W. M. Calvin

Publications (27)176.05 Total impact

• Source

  Available from: Nathalie A. Cabrol

  Dataset: Overview

  R. E. Arvidson, S. W. Squyres, R. C. Anderson, J. F. Bell, D. Blaney, J. Brückner, N. A. Cabrol, W. M. Calvin, M. H. Carr, P. R. Christensen, [......], L. A. Soderblom, R. Sullivan, S. D. Thompson, N. J. Tosca, A. Wang, H. Wanke, J. Ward, T. Wdowiak, M. Wolff, A. Yen
• Source

  Available from: Christian Schröder

  Article: Exploration of Victoria crater by the Mars rover Opportunity.

  S W Squyres, A H Knoll, R E Arvidson, J W Ashley, J F Bell, W M Calvin, P R Christensen, B C Clark, B A Cohen, P A de Souza, [......], T J McCoy, S M McLennan, D W Ming, D W Mittlefehldt, R V Morris, J W Rice, C Schröder, R J Sullivan, A Yen, R A Yingst
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  ABSTRACT: The Mars rover Opportunity has explored Victoria crater, an approximately 750-meter eroded impact crater formed in sulfate-rich sedimentary rocks. Impact-related stratigraphy is preserved in the crater walls, and meteoritic debris is present near the crater rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the crater walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those approximately 6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.
  Science 06/2009; 324(5930):1058-61. · 31.20 Impact Factor
• Article: Evidence for a Possible Siliceous Sinter Deposit at Home Plate in Gusev Crater

  S. W. Ruff, J. D. Farmer, W. M. Calvin, J. R. Johnson, R. E. Arvidson, S. W. Squyres, P. R. Christensen
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  ABSTRACT: Instruments from the Athena payload on the Mars Exploration Rover Spirit in Gusev Crater have identified materials remarkably enriched in silica. Spectra from the Miniature Thermal Emission Spectrometer (Mini-TES; ~5-25 microns) and Alpha Particle X-ray Spectrometer have revealed a high-silica phase in light-toned soil and heavily eroded outcrops extending as much as 50m from the low-lying, layered plateau known as Home Plate. The various forms of silica (SiO2) are readily distinguishable in the thermal infrared (TIR) wavelengths as is their purity. The Mini-TES spectra clearly indicate an amorphous phase with silica content >80% that is most similar to opal-A, the least crystalline form. The presence of amorphous silica is consistent with a variety of primary and secondary origins including obsidian, high-silica rhyolite/tuff, acidic alteration/leaching of silicate rocks, and precipitation from silica-saturated fluids. The Mini-TES spectra contain a prominent absorption near 8 microns and an emissivity maximum near 12 microns that depart from typical opal-A. Existing literature and new laboratory measurements demonstrate that these features can arise in certain forms of amorphous silica as a function of both geometric and scattering effects. The feature near 8 microns that typically appears as a shoulder in opal-A becomes a prominent absorption minimum with increasing emission angle as well as with the presence of porosity at the scale of a few 10s of microns. An emission peak near 12 microns is accentuated as a result of scattering due either to porosity or particle-size effects. Both of these features are common to siliceous sinter deposits that form as sedimentary precipitates around hydrothermal springs on earth. The Mini-TES spectra display these features and are best fit by spectra of natural sinter samples that contain microporosity and are measured at the high emission angles (>45 degrees) typical of Mini-TES observations. Primary igneous forms of amorphous silica such as obsidian and high-silica glass found in tuffs do not provide a good fit to the Mini-TES spectra. We have not explored fully the spectral characteristics of amorphous silica produced from acid alteration environments such as fumaroles, so this origin for the high-silica materials remains viable. However, their proximity to the Home Plate structure, which appears to be a depression buried by pyroclastic deposits, leads to the hypothesis that Home Plate represents a buried hot spring with an associated apron of siliceous sinter. Continued exploration of the site by the Spirit rover is intended to further investigate this hypothesis as well as the alternative hypothesis of a fumarolic origin for the high-silica materials.
  AGU Fall Meeting Abstracts. 11/2007; -1:1097.
• Article: Hematite Spherules at Meridiani: Results from MI, Mini-TES and Pancam

