Meteorite transport—Revisited

Meteorites are delivered from the asteroid belt by way of chaotic zones (Wisdom 1985a). The dominant sources are believed to be the chaotic zones associated with the ν₆ secular resonance, the 3:1 mean motion resonance, and the 5:2 mean motion resonance. Though the meteorite transport process has been previously studied, those studies have limitations. Here I reassess the meteorite transport process with fewer limitations. Prior studies have not been able to reproduce the afternoon excess (the fact that approximately twice as many meteorites fall in the afternoon as in the morning) and suggested that the afternoon excess is an observational artifact; here it is shown that the afternoon excess is in fact consistent with the transport of meteorites by way of chaotic zones in the asteroid belt. By studying models with and without the inner planets it is found that the inner planets significantly speed up the transport of meteorites.     

La Malbaie Structure,Quebec—A Palaeozoic Meteorite Impact Site

Abstract Evidence in support of an origin by meteorite impact has been found at La Malbaie structure, 105 km northeast of Quebec City on the north shore of the St. Lawrence River. The structure has a central peak (Mont des Eboulements) 2500 feet (780 meters) above sea level, surrounded by lower hills and a semicircular valley with a diameter of 35 km. The circularity is incomplete as the peripheral valley terminates to the south and east at the St. Lawrence River which obscures an estimated 40 per cent of the crater. Rocks within the crater comprise charnockitic and granitic gneisses, anorthosite and gabbro of Precambrian Grenville age, and Middle Ordovician limestone.     

Withrow — a New Iron Meteorite from the State of Washington

Abstract. About 1950 an iron meteorite weighing 19 1/4 pounds was found a mile west of Withrow in Douglas County, Washington. The discovery site happens to be a little less than 5 miles SSE from that of the Waterville meteorite. However, the two irons are definitely not from a single fall. Withrow is a medium octahedrite showing secondary recrystallization of the type ascribed to cosmic heating. It was apparently picked up not more than a few years after it fell. Weathering is minimal, and effects of passage through the atmosphere are well preserved.     

Artificial electron clouds—II General considerations

This is the second in a series of papers which deals with the creation of artificial electron clouds by the ejection of proper contaminants into the upper atmosphere. It presents those general considerations which are common to the several papers to follow. A square-well model is used to describe the distribution of the ejected contaminant immediately after the fast initial expansion. The diffusion equation is applied to this model and the salient features are noted. Basic equations are applied to this simplified model to describe the electron generative and decay processes on a term-by-term basis, in order to ascertain the relaxation times involved for the several interrelated problems. Chemical consumption of the alkali metal contaminant by reaction with the ambient species is found to be negligible above 95 km. It is concluded that “for generation methods similar to those outlined here the practical altitude limits of generation of long lived electron clouds is between about 70 and 200 km; chemical consumption determines the lower while the diffusion process establishes the upper limit.     

The Oshkosh Meteorite

Abstract In the fall of 1961, fragments of an olivine-bronzite chondrite were found about 2 miles NNW of Oshkosh, Wisconsin, the total weight being 144.8 g. This paper fixes the exact location and describes the circumstances of the find.     

Meteorite fusion crust variability

Abstract— Two assumptions commonly employed in meteorite interpretation are that fusion crust compositions represent the bulk‐rock chemistry of the interior meteorite and that the vesicles within the fusion crust result from the release of implanted solar wind volatiles. Electron microprobe analyses of thin sections from lunar meteorite Miller Range (MIL) 05035 and eucrite Bates Nunataks (BTN) 00300 were performed to determine if the chemical compositions of the fusion crust varied and/or represented the published bulk rock composition. It was determined that fusion crust compositions are significantly influenced by the incorporation of fragments from the substrate, and by the composition and grain size of those minerals. Because of compositional heterogeneities throughout the meteorite, one cannot assume that fusion crust composition represents the bulk rock composition. If the compositional variability within the fusion crust and mineralogical differences among thin sections goes unnoticed, then the perceived composition and petrogenetic models of formation will be incorrect. The formation of vesicles within these fusion crusts were also compared to current theories attributing vesicles to a solar wind origin. Previous work from the STONE‐5 experiment, where terrestrial rocks were exposed on the exterior of a spacecraft heatshield, produced a vesicular fusion crust without prolonged exposure to solar wind suggesting that the high temperatures experienced by a meteorite during passage through the Earth's atmosphere are sufficient to cause boiling of the melt. Therefore, the assumption that all vesicles found within a fusion crust are due to the release of implanted volatiles of solar wind may not be justified.     

Finding a New Meteorite

Following is an account of the incidents relevant to the discovery of several new meteorites, in particular a small stony specimen (an aerolite) weighing about 4 pounds, found recently on a farm in the northern part of Cowley County, Kansas.     

