LOOKING BACK AT THE FIRST HYPERSPECTRAL INSTRUMENTS ON THE SURFACE OF ANOTHER PLANET AND FORWARD TO THE NEXT ONES (Invited Presentation)

In 2004, two Miniature Thermal Emission Spectrometers (Mini-TES) arrived on the surface of Mars aboard the Spirit and Opportunity rovers. Using Fourier transform infrared spectroscopy spanning the thermal infrared wavelengths from ~2000 to 340 cm^-1 (~5 to 29 μm) at ~10 cm^-1 resolution (167 channels), the twin Mini-TES instruments represent the first hyperspectral mineral remote sensors on a planetary surface beyond Earth. Both greatly exceeded their design life and specifications, supplying ground truth for orbital mineral remote sensing and contributing to key discoveries, including hints of evidence for ancient life on Mars.

Mini-TES observations from the plains of Gusev crater demonstrated the ubiquity of olivine-rich basaltic rocks, with additional examples lofted into the adjacent Columbia Hills by meteor impacts. Hundreds of rocks observed with Mini-TES in the Columbia Hills display spectral characteristics of increasing alteration, but likely with very little water involved. Other volcanic rocks show little evidence of chemical alteration in most cases, but rare exceptions include a tephra deposit cemented by Mg-Fe carbonates. Unambiguous evidence of hydrothermal processes was identified by Mini-TES in the form of rocks composed of opaline silica, likely indicative of a hot spring/geyser environment. Onboard the Opportunity rover, Mini-TES confirmed the orbital detection of crystalline hematite at Meridiani Planum and spectral characteristics indicative of a transition from a precursor goethite phase. The light-toned sedimentary bedrock that hosts the hematite has spectral features consistent with Al-rich opaline silica, Mg-, Ca-, and Fe-bearing sulfates, plagioclase feldspar, and nontronite. Rare rocks at both landing sites are recognizable as iron meteorites from their infrared reflective properties.

The next Mars rovers from NASA and ESA, launching in 2020, will carry hyperspectral visible/near/shortwave infrared hyperspectral instruments, as well as Raman spectrometers. A new era of mineral remote sensing from the surface of Mars will begin with their successful arrival in 2021.