Icarus
The first step of a development of a multipurpose numerical code for the realistic simulation of the circumnuclear coma of an active comet is described. First, the basic equations and numerical integration method are described; the adequacy of the method is demonstrated by a new computation of the interaction between two identical dusty water jets as treated in Y. Kitamura (1990, Icarus 86, 455-475)...
To understand jetting of earth materials, gabbro slabs (5 mm thick) were accelerated to 1.5-2 km sec - 1 and impacted gabbro (5-10 mm thick), novaculite (10 mm thick), and porous sandstone (12 mm thick) targets at inclination angles of 30 o -60 o . The ejecta were collected using a catcher box filled with styrofoam and the particles are extracted using chloroform. Jetting...
We are proposing a model for the delivery of volatiles to the inner planets by icy planetesimals (comets). Laboratory studies of the trapping of gases in ice forming at low temperatures simulate the formation of comet nuclei at various distances from the Sun in the solar nebula. The total gas content as well as the relative proportions of gases trapped in the ice are strong functions of temperature...
We present the results of numerical simulations for the long-term evolution of rotational states of near-prolate cometary nuclei over many orbits under sublimation-induced torques. We derive plausible evolutionary paths for the rotational states and show that they strongly depend on the location of active areas on the nucleus. We conclude that for acceptable locations of active regions on the nucleus,...
We present the results of laboratory measurements characterizing the near infrared spectrum of solid nitrogen at temperatures between 35 K and 60 K. The measurements show that the appearance of the spectrum in the regions of both the fundamental vibrational transition and its first overtone is temperature dependent. The temperature dependence of the spectrum in the overtone region provides a means...
We present a study of viscous overstabilities that can arise in a narrow ring whose particles are tightly packed, so that the pressure tensor exhibits a behavior different than that in a more dilute ring. The main objective of this work is to investigate the role of viscous overstabilities in the excitation of (azimuthal) eccentric modes in narrow rings. The problem is studied through an analytical...
A bright, slow moving, bolide observed during the 1989 AIDA campaign is shown to have been a very unusual near-Earth meteoroid. Data were obtained with five different instruments and these observations have now been extensively analyzed. Various indicators point to a stony object and spectroscopic observations in the near IR show two Fe I emissions with an excitation temperature of 3100 K. A third...
We present evidence of an unusual and previously unidentified feature in Saturn's outer B ring at a radius of 117,130 km. The Voyager 2 optical occultation experiment shows a step in opacity, dropping from 1.4 to 0.5 across several kilometers and generally remaining low out to the edge of the ring. By contrast, the Voyager 1 radio occultation showed no distinct change at this location, a rare lack...
A sample of over 12,487 asteroid proper element triplets, computed by A. Milani and Z. Knezevic (1994, Icarus 107, 219-254), has been searched for statistically significant and robust families by both the hierarchical clustering (HCM) and the wavelet analysis (WAM) automated techniques. The current sample includes almost 8000 unnumbered objects with relatively well-determined orbits, which allow us...
The time variation of the flux of new Jupiter-dominated Oort cloud comets is considered here. It has previously been demonstrated that the major perturbation of these comets during the present epoch is due to the tidal field of the relatively smooth distribution of matter in the galactic disk. Over long time scales, secondary sources of the near-parabolic comet flux are stellar and molecular cloud...
We attempt to estimate the size range of particles that are ejected from a protostellar accretion disk by a protostellar jet. An n-body code is used to determine the subsequent motion of the ejected particles, where the particles are subject to two forces: the gravitational attraction from the protostar and the gas drag from the halo gas of the accretion disk.It is highly probable that a protosolar...
We have carefully monitored the radial velocities of 21 bright, solar-type stars for 12 years, None has shown any reflex motion due to a substellar companion to an upper limit of between 1 and 3 Jupiter masses (X sin i) for orbital periods less than 15 years, We can also rule out companions of more than 3 to 10 Jupiter masses (X sin i) at much longer periods based on long-term trends in the radial...
The dynamical state of the Pluto-Charon binary is distinctive in several respects including its well-known position in the Neptune 3:2 mean motion resonance, its librating argument of perihelion, and its high heliocentric eccentricity and inclination. Here we present a suite of numerical simulations of bodies in the outer Solar System which demonstrate that Pluto's high-heliocentriceccentricity and...
Spectra of the 4-μm continuum of the polar regions of Jupiter were obtained at the Canada-France-Hawaii Telescope. These spectra were compared with a low-resolution spectrum of the equatorial region obtained at the United Kingdom Infrared Telescope. The comparison shows that the continuum level of the equatorial spectrum is at least five times higher than those of the polar spectra. It was also found...
Gravitational instability of a particle layer in the solar nebula is inhibited by effects of the nebular gas. Particles must grow to at least meter size in order to decouple from shear-generated turbulence and allow the layer to reach critical density. The radial velocity dispersion induced by drag further delays onset of instability until the mean size is ~10-100 m. This velocity dispersion, with...
The reaction between C 2 H 3 and H 2 has been suggested to be potentially important in accounting for observational data on the abundance of low-molecular weight hydrocarbons in the atmospheres of the giant planets, especially the ratio of [C 2 H 6 ]/[C 2 H 2 ] in the jovian stratosphere. Previous values of the rate constant for this reaction...
We have numerically integrated the full three dimensional rotation of Hyperion using as initial conditions the moments of inertia, pole position, and spin rate from a solution based on fitting control points, limb, and terminator positions in high-resolution Voyager 2 images (P. C. Thomas et al. 1995, Icarus ). These images were taken over a 38-hr period and cover ~114 o of rotation. From...
About 10,000 km of trenches in chasmata and coronae have been identified as possible sites of retrograde subduction on Venus. All the sites have narrow deep trenches elongate along strike with arcuate planforms, ridge-trench-outer rise topographic profiles typical of terrestrial subduction zones, large outer rise curvatures >10 - 7 m - 1 , fractures parallel to the strike...