The Belle Plaine III Meteorite

Abstract The Belle Plaine III meteorite is one of three meteorites, all of about the same size, found within a 2 mile strip southeast of Belle Plaine, Kansas. The meteorite weighs 23.9 kg, and consists of about 28% metallic minerals and 72% silicates. Nickel-iron, magnetite, hypersthene and olivene are the major constituents. The meteorite is an olivene-hypersthene chondrite.     

Lanai Meteorite Crater Apparently Myth

Abstract A survey by air and on the ground revealed no depression at the place supposedly called Ka-imu-hoku, Hawaiian for “The Star Oven”, on the island of Lanai. It had been reported as a “pit in the sand” or “the place where a meteor fell”. Reasons are given for believing the name was based on native observation of a nineteenth century fireball.     

Meteorite 3‐D synchrotron microtomography: Methods and applications

Abstract— Methods of synchrotron X‐ray computed microtomography (XRCMT) are described, which allow nondestructive, high spatial and contrast resolution imaging of the density structures of meteorites and their components in three dimensions. Images of bulk chondrites (to one cubic centimeter in size) reveal compound chondrules, chondrule/matrix volumetric ratios, metal and sulfide distribution, petrofabrics, and 3‐D chondrule and calcium‐aluminum inclusion (CAI) sizes and shapes. Images of separated chondrules and CAIs reveal void spaces, mineral intergrowth textures, and the true locations of crystal rims and cores, at resolutions to <8 cubic micron/volume element. Images of achondrites reveal mineral fabrics and crystal zoning. Lunar glass spherules can be searched for phenocrysts bearing deeply sourced melt inclusions. A companion DVD and URL contain images for classroom and research use. Numerical techniques for quantification of X‐ray computed microtomography (XRCMT) data and its potential applications are discussed. Three‐dimensional X‐ray images of meteorites provide a way to discover components of interest and to precisely slice samples to expose these components with minimal damage and loss of material. Three‐dimensional studies of petrographic features (size, shape, texture, and modal abundance) of chondrites and their components, as well as other meteorites, have definite advantages over standard 2‐D studies using randomly sliced thin sections.     

Meteorite finds from southern Tunisia

Abstract— We report on the meteorite search campaign of April 2008, conducted by a joint Tunisian‐Italian scientific expedition in southern Tunisia (Dahar region). Nine likely unpaired meteorites (seven H‐class and two L‐class chondrites) totalling ?1.3 kg were recovered by exploring an approximately 45 km²area, therefore demonstrating that southern Tunisia is a suitable terrain for systematic searches for meteorites.     

An Iron Meteorite from Akyumak

Abstract— The microstructure of an iron meteorite which fell near Akyumak, East Anatolia, Turkey on 2 August 1981 has been examined and its composition determined. The Ni content is 7.7% and kamacite bandwidth is 0.32 ± 0.06 mm. The kamacite contains Neumann bands and some daubreelite inclusions. Taenite and plessite account for about 45 to 50% of the metal; finger, cellular and net plessite are observed. Gallium (1.9 ppm), Ge (< 40 ppm) and Ir (1.81 ppm) were determined by neutron activation. The microstructural observations and chemical data show Akyumak to be a fine octahedrite and a member of group IVA.     

Satellite resonance with longitude-dependent gravity—II Effects involving the eccentricity

For a satellite in a nominally circular orbit at arbitrary inclination whose mean motion is commensurable with the Earth's rotation, the dependence of gravity on longitude leads to a resonant variation in eccentricity as well as the long-period oscillation in longitude. Provided forces capable of processing perigee are present, it is shown that the change in eccentricity for a satellite captured in librational resonance is not secular but periodic.

There are corresponding resonance effects for a satellite in a nominally equatorial but eccentric orbit. Here the commensurability condition is that the longitudes of the apses shall be nearly repetitive relative to the rotating Earth. There will be a long-period oscillation in longitude which can take the form of either a libration (trapped) or a circulation (free), and there will also be an oscillation of the orbital plane having the same period as the precession of perigee relative to inertial space.     

High Inclination Meteorite Streams can Exist

Meteorites represent bodies at the larger end of the meteoroid size spectrum since they are large enough to survive ablation in the Earth’s atmosphere. They are thus far less numerous than normal meteoroids that become meteors. A number of meteorites can arrive at around the same time and location and so in some sense represent a stream, but these are just recent fragmentations. Most meteors, according to their cosmic ray exposure age are at least 10 million years old. This is roughly also the timescale for the onset of chaos in the inner Solar System and so conventional wisdom is that meteorites can not survive on such orbits for such a time span and that they certainly cannot survive as coherent streams. We investigate numerically the survival of streams for this time interval.     