  W. M. Calvin, J. D. Shoffner, J. M. Pocock, J. R. Johnson, A. T. Knudson, D. Rogers, T. D. Glotch, S. W. Ruff
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  ABSTRACT: A synthesis of observations of the hematite spherules support their formation as concretions and shows variation as Opportunity has traversed various facies.
  LPI Contributions. 06/2007; 1353:3163.
• Source

  Available from: William Farrand

  Article: Two years at Meridiani Planum: results from the Opportunity Rover.

  S W Squyres, A H Knoll, R E Arvidson, B C Clark, J P Grotzinger, B L Jolliff, S M McLennan, N Tosca, J F Bell, W M Calvin, W H Farrand, T D Glotch, M P Golombek, K E Herkenhoff, J R Johnson, G Klingelhöfer, H Y McSween, A S Yen
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  ABSTRACT: The Mars Exploration Rover Opportunity has spent more than 2 years exploring Meridiani Planum, traveling approximately 8 kilometers and detecting features that reveal ancient environmental conditions. These include well-developed festoon (trough) cross-lamination formed in flowing liquid water, strata with smaller and more abundant hematite-rich concretions than those seen previously, possible relict "hopper crystals" that might reflect the formation of halite, thick weathering rinds on rock surfaces, resistant fracture fills, and networks of polygonal fractures likely caused by dehydration of sulfate salts. Chemical variations with depth show that the siliciclastic fraction of outcrop rock has undergone substantial chemical alteration from a precursor basaltic composition. Observations from microscopic to orbital scales indicate that ancient Meridiani once had abundant acidic groundwater, arid and oxidizing surface conditions, and occasional liquid flow on the surface.
  Science 10/2006; 313(5792):1403-7. · 31.20 Impact Factor
• Source

  Available from: Christian Schröder

  Article: Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills

  R. E. Arvidson, S. W. Squyres, R. C. Anderson, J. F. Bell, D. Blaney, J. Brückner, N. A. Cabrol, W. M. Calvin, M. H. Carr, P. R. Christensen, [......], L. A. Soderblom, R. Sullivan, S. D. Thompson, N. J. Tosca, A. Wang, H. Wänke, J. Ward, T. Wdowiak, M. Wolff, A. Yen
  Journal of Geophysical Research 01/2006; · 3.02 Impact Factor
• Article: Overview of the Opportunity Mars Exploration Rover mission to Meridiani Planum: Eagle crater to Purgatory ripple

  S. W. Squyres, R. E. Arvidson, D. Bollen, J. F. Bell, J. Brückner, N. A. Cabrol, W. M. Calvin, M. H. Carr, P. R. Christensen, B. C. Clark, [......], M. Sims, M Smith, P Smith, L. A. Soderblom, R. Sullivan, N. J. Tosca, H. Wänke, T. Wdowiak, M. Wolff, A. Yen
  Journal of Geophysical Research 01/2006; · 3.02 Impact Factor
• Article: Overview of the Spirit Mars Exploration Rover Mission to Gusev Crater: Landing site to Backstay Rock in the Columbia Hills

  R. E. Arvidson, S. W. Squyres, R. C. Anderson, J. F. Bell, D. Blaney, J. Brückner, N. A. Cabrol, W. M. Calvin, M. H. Carr, P. R. Christensen, [......], L. A. Soderblom, R. Sullivan, S. D. Thompson, N. J. Tosca, A. Wang, H. Wanke, J. Ward, T. Wdowiak, M. Wolff, A. Yen
  Journal of Geophysical Research 01/2006; · 3.02 Impact Factor
• Source

