates such as plagioclase, forsterite, or enstatite. Their possible identification as the source of enstatite achondrites is consistent with laboratory polarimetry of the Norton County aubrite. Both Nysa and Hungaria seem to be rather favorably situated for the production of meteorites. Nysa has a highly aspherical shape and is dynamically associated with the metal-rich asteroid 135 Hertha and several small objects also apparently of the metal-depleted E type. The configuration is suggestive of the fragments of a differentiated parent body, in which Hertha originated as the iron core and Nysa as the largest surviving mantle fragment. The relative volumes, however, are not consistent with simple igneous differentiation from a chondritic composition.

Zellner, B.↗
NASA NTRS1977

On the prograde rotation of asteroids

Sets of diameter determinations before and after opposition for the asteroids Ceres, Pallas, Vesta, and Fortuna have been studied statistically for indications of spin direction. All four asteroids are tentatively found to have prograde spin. For Ceres, that conclusion is virtually certain.

Hansen, O.↗
NASA NTRS1978

Asteroid 1 Ceres - Evidence for water of hydration

An absorption feature centred near 3.0 microns has been discovered in the infrared spectrum of asteroid 1 Ceres. This spectrum has been compared with laboratory spectra of meteorites and shows great similarity to the spectra of type II carbonaceous chondrites. By analogy this suggests the presence of about 10-15 per cent water in the form of water of hydration on the surface of Ceres. This is the first evidence of water in the surface material of an asteroid.

Lebofsky, L. A.↗
NASA NTRS1977

Ion Drive multi-asteroid rendezvous trajectories

The general characteristics of multiasteroid rendezvous missions are examined, taking into account a use of an improved solar electric propulsion system, called Ion Drive. The improvements are related to the development of light-weight solar cells, extensions to high thruster power levels with high exhaust velocity, and the attachment of solar concentrators to increase the power available beyond 1.5 AU. Flight times on the order of 500-800 days are generally required. It is assumed that a stay time of about 60 days at each asteroid is adequate. Attention is given to launch and spacecraft parameters, the search technique, and multiasteroid tours involving Ceres and Vesta. It is found that at least four asteroids in the main belt, generally selected from those with known characteristics, may be reached on a single mission with a 100-kg separable probe landed on each one.

Bender, D. F.↗
NASA NTRS1978

Model consideration of the bombardment event of the asteroidal belt by the planetesimals scattered from the Jupiter zone

The temporal evolutions of the planetesimals scattered from the Jupiter zone for different masses of the proto-Jupiter (2 = 0.1 and b = 1.0 of the present mass) are investigated. Due to the combined effects of the orbital evolution of the planetesimals and the elimination of these projectiles either via impact capture or injection into escape velocity by the outer planets, the whole scattering process lasts about 100 million yr for case (a) and about 10 million yr for case (b). The longer time scale may be a good estimate for the accretion time interval of Jupiter while the shorter one gives the upper time limit of the late heavy-bombardment epoch of the terrestrial planets due to planetesimals scattered from the Jupiter zone. Consideration of the collisional interaction of these projectiles with the asteroids indicates that the corresponding bombardment effect could be rather appreciable. From this point of view, the structure of the asteroidal belt could be affected significantly not only by Jupiter's gravitational perturbation effect but also by its early scattering process.

Ip, W.-H.↗
NASA NTRS1978

Minor planets and related objects. XXV - UBV photometry of 145 faint asteroids

Magnitudes and colors on the UBV system are presented for 145 minor planets, including 31 objects in the Eos family, 14 in the Koronis family, 6 in the Nysa family, 11 in the Themis family, 4 Hungarias, 7 Hildas, 8 Trojans, and several objects in unusual orbits. Clearly defined color groups for the Eos, Koronis, Nysa, and Themis family members are strongly suggestive of origin from discrete parent bodies. The Nysas apparently show large light-curve amplitudes. The Mars-orbit crossers 1977RA and 1980 = 1950LA, the earth-orbit crosser 1976UA, and several main-belt asteroids are found to show peculiar colors of unknown significance. The Mars-orbit crosser 1916 = 1953RA appears to be a typical S object, while 1474 Beira and 1977VA show neutral colors. Asteroids at semimajor axis in excess of 4 AU (Trojans preceding and following Jupiter, 279 Thule, and 944 Hidalgo) all belong to a color group centered at B-V = 0.72, U-B = 0.24.

Degewij, J.↗
NASA NTRS1977

Soil maturity and planetary regoliths - The Moon, Mercury, and the asteroids

Observations of the Moon, Mercury and the asteroids provide data which can be used to assess current ideas about the optical maturation of regoliths of bodies without atmospheres. Telescopic data show Mercury's surface to be as optically mature as the Moon's while the asteroids appear to have 'fresh' surfaces. We suggest that these cases illustrate two different paths of regolith evolution caused by differing micrometeoroid impact velocities, gravity, and in some cases composition.

Matson, D. L.↗
NASA NTRS1978

1580 Betulia - An unusual asteroid with an extraordinary lightcurve

Results of UBV photometry and polarimetry of 1580 Betulia during its 1976 apparition are presented. The synodic period of rotation is found to be 6.130 hr. The linear phase coefficient and absolute magnitude of the primary maximum in V are 0.032 mag/deg and 14.88, respectively. No color variations with rotation or solar phase angle were detected, the mean colors being B-V = 0.66 and U-B = 0.24. Betulia's light curve is unique among asteroids studied to date in that it displays three maxima and three minima within one rotational cycle, indicative of a region of greater roughness and/or a dark spot on one of its broad faces. Polarization results indicate a low albedo and a mean diameter of about 7 km, establishing Betulia as the first C-type asteroid to be found among the Mars crossers. A model accounting for most features of Betulia's light curve is given by a prolate spheroid rotating about one of its shorter axes having an axis ratio of 1:1.21 with a major topographic feature on one of its broad faces.

Tedesco, E.↗
NASA NTRS1978

Characteristics of the cratering process on small satellites and asteroids

Photographs of the two known natural satellites of Mars - Phobos and Deimos - illustrate the importance of impact cratering in the postformational histories of the two moons and, by inference, the asteroids and other small planetary satellites. The objectives of the present study are to investigate qualitatively the impact cratering process on small bodies, to apply some of these considerations to the observed surfaces of Phobos and Deimos, and to consider the asteroids briefly in the light of these results. The cratering process on small bodies is discussed in three stages: compression, excavation, and modification. Nonescaping and escaping ejecta are considered.

Cintala, M. J.↗