Icarus
A dusty and moist martian atmospheric boundary layer model was augmented with a soil temperature diffusion scheme, simple soil hydrology, and interactive icecloud physics. It was applied to the summertime conditions at the Viking Lander 1 site (48 o W, 22.5 o N). A good simulation of the observed 1.6-m diurnal VL-1 temperature cycle was obtained when the soil properties were adjusted...
Based on computer simulations of the thermal behavior of chondrules and aggregates of dust as well as on existing observational and experimental evidence, we propose a model for the formation of chondrules by electromagnetic (EM) radiation. Heating occurred primarily by the absorption of ~0.3- to 8-μm EM radiation, with peak fluxes near ~5 x 10 6 W m - 2 and heating durations between...
The Apollo asteroid 4179 Toutatis passed within 0.0242 AU of Earth in December 1992, and photometry was obtained by observers from at least 25 sites around the world, at solar phase angles between 121 o and 0.2 o . The phase curve is well described in the H, G system with a mean H of 15.3 and a slope parameter G of 0.10 +/- 0.10. However, the rotational lightcurve is very unusual....
We study the trajectories of planetesimals whose orbits decay starward as a result of gas drag and are perturbed by the gravity of a massive planet on an eccentric orbit. Each planetesimal ultimately suffers one of three possible fates: (1) trapping in a mean motion resonance with the planet, (2) accretion by the planet, or (3) passage by the planet and continued orbital decay.At moderate to large...
Because of its large cross section, Saturn's rings have very strong collisional interaction with the interplanetary meteoroids. The continuous process of impact fragmentation and erosion is a major mechanism driving the mass and angular momentum transport of the ring system with a dynamical time scale estimated to be as short as 10-100 million years. An assessment of the impact ejecta production rate...
The 183.310-GHz water vapor transition has been observed in the Venus atmosphere for the first time. The detection was made in January 1991, using the 30-m IRAM radiotelescope. A spectrum of Saturn, recorded during the same night, was used to remove the contribution due to terrestrial mesospheric water. Using the depth and the FWHM of the observed absorption line, we derive a water mixing ratio of...
We study by numerical integration the secular dynamical behavior of a sample of 32 Mars-crossing and near-Earth asteroids. We divide the planet-crossing asteroid population into two groups, with semimajor axis a >2 AU and <2 AU. In the former region (a>2 AU), a computer-assisted analytical theory allows us to select 24 objects which are inside or close to the main secular resonances. The...
Spectroscopic analyses have shown that smectites enhanced in the laboratory with additional ferric species exhibit important similarities to those of the soils on Mars. Ferrihydrite in these chemically treated smectites has features in the visible to near-infrared region that resemble the energies and band strengths of features in reflectance spectra observed for several bright regions on Mars. New...
In the framework of our project for the establishment of a follow-up station to be integrated into the future European network for the search for near-Earth objects (EUNEASO), we have carried out photometry and astrometry of eight near-Earth asteroids and two Mars crossers. From a total of 42 single-night lightcurves we have determined for the first time accurate rotation periods and amplitudes for...
The effects of collective particle behavior on the trapping strength of a perturber's mth order outer Lindblad resonance in a planetesimal disk are examined. We find that if the particle disk supports density waves, the spiral disk potential generated in response to forcing by the perturber shields particles from the perturber and may greatly diminish the perturber's ability to trap particles undergoing...
Voyager 2 images have been used to measure the instantaneous rotation state of Hyperion during the period of the spacecraft's 1981 flyby of Saturn, to define the satellite's shape, and to map geological features. For the 38 hr of image coverage at resolutions better than 17 km/pixel, control point calculations yield a rotation rate of 72 o /day, with a pole direction of RA = 226 +/- 4 ...
Many asteroids show absorption features diagnostic of hydrated minerals in the 3-μm region of the spectrum. Reflectance studies in this region can determine the hydration state of surface minerals and, by inference, the thermal histories of bodies. We have made spectrophotometric observations of eight E-class, M-class, X-class, and P-class asteroids in December 1991 and eight E-class and M-class asteroids...
Spatially resolved photometric observations of Phobos in nine narrow bands in the spectral range 315-600 nm were obtained by means of the KRFM instrument on board the Phobos spacecraft on 25 March 1989. There were initial difficulties with the interpretation of the data. However, some realistic solutions to these difficulties have been found, and now we present a revised version of the results that...
The atmospheric circulation of Titan is investigated with a general circulation model. The representation of the large-scale dynamics is based on a grid point model developed and used at Laboratoire de Meteorologie Dynamique for climate studies. The code also includes an accurate representation of radiative heating and cooling by molecular gases and haze as well as a parametrization of the vertical...
Artemis Chasma, an ~2600-km-diameter arcuate trough located in southwestern Aphrodite Terra, Venus, has been the site of <250 km of regionally coherent, southeast-directed, lithospheric convergence and strike-slip displacement. This study examines the tectonics of the interior platform encircled by Artemis, the annulus of deformation coinciding with the trench, and the exterior region. A prominent...
We present the results of photometric observations of 12 asteroids, performed from 1985 through 1989 at the Astronomical Observatory of Teramo (Italy), Astronomical Observatory of Turin (Italy), and European Southern Observatory (ESO, La Silla, Chile). Using the EA pole determination method described in G. De Angelis (Planet. Space Sci., 41, 285-290, 1993), we have obtained the first spin and shape...
A number of one- and two-layer atmospheric models have been applied to the study of Jupiter's tropospheric circulations over the past two decades in an effort to characterize the basic-state properties of the zonal winds and to study the influence these winds have on the dynamics of long-lived vortices like the Great Red Spot. By singling out the basic state that corresponds to neutral stability with...