Icarus
We have developed a Monte Carlo model of the dynamical evolution of a binary asteroid crossing the Earth's orbit. At each close encounter with the Earth, the binary system undergoes impulsive variations of its orbital energy and angular momentum. Thus, after a great number of encounters, the system is dynamically evolved, and the two components may have either collided or escaped "to infinity...
Contrary to recent assertions in the literature, lunar emission spectra obtained at an altitude of 32 km with a balloon-borne telescope are virtually undistorted by atmospheric absorption, except in the ozone region. These spectra have been found to correlate closely with laboratory emission spectra of returned lunar samples measured in a simulated lunar environment. Thus, lunar spectra obtained with...
Ballistic transport in planetary rings is the net radial transport of mass and angular momentum due to exchanges of meteoroid impact ejecta between neighboring ring regions. The detailed linear stability analysis in this paper demonstrates that ballistic transport causes wavelike disturbances to grow and propagate in an otherwise uniform ring. The growth is strongest for intermediate values of the...
The U-B color has been suggested as a predictor of the presence of water of hydration on asteroids. Photometry from the Eight-Color Asteroid Survey was used to test this concept. An overlap in U-B colors prevents this magnitude difference from distinguishing between surface material that was thermally processed at higher temperatures and surface material that was aqueously altered. Two tests of the...
Observations of CO at 2.6 mm (115.27 GHz) were made with the OVRO millimeter interferometer in 1986 and 1988, yielding high-quality disk-resolved spectra which were inverted to determine the CO mixing ratio profile from distinct regions on the disk, allowing us to map the distribution of CO in the upper mesosphere of Venus both horizontally and vertically. The 1986 observations were of the morning...
The quantum yield and reaction threshold for the photochemical dissociation of cyanoacetylene into a hydrogen atom and the cyanoethynyl radical have been determined. The quantum yield at 185 nm is ∼0.09. The threshold is ∼240 nm. Combination of this data with literature values shows that production of excited-state cyanoacetylene is the major primary process resulting from irradiation between 185...
We report the results of a detailed experimental study of the kinetics and mechanism of pyrite (FeS 2 ) chemical weathering under Venus surface conditions. Pyrite is thermodynamically unstable on the surface of Venus and will spontaneously decompose to pyrrhotite (Fe 7 S 8 ) because the observed S 2 partial pressure in the lower atmosphere of Venus is lower than the...
In this paper we examine some realistic numerical integrations of objects in the 3/1 commensurability. We show that, as pointed out by the analytic model in Moons and Morbidelli (1995, Icarus, 114, 33-50), the dynamics in the 3/1 commensurability is strongly chaotic due to the overlapping of secular resonances. As a consequence, the eccentricity of bodies in the 3/1 commensurability can increase to...
Our recent rocket-borne observations have provided valuable information on the near-infrared feature of the zodiacal light at high ecliptic latitude and large solar elongation. The observed spectra at λ < 2.5 μm where the zodiacal light dominates the sky brightness are smooth without significant line features and much redder than the solar color. The observed color of the zodiacal light and the...
The atmospheric flow on Io is numerically computed in a flat 2-D axisymmetric geometry for a sublimation atmosphere on the trailing hemisphere subjected to plasma bombardment, UV heating, and IR cooling. Calculations are performed for subsolar vapor pressures of ∼6.5 × 10 3 Pa (∼3 × 10 18 SO 2 /cm 2 )and 6.8 × 10 -4 Pa (∼4 × 10 17 SO 2 /cm ...
Resonance lock, when a nonconservative force is present, may have a stable or an unstable character. We investigate which kinds of force yield stability and which yield instability, for any exterior resonance. We develop an analytical model, through which a criterion for stability is established. This criterion is checked by numerical integrations of the complete equations of motion with a conveniently...
We reanalyzed the CN images of Comet P/Halley, in which jets have been discovered for the first time, in search of shell structures. Shells were actually detected at the outer edges of the frames on those dates for which shells with radii small enough to be covered by the limited field of view of the CCD were predicted. The C 2 images of the same data set were subjected to an analogous investigation...
A search of Magellan synthetic aperture radar images covering ~98% of the venusian surface shows that aeolian features occur at all longitudes and latitudes. A global data base for wind streaks, the most common type of aeolian feature, was developed. For each of the 5970 streaks in the data base, information was compiled on location, streak type, radar backscatter, dimensions, azimuth, orientation...
Visible and near-infrared reflectance spectra (0.4-1.0 μm) of 21 Vesta-like asteroids and 12 HED meteorite powders (<25 μm in grain size) have been compared. Each reflectance spectrum was deconvolved into modified Gaussians and a constant background to allow comparisons of the 1-μm absorption band position and shape. The 1-μm band centers and widths of Vesta-like asteroids and HED meteorites generally...
The location of the secondary and secular resonances inside the three-dimensional 2:1 mean motion resonance with Jupiter is investigated both analytically and numerically. A bridge between the low-eccentric secondary-resonance belt and the high-eccentric secular-resonance complex is found and its mechanism analyzed. This bridge is the crucial link in the path taken by the orbit displayed by Wisdom...
Solar phase curves for Rhea are presented using new telescopic opposition data along with Voyager imaging observations. Two viable solutions were found to Hapke's model (1986, Icarus 67, 264-280) which was used to describe this phase curve. The porosity derived from the model's opposition parameters show that the optically active portion of Rhea's regolith has a porosity between 80 and 95%, which...
An axisymmetric cloud model with detailed microphysics was used to calculate the electrical development of a jovian water cloud. The charge separation mechanism was based on the noninductive interaction between ice crystals and graupel particles in the presence of supercooled liquid droplets. The results show that for plausible concentrations of cloud condensation and freezing nuclei in the atmosphere,...
Microwave observations of the Moon during the eclipse of November 28-29, 1993, are reported. Observations were made at 1.327 mm wavelength with a 12-m-aperture radio telescope. Points observed were at the lunar equator and 42 o north and south lunar latitude, all near the sub-Earth meridian of lunar longitude. Brightness temperature (T B ) was observed to decrease a maximum of 25%...
Carbonaceons chondrites commonly contain 10-20% water-soluble salts by mass, the products of low-temperature aqueous alteration under oxidizing conditions. About 75% (by mass) of chondrite salts typically consists of magnesium sulfate hydrates. Conditions similar to those that affected carbonaceous chondrites may have prevailed within some asteroids and icy satellites, resulting in the formation of...