ANALYZING REFLECTANCE SPECTRA OF MINERALS AND PLANETARY SURFACES

Using an ALTA® II reflectance spectrometer, the USGS digital spectral library, planetary spectra graphs, and a few mineral hand samples, one can teach and learn about the importance of light for studying planets and moons. The author created the hands-on, inquiry-based activity for an undergraduate planetary sciences course consisting of freshman to senior level science majors and non-majors. The activity follows a guided-inquiry approach that unites lab-based investigation of minerals with online datasets, and requires students to import, configure, graph, analyze, and compare data using spreadsheet software. The activity includes two parts: 1) analysis of mineral hand samples and spectra; 2) exploration of planetary reflectance spectra.

Part 1 of the activity begins by asking groups of students to use the ALTA® spectrometers to graph the spectrum (visible and some IR wavelengths) for one assigned (identified) mineral, and other unidentified available minerals; the procedure requires using a standard of measure to calculate an approximate reflectance for each of 11 wavelengths of light. The wavelength and reflectance data is entered into and graphed in a spreadsheet. Trends in the location (relative to wavelength) and magnitude of student-determined spectral peaks and troughs for the identified mineral are examined and compared to the USGS digital spectrum for the mineral; students import and graph several mineral spectra from the USGS digital library, and compare them to the student-determined graphs to narrow down and name the unidentified mineral samples. The first part of the activity enables students to learn how to use the ALTA® instrument, maneuver the mineral library, and manipulate data using the spreadsheet software. In Part 2, students go online to select planetary reflectance spectra to graph, import and manipulate data with the spreadsheet, and then familiarize themselves with the general and specific reflectance characteristics of several planetary surfaces, atmospheres, and ring systems. The activity culminates with students using techniques similar to those employed by planetary scientists to establish rationales for determining compositional information about, and categorizing and identifying, several planetary bodies in the solar system based solely on reflectance spectra.