Icarus
Data from eight stellar occultations by Neptune between 1984 and 1988 are analyzed to set limits on the optical depths of the continuous Adams and Le Verrier Rings, and to search for previously unidentified occultations by the arcs in the Adams Ring. We employ the approach introduced by Sicardy et al. (1991), Icarus 89, 220-243) and convert the raw lightcurves to radial profiles of equivalent width...
The most concentrated deposits of SO 2 frost on Io occur within a series of large equatorial basins. About 30% of the surface is covered by SO 2 outside of the basins, increasing to more than 50% within the basins. This pattern is poorly expressed in the region from longitude 240 o to 360 o where bright areas are frequently buried by the fallout from the large Pele-type...
Impact experiments, cratering and fragmentation, on water ice were performed in order to test the scaling laws previously constructed on rocks and sands for studying the collision process in the planetary history. The installation of a vertical gas gun in a cold room at -18 o C (255 K) made it possible to use a projectile of water ice and to get the detailed mass distribution of ice fragments...
We use a new indirect imaging method, matrix lightcurve inversion (MLI), to generate surface albedo maps of Pluto from the rotational photometric lightcurves. The mathematical basis of MLI is established and a constrained iterative regularization method used to invert the underdetermined system of equations. If the secular dimming of Pluto observed in all phases of the rotational lightcurves from...
During the 1981 Voyager encounter, Titan's stratosphere exhibited a large thermal asymmetry, with high northern latitudes being colder than comparable southern latitudes. Given the short radiative time constant, this asymmetry would not be expected at the season of the Voyager observations (spring equinox), if the infrared and solar opacity sources were distributed symmetrically. We have investigated...
We present CCD spectra (0.54-0.98 μm) as a function of rotational phase of the Clementine target 1620 Geographos. We confirm the asteroid's S-type taxonomic classification (more precisely, SII-SIII). The surface mineral assemblage appears to be a metal and pyroxene/olivine mixture. Though our spectral observations sampled the rotational lightcurve well, we were unable to detect significant color variations...
We have studied the orbital evolution of micrometer-sized asteroidal dust particles under the influence of planetary gravitational perturbations, radiation pressure, Poynting-Robertson (PR) drag, and solar wind drag. It is found that a significant fraction of the 2-μm diameter particles, with β = 0.26, are thrown into the 1:1 mean motion resonance zone with Jupiter when they are released from their...
We obtained four images of the asteroid 4179 Toutatis during its close approach to the Earth on 10 December 1992 with the planetary camera of the Hubble Space Telescope. The distance between the Earth and Toutatis at the time of our observations was 0.0291 AU (4.35 x 10 6 km); a single planetary camera pixel width subtends a distance of 926 meters at this distance. The solar phase angle was...
A new distribution of phosphorus compounds in the atmosphere of Jupiter is given, using revised values for the chemical constants. In contrast with previous works, it is shown that phosphine PH 3 remains the most abundant equilibrium gaseous compound even at the upper levels of Jupiter's troposphere. The observed PH 3 abundance is equal to the equilibrium value, at all temperatures...
We have inverted high-phase-angle Voyager images of Neptune to determine the atmospheric extinction coefficient as a function of altitude and the scattering phase function at a reference altitude. Comparisons between theoretical models and observations help separate the contributions from molecular Rayleigh and aerosol scattering and help determine the variation of the aerosol size, concentration,...
We present the results of a spectral survey of S-, K-, Q-, and M-type asteroids in seven colors in the infrared (0.9 to 2.3 μm) conducted at the Infrared Telescope Facility on Mauna Kea from 1992-1994. This asteroid spectral collection consists of a total of 126 observed objects. Among them are 96 S-types, 17 M-types, 1 Q-type, 1 C-type, 4 previously reported K-types, and possibly 7 newly identified...
The semianalytical theory of downslope windstorms, originally developed to understand large increases in surface winds in the lee of major mountain chains on Earth, such as the famous windstorms in Boulder, Colorado, is applied to martian conditions. The focus of this work is to assess whether this theory can help us understand dark erosional wind streaks downstream of ridges on the martian surface...
Traditional accretion simulations predict rapid accumulation of ring debris into single satellites, while most theories of ring formation dismiss any accretion within the classical Roche limit. The former contradicts the continued presence of planetary rings, while the latter fails to adequately account for the many small satellites observed within ring systems. The coexistence of rings and small...
We reexamine the inviscid solar-wind equations with heat conduction from below and establish a fundamentally new approach for finding supersonic solutions. Although the problem is fourth order, only two independent integration constants can be arbitrarily assigned, since two boundary conditions that are required to specify well-behaved supersonic solutions determine the values of the other two constants...
The role of irradiation of carbon-bearing grains by energetic particles in formation and evolution of organic matter in the interstellar medium and Solar System is studied. Experimental evidence for the possibility of the organic synthesis directly from inorganic reactants by keV ion bombardment is presented. Irradiation of graphite powder containing hydrogen by He + and N + as well...
The uranian system exhibits contradictory characteristics; the rotational axis of Uranus is inclined by about 98° from the axis of its orbital angular momentum and the orbits of five major satellites of Uranus are remarkably regular, namely, the eccentricities are very small and the orbital planes almost coincide with the equatorial plane of Uranus.In the present study, we investigated the tidal evolution...
The spatial distribution of different types of rampart craters on Mars suggests a hemispheric asymmetry in the distribution of ground ice. The northern plains, especially major topographic depressions near the terminations of outflow channels, have high percentages of rampart craters. Two of these basins, Acidalia and Utopia Planitiae, received extraordinarily large amounts of water and sediment from...