Color Commentary: A Summary of Multispectral Imaging W.H. Farrand1, J.F. Bell2, J.R. Johnson3, M.S. Rice4, A. Wang5 1. Space Science Institute, Boulder, CO; [email protected] Results from the and Rover Missions 2. Arizona State University, Tempe, AZ 3. Johns Hopkins University, Applied Physics Lab, Laurel, MD Introduction: 4. Western Washington University, Bellingham, WA In the 2208 and 5111 sols of the Exploration Rovers (MER) Spirit and Opportunity’s missions, a completely new perspective of the 5. Washington University at St. Louis, St. Louis, MO compositional diversity of the Martian surface and shallow subsurface layer was gained. Rocks and soils making up ancient terrains were lithologically, chemically and mineralogically diverse. This diversity was evidenced by measurements of multispectral reflectance in the visible Opportunity: Crater and near infrared (VNIR) made by the MER Pancam sensors. The Spirit and Opportunity archive of multispectral data represents not only a color record of the terrains explored by the rovers, but also provide valuable information on materials never examined in situ, but that Fig. 12. Cape York rocks nonetheless might be investigated in terms of their multispectral character for better understanding the geologic history of the explored A. Sol 2694 P2594 L357 Tisdale-1. B. Sol terrains. This abstract provides a sampling of multispectral Pancam observations of rocks and soils made over the course of the Spirit and 3029 P2376 L257 Grasburg fm. C. Sol 2969 Opportunity missions. P2591 L257 Monte Cristo veins. D. Sol 3074 P2564 L357 Whitewater Lake. E. Sol 3067 The Pancam Sensors: P2560 L257 Kirkwood “newberries”. F. Sol Each Pancam collected 11 spectrally unique channels in the 430 to 1010 nm wavelength range. There were 2 overlapping channels for red 3103 P2587 L257 Lihir/Esperance boxwork. or blue stereo for a total of 13 filters ("13f") devoted to geologic analyses. These data were converted to radiance factor and then to relative reflectance (R*) by dividing radiance factor by the cosine of the solar incidence angle. More details on the Pancam instrument and its calibration are provided in [1,2].

Spirit: The Gusev Plains & Columbia Hills Opportunity: The Meridiani Plains

Fig. 7. A. Sol 33 P2589 L256 (753, 535, 482 nm) view of target Cathedral Dome. B. Spectra of primary units. Fig. 13 Spectra of major Cape York rock units.

Fig. 1: A. Sol 100 P2544 Rt. 66 RAT brush “daisy”. L357 (673, 535, 432 nm). B. Spectra of bright drift (red) and brushed basalt (black). Fig. 8. A. Sol 37 A P2589 RAT grind L256 composite. B. Spectra of RAT cuttings and library B hematite convolved B to Pancam A bandpasses.

Fig. 2. L256 (753, 535, 482 nm) mosaic of “Big Hole” trench from sol 116 and described in terms of spectral and chemical character in [3]. Fig. 14. Mosaic of Spirit of St. Louis with overlay of decorrelation stretched images with ellipse highlighting “red zone”.

Fig. 15. Scuff area on (c) Knudsen Ridge, south flank of Marathon Valley. C A. Sol 4379 Scuff area P2583 L357. B. DCS of 13A. C. Spectra of circled pebbles showing possible Fig. 9. Rinds on Burns formation outcrop. A. Sol 556 P2584 A sulfate feature (indicated “Fruitbasket” L357. Decorrelation stretch (DCS) of Fig. 8A. Rinds B by arrow) nominally appear blue on rock surface. similar to that seen in Arad (Fig. 5).

Fig. 4. Spectra of 14 candidate spectral classes from plains to Home Plate (after [4]). Fig. 3 Stretched color images of representative Columbia Hills & Home Plate rock spectral classes [4]. A. sol 736 Cang Jie, Plains basalt. B. Sol 227B Frio West Spur class. C. Sol 409 Watchtower class. D. Sol 487 Davis, Jibsheet class. E. Sol 647 Aster, Methuselah class. F. Sol 536 Independence class. G. Sol 689 Wolf Lake, Seminole Class. H. Sol 764 Stars spectral class (Home Plate). I. Sol 753 Posey spectral class (Home Plate).

Fig. 5. A. Sol 721 Fig. 16. Spectra of Mn-rich materials observed P2538 L357 on rim of Endeavour crater. disturbed soil Arad. Fig. 10. Plot of 535 nm band depth vs 535 to 601 nm 3+ B. DCS of Fig. 5A. slope of Fe bearing minerals compared to Meridiani Fig. 17. Mn-rich materials [7,8]. A Sol 3555 P2531 L357 Pinnacle Island, arrow C. Spectra of white outcrop (after [6]) showing that in terms of reflectance, marks Mn-rich patch. B.Sol 4882 P2552 L357 La Bajada, putative Mn-rich circled. (sulfate-rich) soil and the outcrop plots between goethite and ferrihydrite. C. Sol 3419 P2559 L357 Monjon, arrow marks Mn-rich coating. D. Same scene as red (disturbed C, but 535 nm band depth image. surface airfall soil). Broad 800 nm band Conclusions: of former attributed to Fe sulfates The multispectral imaging capabilities of the Spirit and Opportunity Pancam sensors enabled the detection of a variety of compositionally distinct materials that were investigated in greater detail with in situ analysis. This ability to “scout out” interesting materials proved invaluable over each rover’s mission. This capability has also proved important with the MSL Mastcam [9] and will undoubtedly be vital as exercised by the Mars 2020 Mastcam-Z [10] and ExoMars PanCam [11].

References: [1] Bell, J.F. III (2003) JGR, 108, doi:10.1029/2003JE002070. [2] Bell III, J.F. et al. (2006) JGR, 111, 10.1029/2005JE002444. [3] Wang A. et al. (2006) JGR, 111, 10.1029/2005JE002513.[4] Farrand W.H. et al. (2008) JGR, 113, 10.1029/2008JE003237. [5] Rice M.S. et al. (2010) Icarus, 205, 375-395. [6] Farrand W.H. et al. (2007) JGR, Fig. 11. A. Sol 352 P2596 L357 view of 112, 10.1029/ 2006JE002773. [7] Farrand W.H. et al. (2016) Am. Min., 101, 2005-2019. [8] Arvidson R.E. et al. (2016) iron meteorite. B. DCS of 11A. Arrows indicate rind Am. Min., 101, 1389-1405. [9] Bell et al. (2017) Earth and Space Science, 4, 396–452. [10] Bell et al. (2016) 3rd Int. patches. Workshop on Instr. Plan. Missions, No. 1980, id.4126. [11] Cousins et al. (2012) Plan. Space Sci., 71, 80-100. Fig. 6. Si-rich materials with hydration feature noted by [5]. A. Sol 1160 P2582 Elizabeth Mahon. B. Sol 1198 P2539 Kenosha Comets. C. spectra noted by red rectangles in A and B. 934 to 1009 nm downturn attributed to hydration [5]. Acknowledgements: The first author has been funded as a MER Participating Scientist.