  Available from: Christian Schröder

  Article: Overview of the Opportunity Mars Exploration Rover mission to Meridiani Planum: Eagle crater to Purgatory ripple

  S. W. Squyres, R. E. Arvidson, D. Bollen, J. F. Bell, J. Bruckner, N. A. Cabrol, W. M. Calvin, M. H. Carr, P. R. Christensen, B. C. Clark, [......], M. Sims, M Smith, P Smith, L. A. Soderblom, R. Sullivan, N. J. Tosca, H. Wanke, T. Wdowiak, M. Wolff, A. Yen
  Journal of Geophysical Research 01/2006; 111. · 3.02 Impact Factor
• Article: Provenance and diagenesis of impure evaporitic sedimentary rocks on Meridiani Planum, Mars

  S. M. McLennan, J. F. Bell III, W. M. Calvin, P. R. Christensen, B. C. Clark, P. A. de Souza, W. H. Farrand, D. Fike, R. Gellert, A. Ghosh, [......], Z. Learner, M. C. Malin, H. Y. McSween Jr, J. Pocock, S. W. Ruff, S. W. Squyres, N. J. Tosca, W. Watters, M. B. Wyatt, A. Yen
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  ABSTRACT: Impure evaporitic sedimentary rocks preserved on Meridiani Planum preserve textural, mineralogical and geochemical evidence for a protracted and complex history of syndepositional through burial diagenesis dominated by phreatic meteoric conditions.
  Lunar and Planetary Science XXXVI, Lunar and Planetary Institute (2005). 02/2005;
• Article: Results and Implications of Mineralogical Models for Chemical Sediments at Meridiani Planum

  B. C. Clark, S. M. McLennan, R. V. Morris, R. Gellert, B. L. Jolliff, A. H. Knoll, T. K. Lowenstein, D. W. Ming, N. J. Tosca, P. R. Christensen, A. S. Yen, J. Brückner, W. M. Calvin, W. H. Farrand, J. Zipfel, S. Gorevan, S. W. Squyres
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  ABSTRACT: Outcrops of salt-rich silicic sediments at Meridiani Planum were analyzed using sample preparation via grinding to reveal rock interiors. X-ray fluorescence and Moessbauer analysis are combined with IR spectroscopy to infer mineral composition.
  02/2005; 36:1446.
• Article: Seeing the Soils of Meridiani Planum Through the Eyes of Pancam and Microscopic Imager

  C. M. Weitz, R. C. Anderson, Bell, J. F., III, N. A. Cabrol, W. M. Calvin, B. L. Ehlmann, W. H. Farrand, R. Greeley, K. E. Herkenhoff, J. R. Johnson, B. L. Jolliff, R. V. Morris, L. A. Soderblom, S. W. Squyres, R. J. Sullivan
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  ABSTRACT: We are using data from the Pancam and Microscopic Imager (MI) on the Opportunity rover to characterize soil grains at Meridiani Planum greater than 0.3 mm in size. In general, the size of most grains within Eagle crater falls between 1.5-3.5 mm, and they are very circular in cross section.
  02/2005; 36:1362.
• Article: Seeing the Soils of Meridiani Planum Through the Eyes of Pancam and Microscopic Imager

