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Using the Moon to occult the Sun, the Clementine spacecraft used its navigation cameras to map the inner zodiacal light at optical wavelengths over elongations of 3 ε 30 o from the Sun. This surface brightness map is then used to infer the spatial distribution of interplanetary dust over heliocentric distances of about 10 solar radii to the orbit of Venus. The averaged ecliptic surface brightness...
The analysis of radar observations of the asteroid 4179 Toutatis by Hudson and Ostro (1995, Science270, 84-86) yielded a complex spin state. We revisit the visible lightcurve data on Toutatis (Spencer et al. 1995, Icarus117, 71-89) to explore the feasibility of using a rotational lightcurve to recover the signature of an excited spin state. For this, we apply Fourier transform and CLEAN algorithm...
An explanation of the dynamical mechanism for apse alignment of the eccentric uranian rings is necessary before observations can be used to determine properties such as ring masses, particle sizes, and elasticities. The leading model (P. Goldreich and S. Tremaine 1979, Astron J.84, 1638-1641) relies on the ring self-gravity to accomplish this task, yet it yields equilibrium masses which are not in...
We show that the ''snowline'' altitude on Titan, above which the condensed nonideal methane-nitrogen phase is solid, is lower (~14 km) near the equator than at high latitudes (~19 km). This counterintuitive result derives from the thermodynamic behavior of the binary condensate. The snowline altitude is an operating constraint on future Titan missions where icing would pose a ceiling on atmospheric...
Irregular satellites-moons that occupy large orbits of significant eccentricity e and/or inclination I-circle each of the giant planets. The irregulars often extend close to the orbital stability limit, about 1/3-1/2 of the way to the edge of their planet's Hill sphere. The distant, elongated, and inclined orbits suggest capture, which presumably would give a random distribution of inclinations. Yet,...
In a recent Icarus article, Shkuratov and Bondarenko (2001) propose a model for the depth of the lunar regolith based on 70-cm radar observations and near-infrared spectroscopy. This model treats the regolith as a single homogeneous layer of lossy dust, and ignores scattering by buried rocks. There is also an implicit assumption that the regolith substrate is everywhere of uniform morphology. Radar...
A recently published model of the Near Earth Object (NEO) orbital-magnitude distribution (Bottke et al., 2002, Icarus156, 399-433.) relies on five intermediate sources for the NEO population: the ν 6 resonance, the 3:1 resonance, the outer portion of the main belt (i.e., 2.8-3.5 AU), the Mars-crossing population adjacent to the main belt, and the Jupiter family comet population. The model...
A multi-wavelength radio frequency observation of Venus was performed on April 5, 1996, with the Very Large Array to investigate potential variations in the vertical and horizontal distribution of temperature and the sulfur compounds sulfur dioxide (SO 2 ) and sulfuric acid vapor (H 2 SO 4 (g)) in the atmosphere of the planet. Brightness temperature maps were produced which...
We present numerical simulations of the thermal and dynamical histories of solid particles (chondrules and their precursors-treated as 1-mm silicate spheres) during passage of an adiabatic shock wave through a particle-gas suspension in a minimum-mass solar nebula. The steady-state equations of energy, momentum, and mass conservation are derived and integrated for both solids and gas under a variety...
Impact strength and cratering ejecta were studied for porous targets of pure ice and icy-silicate mixture in order to clarify the accumulation and destruction (shattering) condition of small icy bodies. The icy projectile impacted on the cylindrical targets with the porosity up to 55% at a velocity of 150 to 670 m/s at -10 o C. The porosity dependence of the impact strength and that of the...
The recent discovery of a relatively small basaltic asteroid in the outer main belt with no apparent link to (4) Vesta raised several hypotheses on its origin. We present the results of a dynamical and mineralogical study of the region near (1459) Magnya intended to establish its origin. The dynamical analysis shows that the region is filled with high-order two-body and three-body mean motion resonances...
The tremendous heating dissipated by jovian tides in Io's interior is essentially evacuated by an intense volcanic activity so that the heat is removed from the interior to the surface, much more by advection than by conduction through the lithosphere. The efficiency of this heat pipe cooling process is investigated through numerical models of convection performed in spherical geometry with a permeable...
Galileo Probe Atmospheric Structure Investigation (ASI) pressure and temperature sensor data acquired during the parachute descent phase have been used to derive the static stability structure of Jupiter's troposphere at pressure levels of 0.5-22 bars using three techniques. The first approach utilizes both the p-sensor and T-sensor data, but since the p-sensor's zero offset was significantly affected...
Lightcurve observations of 16 near-Earth objects (NEOs) and 2 Mars-crossers in 1996-1999 from three observational sites are presented. Eight objects were observed shortly after their discovery within the follow-up program of NEO observations. We were able to determine rotation periods for 14 asteroids. For 8 objects (5626, 5732, 1998 FM5, 1998 FX2, 1998 UT18, 1998 VO33, 1999 RQ36, 1999 US3) our determinations...
Linear wave patterns in Jupiter's clouds with wavelengths strongly clustered around 300 km are commonly observed in the planet's equatorial atmosphere (F. M. Flasar and P. J. Gierasch, 1986, J. Atmos. Sci.43, 2683-2707). We propose that the preferred wavelength is related to the thickness of an unstable shear layer within the clouds (A. P. Ingersoll and D. W. Koerner 1989, Bull. Am. Astron. Soc.21,...
We report Doppler-only (cw) radar observations of basaltic near-Earth asteroid 3908 Nyx obtained at Arecibo and Goldstone in September and October of 1988. The circular polarization ratio of 0.75+/-0.03 exceeds ~90% of those reported among radar-detected near-Earth asteroids and it implies an extremely rough near-surface at centimeter-to-decimeter spatial scales. Echo power spectra over narrow longitudinal...
We present coupled chemical-microphysical models for the formation, growth, and physical properties of the jovian polar haze based on a gas-phase photochemical model for the auroral regions developed by A. S. Wong et al. (2000, Astrophys. J.534, L215-217). In this model, auroral particle precipitation provides an important energy source for enhanced decomposition of methane and production of benzene...
The influence of Saturn's gravitational tide on the atmosphere of Titan is investigated by means of a three-dimensional general circulation model. Titan's orbital eccentricity of 0.0292 gives rise to time-dependent radial and librational tide whose potential circles eastward on Titan. Unlike atmospheric tides on terrestrial planets, Saturn's tide on Titan has a large impact on the dynamic meteorology...
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