The Infona portal uses cookies, i.e. strings of text saved by a browser on the user's device. The portal can access those files and use them to remember the user's data, such as their chosen settings (screen view, interface language, etc.), or their login data. By using the Infona portal the user accepts automatic saving and using this information for portal operation purposes. More information on the subject can be found in the Privacy Policy and Terms of Service. By closing this window the user confirms that they have read the information on cookie usage, and they accept the privacy policy and the way cookies are used by the portal. You can change the cookie settings in your browser.
We extract information from the failure of small objects to cause detectable damage to Pioneer 10, which has been inside the Kuiper Belt for a decade. Belt objects too small for telescope detection and too large for IR emission visibility are addressed. This is a size range with few other potential techniques, short of a new space mission, for direct detection. Results, based on an 8-inch radius propellant...
We investigate the growth and the orbital evolution of protoplanets embedded in a swarm of planetesimals using three-dimensionalN-body simulations. We find that among protoplanets, larger ones grow more slowly than smaller ones, while the growth of protoplanets is still faster than that of planetesimals. As a result, in the stage after rapid runaway growth, protoplanets with the same order mass grow...
Altimetric profiles from the Clementine LIDAR are used to calculate the depths of 29 large craters and basins on the Moon. Plotting the depths of the best preserved structures together with values for simple and complex craters measured in pre-Clementine studies reveals an inflection in the depth/diameter (d/D) curve in addition to the one revealed by pre-Clementine data. This inflection occurs in...
Ejecta features on the martian satellites are compared to models of ballistic emplacement and downslope motion. The asymmetric distribution of ejecta around the large crater Stickney on Phobos appears most easily explained if the crater were formed when Phobos was only slightly farther from Mars than at present (due to tidal evolution), where rotational and tidal effects allow spreading of low velocity...
The Eos family detected by Hirayama in 1918 has been always considered to be compositionally homogeneous. To investigate the composition and the homogeneity of the members of this family, we started a spectroscopic survey at the European Southern Observatory (ESO) with wavelength coverage ranging from 4800 to 9200 Å. We observed 45 Eos asteroid members, which constitutes the first large survey of...
Spectrophotometric data for the 0.338- to 0.762-μm region on the main-belt M-asteroids 75 Eurydike and 201 Penelope at small phase angles have been obtained. The spectral observations of 201 Penelope were accompanied by photometric observations allowing an assessment of geometric albedo variation of Penelope with rotation. The reflectance spectra of the bodies are shown to have both similar and differing...
We use new analysis techniques to constrain the shape of 433 Eros with Goldstone radar data obtained during the asteroid's close approach in 1975. A previous analysis of these data (Ostro, Rosema, and Jurgens, 1990,Icarus84,334–351) used estimates of the echo's spectral edge frequencies as a function of asteroid rotation phase to constrain the convex envelope of Eros' pole-on silhouette. Our approach...
We have refined a method to derive from Io's sodium cloud spectra precise estimates of the production rate and of the ejection velocity distribution at the exobase. This method is based on a detailed comparison between the observed spectra and synthetic spectra numerically simulated with a model derived from the Smyth and Combi (1988,Astrophys. J. Suppl.66, 397–411) formalism. The innovative aspect...
The Magellan radar imager detected approximately 60 dark (i.e., low backscatter cross section) parabola-shaped features on the surface of Venus; each parabola is oriented with the open end toward the west and envelops an impact crater near its “focus.” In this paper, we use a model of parabola formation to fit the 58 venusian parabolas observed to date, as well as 9 circular features that are similar...
We present angular scattering measurements of a suite of particulate materials of varying particle sizes and albedos over phase angles of 1 < Θ < 70°. Our results provide strong support for the hypothesis that coherent backscattering can be an important contributor to the enhanced reflectance seen in planetary regolith materials when observed at small phase angles, commonly known in the planetary...
The composition, size, and number of the most refractory grains to condense in Shoemaker–Levy 9 fireballs are discussed. Chemical heterogeneity in the fireball may have led to the formation of two principal types of refractory particles. Small particles consisting of a mixture of Al 2 O 3 and silicates are expected to form in those portions of the fireball where C/O < 1. In carbon-rich...
Amorphous magnesium silicate smokes were prepared by vapor phase condensation and annealed in vacuum. The samples were monitored by IR spectroscopy as a function of annealing time and temperature, focusing on the development of the 10 μm silicate feature. The IR spectrum of the initial condensate displayed a broad band at 9.3 μm. After annealing for 10.5 h at 1027 K, a dual maximum was established...
The Saturn ring plane crossings in 1995–1996 allowed observers using the Hubble Space Telescope and the W. M. Keck telescope to image the planet's diffuse rings from 0.3 to 2.2 μm at a scattering angle θ ∼ 175°. We calculate the G ring reflectance for size distributions of dust to kilometer-sized bodies derived from a physical, evolutionary model. The model tracks the evolution of the G ring from...
Clear-filter Viking images, and an accurate numerical model of the shape of Phobos, have been used to determine this satellite's photometric properties. A global-average Hapke function derived from disk-resolved data confirms previous indications that Phobos has a strong opposition surge. Photometrically corrected images were mosaicked into an albedo map; most of the resulting normal reflectances...
The results of impact experiments on solid CO 2 are presented. The resulting crater morphology has been measured (crater depth, diameter and volume). The data are for normal incidence impacts, at typically 5 km s −1 , of solid steel spheres of diameters 0.4 to 2.0 mm onto solid CO 2 . The size range of the projectiles permits a determination of the dependence of the crater...
We have studied the capture of planetesimals in Trojan orbits by a growing proto-Jupiter by integrating numerically the equations of motion of planetesimals in a four-body problem Sun–Jupiter–Saturn–planetesimal. The masses of Jupiter and Saturn increase exponentially with time. Nebular gas drag on small planetesimals is taken into account. We show that a fraction of the planetesimals near Jupiter's...
Ultraviolet spectra of Titan obtained with the Faint Object Spectrograph of the Hubble Space Telescope in October 1991 and August 1992 have yielded a disk-average geometric albedo of 0.02–0.044 from 1800–3300 Å. These results are in excellent agreement with previous UV measurements from 2200–3300 Å spanning two decades, but have a significantly higher signal to noise ratio and spectral resolution...
We study the rotation rate of a planet accreted from a disk of planetesimals with nonuniform spatial distribution. RecentN-body simulations of gravitational interactions between planetesimals and a protoplanet have shown that the spatial distribution of planetesimals in the vicinity of a protoplanet can become nonuniform because of strong gravitational perturbation by the protoplanet. On the basis...
Set the date range to filter the displayed results. You can set a starting date, ending date or both. You can enter the dates manually or choose them from the calendar.