  C. M. Weitz, R. C. Anderson, Bell, J. F, III, N. A. Cabrol, W. M. Calvin, B. L. Ehlmann, W. H. Farrand, R. Greeley, K. E. Herkenhoff, J R Johnson
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  ABSTRACT: We are using data from the Pancam and Microscopic Imager (MI) on the Opportunity rover to characterize the soil grains at Meridiani Planum. We have traced individual grains in all MI images of the soils using the software application ImageJ distributed by NIH, and subsequently derived size and shape properties about the grains. The resolution of the MI is 31 microns per pixel [1] so we limit our measurements to those grains larger than about 0.3 mm in size. In cases where the grain is partially or substantially buried by other grains or finer soil particles, we do not make a measurement. False-color composites from Pancam images that cover the same location imaged by MI are made from the Left 2,5,6 (753, 535, 482 nm) filters or Right 2,7,1 (753, 1009, 430 nm) filters [2] in the Red, Green, and Blue channels, respectively. These color images are then merged with the MI images to illustrate color properties of particular grains. Pancam spectra are also extracted from grains when there is sufficient spatial coverage. in diameter. Figure 2 illustrates the dominance of these small grains at this particular location, which happens to be on the southern wall of Eagle crater. The Pancam color merge with this MI image suggests that the small spherules are more consistent with the basalt grains than the blueberries (spherulitic concretions derived from outcrop rocks [7]). The resolution of Pancam images of this location is on the order of 0.5 mm so the grains are only barely resolved. A Mossbauer measurement taken on an adjacent soil (Sol 53 Vanilla) that is composed solely of these smaller spherules (Fig 1) is consistent with a basaltic composition for the grains. Their concentration at this particular location in a brighter, elongate patch along the southeastern wall compared to elsewhere inside Eagle crater suggests wind activity favored their transport and subsequent deposition here. Their spherical shape is also possibly the result of wind action rounding them during transport, though water action cannot be ruled out.
  Lunar and Planetary Science Conference Proceed. 02/2005;
• Article: Mineral Composition and Abundance of the Rocks and Soils at Gusev and Meridiani from the Mars Exploration Rover Mini-TES Instruments

  P. R. Christensen, M. B. Wyatt, T. D. Glotch, A D Rogers, S Anwar, R. E. Arvidson, J. L. Bandfield, D. L. Blaney, C Budney, W. M. Calvin
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  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) has provided remote measurements of mineralogy, thermophysical properties, and atmospheric temperature profile and composition of the outcrops, rocks, spherules, and soils surrounding the Spirit and Opportunity Rovers. The mineralogy of volcanic rocks provides insights into the composition of the source regions and the nature of martian igneous processes. Carbonates, sulfates, evaporites, and oxides provide information on the role of water in the surface evolution. Oxides, such as crystalline hematite, provide insight into aqueous weathering processes, as would the occurrence of clay minerals and other weathering products. Diurnal temperature measurements can be used to determine particle size and search for the effects of sub-surface layering, which in turn provide clues to the origin of surficial materials through rock disintegration, aeolian transport, atmospheric fallout, or induration. In addition to studying the surface properties, Mini-TES spectra have also been used to determine the temperature profile in the lower boundary layer, providing evidence for convective activity, and have determined the seasonal trends in atmospheric temperature and dust and cloud opacity.
  02/2005;
• Conference Proceeding: Seeing the soils of Meridiani Planum through the eyes of Pancam and Microscopic Imager.

  Weitz, C. M, R. C. Anderson, J. F. Bell, N. A. Cabrol, W. M. Calvin, B. L. Ehlmann, W. H. Farrand, R. Greeley, K. E. Herkenhoff, B. L. Jolliff, R. V. Morris, L. A. Soderblom, S. W. Squyres, and R. J. Sullivan
  36th LPSC; 01/2005
• Article: Mineralogy at Meridiani Planum from the Mini-TES Experiment on the Opportunity Rover.

  P R Christensen, M B Wyatt, T D Glotch, A D Rogers, S Anwar, R E Arvidson, J L Bandfield, D L Blaney, C Budney, W M Calvin, [......], A T Knudson, H Y McSween, G L Mehall, L K Mehall, J E Moersch, R V Morris, M D Smith, S W Squyres, S W Ruff, M J Wolff
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  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Opportunity investigated the mineral abundances and compositions of outcrops, rocks, and soils at Meridiani Planum. Coarse crystalline hematite and olivine-rich basaltic sands were observed as predicted from orbital TES spectroscopy. Outcrops of aqueous origin are composed of 15 to 35% by volume magnesium and calcium sulfates [a high-silica component modeled as a combination of glass, feldspar, and sheet silicates (approximately 20 to 30%)], and hematite; only minor jarosite is identified in Mini-TES spectra. Mini-TES spectra show only a hematite signature in the millimeter-sized spherules. Basaltic materials have more plagioclase than pyroxene, contain olivine, and are similar in inferred mineral composition to basalt mapped from orbit. Bounce rock is dominated by clinopyroxene and is close in inferred mineral composition to the basaltic martian meteorites. Bright wind streak material matches global dust. Waterlain rocks covered by unaltered basaltic sands suggest a change from an aqueous environment to one dominated by physical weathering.
  Science 01/2005; 306(5702):1733-9. · 31.20 Impact Factor
• Source

