Asteroids meteorite-, link

Prior to discussing specific meteorite-asteroid (minor planet) links, we note that while >10 asteroids have been discovered, the spectral reflectances of only 1000-2000 are known. As white (Solar) light impinges on an asteroid s surface, its constituent minerals differ in reflectivity. Thus, the wavelength-reflectance dependence indicates the asteroid s major surficial constituent minerals and allows the asteroid to be classified by spectral type. The distribution of asteroid spectral type roughly varies with distance from the Sun [cf (/, 5, 6)]. The same spectrometer can be used to determine the spectral reflectance of a meteorite on Earth and asteroid/meteorite spectra can be compared (7/). 

The interpretation of cosmic-ray exposure ages of all kinds of meteorites links them to the asteroids from which they originated but which we have not yet been able to sample directly. The study of meteorites indicates that some asteroids contain resources that humans may be able to recover in the future (Kargel 1994 Lewis 1996). 

Asteroids have been a focus of spectroscopic studies for decades. Spectra obtained from telescopes on the Earth can identify some of the minerals that make up asteroids, but do not measure asteroid chemistry. Nevertheless, spectroscopic matches can be used to link some meteorite classes to then probable parent bodies, and thus allow indirect assessments of then chemical compositions. A few asteroids have been visited and analyzed by spacecraft. Chemical analyses require long data integrations from orbit or actually landing on the surface, and analyses of only two small near-Earth asteroids have been reported. 

Meteoritics involves the laboratory study of rocks without geologic context. Asteroid spectra provide a means to link some asteroid types to specific meteorite classes. Scientists can use the detailed information obtained from meteorites to reconstruct the chemical... 

Incident sunlight is partially absorbed by minerals on an asteroid s surface, and the fraction of light that is reflected can vary as a function of wavelength. Spectrophotometric studies of asteroids have been carried out for decades. Asteroid reflectance spectra have been compared to the spectra of meteorites measured in the laboratory (Fig. 11.3), providing a way to link some kinds of meteorites to possible parent bodies. Most measurements are made at visible wavelengths ranging from 0.4 to 1.0 pm, because the illuminating solar flux peaks... 

Besides long gas retention ages, three lines of evidence link all undifferentiated and most differentiated meteorites to asteroids mineralogy spectral reflectance and the orbits of nine meteorite falls. 

Meteorites are solid extraterrestrial materials that have survived the descent through the Earth s atmosphere. They are derived from meteoroids, which are natural objects with diameters of up to 10-100 m that orbit in space, while a meteor is the visible path of a meteoroid that enters the Earth s (or another body s) atmosphere (i.e., a shooting star). The meteoroids (and hence all meteorites) are ultimately derived from a parent body, from which they were separated by impact events that launched larger debris into new orbits. Most meteorite parent bodies appear to be in the asteroid belt, as can be inferred from orbits that were calculated for meteorites that were observed to fall [3]. Some meteorites have even been linked to specific asteroids, and there is good evidence that others are derived from Mars and the Moon (Table 10.1). As such, meteorites provide us with direct chemical and isotopic information on a large range of planetary bodies. Many meteorites furthermore... 

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