Destination: Earth. Martian Meteorite Delivery

The delivery dynamics of martian meteorites are examined by means of a direct numerical simulation of their orbital evolution. The dynamics in the martian region are dominated by secular resonant effects, not by close encounters with Mars. These secular effects rapidly (∼1 Myr) transport martian ejecta to Earth-crossing orbits. The measured cosmic-ray exposure ages of the martian meteorites are consistent with their being directly launched as small bodies from the martian surface by impacts over the last ?15 Myr. Collisional effects and being driven into the Sun efficiently destroy martian meteoroids in space on time scales of order 10 Myr. The implications of these results for the launch mechanism and microorganism transport are discussed.     

Some special restricted four-body problems—II. From Caledonia to Copenhagen

Special analytical solutions are determined for restricted, coplanar, four-body equal mass problems, including the Caledonian problem, where the masses M_i = M for i = 1,2,3,4. Most of these solutions are shown to reduce to the Lagrange solutions of the Copenhagen problem of three bodies by reducing two of the masses (m_i = m for i = 1,2) in the four-body equal mass problem to zero while maintaining their equality of mass. In so doing, families of special solutions to the four-body problem are shown to exist for any value of the mass ratio μ = m/M.     

Meteorite and meteoroid: New comprehensive definitions

Abstract– Meteorites have traditionally been defined as solid objects that have fallen to Earth from space. This definition, however, is no longer adequate. In recent decades, man‐made objects have fallen to Earth from space, meteorites have been identified on the Moon and Mars, and small interplanetary objects have impacted orbiting spacecraft. Taking these facts and other potential complications into consideration, we offer new comprehensive definitions of the terms “meteorite,”“meteoroid,” and their smaller counterparts: A meteoroid is a 10‐μm to 1‐m‐size natural solid object moving in interplanetary space. A micrometeoroid is a meteoroid 10 μm to 2 mm in size. A meteorite is a natural, solid object larger than 10 μm in size, derived from a celestial body, that was transported by natural means from the body on which it formed to a region outside the dominant gravitational influence of that body and that later collided with a natural or artificial body larger than itself (even if it is the same body from which it was launched). Weathering and other secondary processes do not affect an object’s status as a meteorite as long as something recognizable remains of its original minerals or structure. An object loses its status as a meteorite if it is incorporated into a larger rock that becomes a meteorite itself. A micrometeorite is a meteorite between 10 μm and 2 mm in size. Meteorite– “a solid substance or body falling from the high regions of the atmosphere” ( Craig 1849 ); “[a] mass of stone and iron that ha[s] been directly observed to have fallen down to the Earth’s surface” (translated from Cohen 1894 ); “[a] solid bod[y] which came to the earth from space” ( Farrington 1915 ); “A mass of solid matter, too small to be considered an asteroid; either traveling through space as an unattached unit, or having landed on the earth and still retaining its identity” ( Nininger 1933 ); “[a meteoroid] which has reached the surface of the Earth without being vaporized” (1958 International Astronomical Union (IAU) definition, quoted by Millman 1961 ); “a solid body which has arrived on the Earth from outer space” ( Mason 1962 ); “[a] solid bod[y] which reach[es] the Earth (or the Moon, Mars, etc.) from interplanetary space and [is] large enough to survive passage through the Earth’s (or Mars’, etc.) atmosphere” ( Gomes and Keil 1980 ); “[a meteoroid] that survive[s] passage through the atmosphere and fall[s] to earth” ( Burke 1986 ); “a recovered fragment of a meteoroid that has survived transit through the earth’s atmosphere” ( McSween 1987 ); “[a] solid bod[y] of extraterrestrial material that penetrate[s] the atmosphere and reach[es] the Earth’s surface” ( Krot et al. 2003 ).     

Meteorite stranding surfaces and the Greenland icesheet

Abstract— Thirty years of recoveries in East Antarctica have led to significant understanding of the regional characteristics associated with meteorite stranding surfaces. In Antarctica these sites are characterized by patches of snow‐free blue ice at high altitude on the icesheet in regions where iceflow is highly restricted. Melting is extremely rare or absent and sublimation rates are high, even though meteorite stranding surfaces are predominantly found within regions where accumulation typically dominates. Localized environmental conditions that persist for thousands of years or longer appear to be the dominant factor rather than shorter‐term or seasonal cycles. In this paper we describe our discovery of regions in Northeast Greenland with blue ice areas that exhibit many of the requisite characteristics, suggesting that they are excellent prospects for future meteorite recovery efforts.