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Painting a Mineralogic Picture
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Painting a Mineralogic Picture

October 23, 2009
While the NEAR Shoemaker spacecraft orbits Eros at low altitudes, its near-infrared spectrometer is slowly but systematically building a detailed map of the asteroid's surface mineralogy. Every few seconds, the instrument measures the spectrum of sunlight reflected from a small portion of Eros' surface, called the instrument's "footprint." Over the course of weeks, many tens of thousands of such spectra are accumulated, each accompanied by pointing information that allows analysts to project the spectrum onto the asteroid's surface. The spectra are sorted to identify those with the strongest signal from the asteroid, and those are projected onto a model of Eros' shape to make a spectral map. This map can then be analyzed to determine the mineralogy of different parts of the surface.

This graphic shows the projection of one footprint taken April 28, 2000, from an orbital altitude of 55 kilometers (34 miles). The accompanying information, for "bookkeeping" individual spectra, includes the time of the measurement and the observation sequence during which the spectrum was measured.