Techniques d'observation spectroscopique d'astéroïdes

70 CHAPTER 4. SPECTRAL ANALYSIS TECHNIQUES
(a)
(b)
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Figure 4.2: a) The photomicrograph of a thin section of the carbonaceous chondrite Allende, which was seen to
fall in Chihuahua, Mexico on the night of February 8, 1969. Numerous round silicate chondrules together with
irregular inclusions can been observed . b) Comparison of solar-system abundances (relative to silicon) determined
by solar spectroscopy and by analysis of carbonaceous chondrites [Ringwood, 1979].
primary means by which planetary body evolve. The bulk compositions of achondrites are
enriched in litophile and chalcophile elements.The abundances of these elements are also enhanced
in the Earth’s crust. Achondrites are significantly depleted in iron and siderophile elements.
The subtypes of achondritic meteorites include: Howardite - Eucrite - Diogenite (HED),
Aubrites, Shergottite - Nakhlite - Chassignite (SNC), Ureilites, Acapulcoites and Lodranites.
A small percentage of known achondrites are from two larger bodies - the Moon and Mars
[de Pater & Lissauer, 2010].
Several spectral libraries are available for accomplishing spectral comparison, such as Relab
2 , USGS Spectroscopy Laboratory 3 , the Johns Hopkins University (JHU) Spectral Library,
the Jet Propulsion Laboratory (JPL) Spectral Library 4 , etc. I used the Relab spectral library,
which is one of the largest libraries and contains more than 15,000 spectra for different types
of materials from meteorites to terrestrial rocks, man-made mixtures, and both terrestrial and
lunar soils.
4.1.3 Space weathering effects
It is now widely accepted that the space environment alters the optical properties of airless
body surfaces (Fig. 4.3). Space weathering is the term that describes the observed phenomena
caused by these processes operating at or near the surface of an atmosphere-less solar system
body, that modify the remotely sensed properties of this body surface away from those of the
unmodified, intrinsic, subsurface bulk of the body [Chapman, 1996, 2004].
2 http://www.planetary.brown.edu/relab/
3 http://speclab.cr.usgs.gov/
4 http://speclib.jpl.nasa.gov/