Nebil Y. Misconi

Interplanetary dust dynamics III.Dust released from P/Encke:Distribution with respect to the zodiacal cloud

Abstract Numerical simulations of the trajectories of over 200 30-μm-radius dust particles released by Comet P/Encke were designed to study the evolution and redistribution of orbital elements as the dust particles spiral in toward the Sun. The dust assumes Jupiter crossing orbits immediately after release due to radiation pressure, while the comets orbit remains inside Jupiters orbital path. By the time the dust particles have spiraled past Jupiter, information on their origin from P/Encke is erased from the distribution in orbital elements. The primary objective of this study is to compare the observed spatial distribution of zodiacal/interplanetary dust with that of the model cloud inside Jupiters orbit. The observed location of the plane of maximum dust density “symmetry plane” of the zodiacal cloud is compared to a least-square-fit plane of the model cloud. A clear correlation between the two planes is found. The variation of the observed inclination and nodes with heliocentric distance agrees also, at least qualitatively, with that found in the model cloud. The hypothesis that short-period comets may have contributed in a major way to the zodiacal cloud is compatible with these results. The study is directly relevant to, and supports, Whipples suggestion that Comet P/Encke may have been a major source to the zodiacal cloud.

The photometric center of the Gegenschein

Model calculations are used to evaluate two factors which determine the position of the photometric center of the Gegenschein: the increased scattering efficiency of the interplanetary dust near backscattering (scattering angles θ ∼ 165–180°), and the spatial density distribution of the dust. Computer-generated brightness contours are used to investigate which of these two factors dominates. The code employs empirical scattering functions with and without a brightness enhancement in the backscattering region. It is found that the effect of the enhanced scattering of light by dust in the backscattering region overrides the effect of the spatial-density distribution of the dust. As a result, the photometric center should be observed at the antisolar point at all times, except possibly when the antisolar point is at its maximum displacement from the symmetry plane.

A Search for Small Scale Structures in the Zodiacal Light

Gegenschein observations from Pioneer 10 were found to have brightness structures with an amplitude of about 10% and a period of several to ten degrees in elongation. A search is made for such structures in high angular resolution ground-based observations from Mt. Haleakala, Hawaii. A new empirical method is used to correct for atmosphere-originated radiation. Background starlight is substracted using Pioneer 10 observations from beyond the asteroid belt. Preliminary analysis of the ground data also indicates the presence of small amplitude structures in the brightness distribution.

Small scale structure in the brightness of the zodiacal light - Ground-based observations

Ground-based observations of the evening zodiacal light taken by Weinberg and Mann from Mt Haleakala, Hawaii, during March 1966 are used to derive a table of zodiacal light brightnesses at spatial resolutions as small as 0.5° in differential ecliptic longitude λ-λ⊙, and 1.0° in ecliptic latitude β over the region 29.5° < λ-λ ⊙ < 56°, and −30° < β < +30°. Significant differences are found in the brightness distribution above and below the ecliptic plane. This is the first in a series of papers, on presentation and interpretation of observed small scale structures in the brightness of the zodiacal light. In this paper, we bring attention to a feature found in the brightness at all ecliptic latitudes, between differential ecliptic longitudes 39° and 42°.

Dynamical effects of jupiter, the inner planets, and Poynting-Robertson drag on the lifetime of interplanetary dust

Abstract Wyatt and Whipple (1950) identified a constant (W) in the relation between orbital semimajor axis (a) and eccentricity for interplanetary particles under the influence of Poynting-Robertson drag. Perturbations due to the planets were found to cause changes in W, including a nearly monotonie decrease for particles with semimajor axes less than 2 AU. Based on the calculated orbital evolution (Gustafson et al., 1987a) of some two hundred dust particles released from comet P/Encke and perturbed by the planets Venus, Earth, Mars, and Jupiter as well as radiation pressure and drag and corpuscular drag, values were found for the changes in W as a function of a. Most frequently, particles showed a decrease in W, corresponding to an increase in eccentricity over that predicted from P-R drag. This effect should be accounted for in future dynamical calculations that include Poynting-Robertson drag.

Brightness contribution of zodiacal dust along the line of sight in and out of the ecliptic plane and in the F-corona

Abstract Model calculations are used to determine the location of interplanetary dust particles that contribute most of the brightness of the zodiacal light as seen from Earth, in and out of the ecliptic plane and in the F-corona. It is found that as one observes in Increasing ecliptic latitude (β), the distance to the Earth decreases for dust contributing equal fractions to the line-of-sight brightness. This and other results will help in the analysis of: (1) structures in the observed brightness of the zodiacal light, (2) bands such as those observed by IRAS, (3) temporal variations in the brightness of the zodiacal light, (4) observations of the photometric axis, and (5) past and future observations of the F-corona.

The symmetry surface of the zodiacal cloud outside the earth's orbit

The location in space of the symmetry surface of the zodiacal cloud at elongation angles 110–140° from the Sun is determined from observations of the zodiacal light taken from the Pioneer 10 space probe, and from the zodiacal light experiment on Skylab. The inclination and ascending node of the symmetry surface from the ecliptic plane are shown to be about 1.2° and 23°, respectively, closest to those of the orbital plane of Mars. These results are consistent with those obtained from the Infrared Astronomical Satellite (IRAS) at elongation angle 90° from the Sun.

The size of the gravitational zone of influence of a planet acting on the orbital elements of small celestial bodies

Abstract Tisserands definition of the “sphere of action” of a planet is based on the equality of tidal vs. gravitational acceleration ratios of the sun and planet. Opik and others based their relation on equating the differential solar and planetary forces on the particle. Neither expression was formulated to describe the zone of influence surrounding a planet when considering the small but significant (i.e. long-term) perturbative effects of the planets on a particles orbital elements. For the purpose of determining these effects on interplanetary dust we dervive a zone of influence based on equating the gravitational forces of the sun and planet, and demonstrate its applicability by utilizing the particles closest approach to the planet as a measure of the zone of influence.