VNIR multispectral observations of rocks at Cape York, Endeavour crater, Mars by the Opportunity rover's Pancam

From its arrival at the portion of the rim of Endeavour crater known informally as Cape York, the Mars Exploration Rover Opportunity has made numerous visible and near infrared (VNIR) multispectral observations of rock surfaces. This paper describes multispectral observations from Opportunity's arrival at Cape York to its winter-over location at Greeley Haven. Averages of pixels from the Pancam's left and right eyes were joined to form 11 point spectra from numerous observations and were examined via a number of techniques. These included principal components analysis, a sequential maximum angle convex cone approach, examination of spectral parameters, and a hierarchical clustering approach. The end result of these analyses was the determination of six primary spectral (PS) classes describing spectrally unique materials observed on Cape York. These classes consisted of a "standard" outcrop spectrum that was observed on the clasts and matrix comprising the upper unit of the Shoemaker formation, a class representing rock surfaces exposed around Odyssey crater and typified by the rocks of the Tisdale series, pebbles occurring in and weathered out of the upper unit of the Shoemaker formation that appear red in 1009, 904, 754. nm color composites, patches on Tisdale rocks exhibiting a 864. nm band minimum that were spectrally anomalous in root mean square error images derived from spectral mixture analyses, clasts with a high 904. nm band depth occurring in the Greeley Haven location, and gypsum veins typified by the vein Homestake. Comparisons of three of these classes that had well defined band minima between 800 and 1009. nm with spectral library spectra of ferrous silicates and ferric oxide, oxyhydroxide and ferric sulfate minerals indicated tentative matches of the "red" pebbles with orthopyroxenes, of the spectrally anomalous 864. nm band minimum material with hematite or ferric sulfates, and of the high 904. nm band depth material with an orthopyroxene-clinopyroxene mixture. The spectral properties of rock surfaces on Cape York are distinct from those of Burns Formation outcrops observed on the Meridiani Plains. The Cape York outcrop is Noachian in age and study of these materials provides insight into less acidic environmental conditions extant before the formation of the Burns Formation.