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Fine grained particles <50 μm in size dominate particle size distributions of many planetary surfaces. Despite the predominance of fine particles in planetary regoliths, there have been few investigations of the systematic effects of the finest particles on reflectance spectra, and on the ability of quantitative models to extract compositional and/or textural information from remote observations...
Solar occultation spectrometry of the martian atmosphere was performed during the Phobos mission with the Auguste experiment in the UV, visible, and NIR spectral ranges. The entire domain of data in the range of 1.9 μm has been reanalyzed to retrieve all available information about the water vapor vertical profile. Accurate consideration of the instrumental corrections and a probabilistic concept...
We have numerically integrated approximately 500 systems of mutually gravitating bodies which were based on subsets of the uranian satellite system. In each run within a set, the satellite masses were initially multiplied by a common mass enhancement factorm f . The simulations were terminated at the ''crossing time,''t c , when mutual perturbations excited eccentricities sufficiently...
Several recent studies have noted that the orbital evolution of many comets is influenced by mean-motion resonances with Jupiter. However, the distribution and relative importance of these resonances and the orbital characteristics of the comets affected have not been addressed to date. Here I show analytically that cometary orbits with periods greater than a critical value,P c , (which depends...
We present a detailed study of the S I triplet emissions near 1814 A in a variety of comets. Even in a moderately dense cometary coma the ground-state component (1807 A) of the triplet turns out to be more or less optically deep. Therefore, any straightforward interpretation of the measured S I flux in terms of agfactor and a column density is incorrect. We combine a Monte Carlo radiative transfer...
We predict the OH column that will be present in the polar regions of the mercurian exosphere for physically realistic ice deposits at the poles, including both surface and buried ice. The probable rates of accretion by meteoritic, asteroidal, and cometary sources are computed and compared with loss rates. The rate of accretion of water at the poles from the nominal meteoritic infall is 2.5-8 x 10...
We model the collisional evolution of Trojan asteroids using a numerical code which combines recent calculations of the intrinsic collision probabilities and impact speeds in the Trojan swarms (Marzariet al.1996) with our current understanding of the outcomes of high-velocity collisions between asteroid-sized bodies. Using plausible collision parameters and energy scaling of impact strength with size,...
Minor planet 1993SC, with a semi-major axis of 39.67 AU, is one of the brightest of numerous recently discovered objects with orbits close to or beyond Neptune. It is a member of the Kuiper Belt, a planetesimal population remaining from the formation of the Solar System. We present optical photometry which indicates a lightcurve amplitude of less than 0.2 magnitude for 1993SC and which does not support...
High temperature chemistry in the fireballs created by the impacts of Comet P/Shoemaker-Levy 9 in Jupiter has been studied using thermochemical models of the impacts. Explosions of the fragments at different levels in the jovian atmosphere ranging from above the clouds of NH 3(s) to below the clouds of H 2 O (s) have been considered. The chemical composition...
The Edgeworth-Kuiper Belt contains a population of objects ~10 3 times that of the main asteroid belt, spread over a volume ~10 3 larger and with relative speeds ~10 times lower. As for the asteroids, the size distribution of Edgeworth-Kuiper Belt objects has been modified by mutual impacts over Solar System history. We have modeled this collisional evolution process using a numerical...
We present high-resolution 8-14 μm observations of Shoemaker-Levy 9 sites conducted on July 20, 30, and 31 1994 UT at the NASA Infrared Telescope Facility. Stratospheric heating was detected from strong enhancements of methane emission near 8.1 μm over areas at least 15,000 km wide around the K site observed 23 hr after impact and around the L site 11 hr after impact. The intensity distribution between...
For the first time the role of the internal heat source, due to radioactive decay in Triton's core, is investigated with respect to geyser-like plumes. Triton is one of only three known objects in the Solar System (the other two are Earth and the jovian satellite Io) where eruptive activity has been definitely observed. A new mechanism of energy supply to the Tritonian eruptive plumes is proposed...
We present the results of experiments performed by keV ion (He and H) bombardment of frozen mixtures of H 2 O:CO 2 and of pure CO 2 ice. Using keV He ions we confirm the already reported measurement of carbonic acid (H 2 CO 3 ) production in an ice mixture of frozen water and carbon dioxide (1:1) after irradiation by 0.7 MeV H ions (Moore, M. H., and R. K. Khanna...
Conventional techniques for investigation of crater populations make use of size-frequency distributions, but typically disregard the statistical properties of the spatial distribution of craters. Cratering of a surface is generally a spatially random process, so the distributions of craters on lightly cratered surfaces can be expected to be random. As crater obliteration becomes important, however,...
Most asteroids are characterized by positive Lyapounov Characteristic Exponents (LCE), which means that their orbits are chaotic. Indeed, the striking fact is that for many of them the maximum LCE is very large, with a corresponding Lyapounov time shorter (often much shorter) than 100,000 years, as we report in this work. This finding is in apparent contradiction with the overall orbital stability...
Numerical results of impact of Comet Shoemaker–Levy 9 (SL9) on Jupiter are compared with observational phenomena to investigate the size and origin of SL9 and impact features. Plume evolution is simulated numerically for 0.4- and 2.0-km-diameter (D) impactors. Analytical estimates indicate that the maximum plume heights are proportional to (D/lnD) 3 . This relation is also confirmed by the...
We present high–resolution 11–μm NH 3 observations of the Shoemaker–Levy 9 sites that were conducted on May 15–18, 1995 UT at the NASA Infrared Telescope Facility. No emission from stratospheric NH 3 was detected at any location. The upper limit on the NH 3 column density above 40 mbar is 6 × 10 15 molecule cm −2 , about 30 times less than that observed on July...
The lightcurves and derived production rates of volatiles such as water for short-period comets show asymmetries around perihelion. These asymmetries do not follow a specific trend, and short-period comets are as likely to be brighter preperihelion as postperihelion. This and images of the nucleus of Comet P/Halley suggest that the activity of comet nuclei is driven by a small number of active regions...
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