“El Capitan” Exposed!

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Caption:

These plots, or spectra, show that the rock collection dubbed "El Capitan" near the Mars Exploration Rover Opportunity's landing site at Meridiani Planum, Mars, consists of three primary mineral groups. These data were taken by the rover's miniature thermal emission spectrometer, which uses infrared detectors to determine the mineral composition of rocks and soil.

The top curve in the graph is the spectrum of an average sulfate mineral. The two curves in the center are the spectrum of "El Capitan" (white) and the best modeled fit (green) to that spectrum. The bottom curve shows a rock composed primarily of silicates and oxides without a sulfate component.

Spectral features centered near the light wavelength of 24 micrometers signify the presence of iron oxides. The broad, bowl-shaped feature between 8 and 12 micrometers represents silicate minerals. The sharp slope from 8 to 9 micrometers shows that "El Capitan" contains a considerable amount of sulfate.

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