Other
Scientific paper
May 1967
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1967saosr.239.....w&link_type=abstract
SAO Special Report #239 (1967)
Other
14
Scientific paper
(1) On Maintaining the Meteoritic Complex, by F. L. Whipple. The meteoritic influx on the earth is derived from measurements of penetration of space vehicles, radio and photographic meteors, meteorite falls, Apollo asteriods, lunar craters, and comets. The total flux is some 2x 10-16 g cm-2 sec-1 on the surface of a corresponding nongravitating sphare. Such a cloud is self-destructive by collisions. It requires some 10 times the continuous contribution that the Poynting-Robertson effect alone would demand to maintain the zodiacal light and cloud, i.e. some 10 tons per second for quasi-equilibrium. This observational model is consistent with the etching rates observed on stone and iron meteorites and on photographic meteoroids. Various observational and theoretical facts indicate that the cloud up to masses of about 105 g is maintained by "live" comets. "Half-baked" asteriods, however, may compete with comets in contributing to the brighest fireballs. The stony meteorites may be maintained by collisional spallation from earth-crossing asteriods induced by smaller bodies, the Apollo asteroids being derived from the asteroid belt by the gravitational effects of Mars. The cometary meteoritic complex of smaller particles, carrying most of the mass, has a mean lifetime of some 1.7 X 105 yr. Certain puzzles remain in the orbital properties of the Apollo asteriods and of iron and stone meteorites. (2) Phase Function of the Zodiacal Cloud, by R. b. Southworth. Smith, Roach, and Owen's zodiacal-light photometry has been analyzed for the phase function and distribution of the particles. It is assumed that a) there is a unique phase function, b) the space density is the product of a distribution in heliocentric latitude and another in radius vector, and c) all the observed light is scattered by interplanetary particles symmetrically distributed about the sun, except for the enhancement at 65° elongation (possibly this is double scattering by ice in the high atmosphere). Various distributions in radius vector are tried, each yielding a phase function and a latitude distribution, and a predicted zodiacal-light distribution. Good fit to the observation are found with radial density distributions similar to that found from radar meteors; these also yield latitude distributions comparable to the meteor distribution. For scattering angles above 60°, the phase functions resemble a Lambert law, except for an extra peak near 180°, which could caused by particle roughness. (3) Space Density of Radio Meteors, by R. B. Southworth. The space density distribution of dust in the solar system is estimated from the orbits of approximately 13,000 radar meteors observed by the Harvard-Smithsonian Radio Meteor Project. Approximate corrections are made for unobservable classes of orbits and for other observational selection effects. Within the limits 0.1 to 10 a. u., the space density decreases monotonically outward from the sun. The distribution in heliocentric latitude has a very broad maximum centered on the ecliptic, and a deep minimum over the ecliptic poles. There is no evidence for any substantial enhancement of density in the asteroid belt. The distribution shows the effects of planetary perturbations and collisional destruction. (4) Orbital Distribution of Meteors of Limiting Magnitude +6 Observed from the Southern Hemisphere, by C. S. Nilsson. A radio survey of orbits of meteors of limiting magnitude +6 was carried out at adelaide, South Australia, during 1961. Each orbit has been weighted for observational and astronomical selection, and the distributions of 1900 orbits are compared to those of other surveys, particularly to those of the faint photographic survey of McCrosky and Posen. The distributions for stream orbits and sporadic orbits are given separately. The two most noteworthy distributions are those with perihelion distance and longitude of perihelion. The latter shows evidence of Jupiter alignment for the sporadic meteor orits, which, however, still does not differentiate between an asteroidal or cometary source.
Nilsson Carl S.
Southworth Richard B.
Whipple Fred L.
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