Laboratory-based infrared spectral measurements of Mars analog materials collected from terrestrial field sites have long served as useful proxies for the interpretation of infrared spectra obtained from orbiting and surface instruments at Mars.  Typically, such measurements are made in two separate spectral regions spanning visible to near infrared (VNIR; 0.35 - 2.5 microns) and mid or thermal infrared (MIR/TIR; 5 - 50 microns) wavelengths as a result of the most commonly used spectrometers and their limited ranges.  This leads to both a gap in spectral coverage and a disparity in spectral characterization of a given material because many laboratories focus on only one of the two spectral regions.  Additional shortcomings result from variations in sample preparation and measurement spot size, precluding “apples to apples” comparisons across spectral regions.

These limitations and knowledge gaps can be overcome using a novel spectrometer accessory (Pike UpIR) designed for diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) measurements on materials ranging from prepared powders to unprepared rock hand samples of any size.  Paired with a spectrometer equipped with CsI optics and DLaTGS detector (Nicolet iS50R), spectra spanning ~1.4 – 50 microns in a single measurement can be obtained.  I have measured a range of samples from volcanic field sites (lava flows and ignimbrite deposits) using this setup and identified a diversity of secondary mineral phases including phyllosilicates, carbonates, and both amorphous and crystalline silica phases.  By virtue of the broad spectral range, I have recognized cases where the NIR is essentially blind to some alteration evident in the TIR and vice versa, a caveat especially relevant to rover-based observations of rocks.  Also noteworthy are carbonate coatings on some samples with spectra that do not resemble any of the many published carbonate spectra at either short or long IR wavelengths, and in some cases that display a vivid orange UV fluorescence.

By virtue of measuring spectra that include the 3.5 micron region, I am discovering a remarkable variation in the presence and strength of spectral features attributable to organic compounds, specifically lipids.  Where present and strong, the samples display a purple UV fluorescence.  Organic contaminants typically attributed to fingerprints or other oils do not display UV fluorescence, so the source of the lipids currently is unknown.