  Available from: Deanne Rogers

  Article: Initial results from the Mini-TES experiment in Gusev Crater from the Spirit Rover.

  P R Christensen, S W Ruff, R L Fergason, A T Knudson, S Anwar, R E Arvidson, J L Bandfield, D L Blaney, C Budney, W M Calvin, [......], H Y McSween, G L Mehall, L K Mehall, J E Moersch, R V Morris, A D Rogers, M D Smith, S W Squyres, M J Wolff, M B Wyatt
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  ABSTRACT: The Miniature Thermal Emission Spectrometer (Mini-TES) on Spirit has studied the mineralogy and thermophysical properties at Gusev crater. Undisturbed soil spectra show evidence for minor carbonates and bound water. Rocks are olivinerich basalts with varying degrees of dust and other coatings. Dark-toned soils observed on disturbed surfaces may be derived from rocks and have derived mineralogy (+/-5 to 10%) of 45% pyroxene (20% Ca-rich pyroxene and 25% pigeonite), 40% sodic to intermediate plagioclase, and 15% olivine (forsterite 45% +/-5 to 10). Two spectrally distinct coatings are observed on rocks, a possible indicator of the interaction of water, rock, and airfall dust. Diurnal temperature data indicate particle sizes from 40 to 80 microm in hollows to approximately 0.5 to 3 mm in soils.
  Science 09/2004; 305(5685):837-42. · 31.20 Impact Factor
• Article: Mars Exploration Rover Panoramic Camera Multidimensional Analyses and Surface Spectral Variability

  Seelos, F. P., IV, J. M. Soderblom, W. H. Farrand, J. R. Johnson, J. N. Sohl-Dickstein, Bell, J. F., III, S. W. Squyres, R. E. Arvidson, R. V. Morris, H. Y. McSween, W. M. Calvin, D. L. Blaney, Athena Science Team
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  ABSTRACT: The spectral variability of the martian surface at the Spirit and Opportunity landing sites is explored through the multidimensional analysis of Mars Exploration Rover (MER) Panoramic Camera (Pancam) multispectral image data.
  02/2004; 35:2166.
• Source

  Available from: Jeffrey R. Barnes

  Article: The state and future of Mars polar science and exploration.

  S M Clifford, D Crisp, D A Fisher, K E Herkenhoff, S E Smrekar, P C Thomas, D D Wynn-Williams, R W Zurek, J R Barnes, B G Bills, [......], B C Clark, G D Clow, J A Cutts, D Dahl-Jensen, W B Durham, F P Fanale, J D Farmer, F Forget, K Gotto-Azuma, H J Zwally
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  ABSTRACT: As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of approximately 10(6) km2 and total as much as 3-4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young--preserving a record of the seasonal and climatic cycling of atmospheric CO2, H2O, and dust over the past approximately 10(5)-10(8) years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet--documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason--providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding.
  Icarus 05/2000; 144(2):210-42. · 3.38 Impact Factor
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  Available from: caltech.edu

  Article: Evidence for crystalline water and ammonia ices on Pluto's satellite charon.

  M E Brown, W M Calvin
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  ABSTRACT: Observations have resolved the satellite Charon from its parent planet Pluto, giving separate spectra of the two objects from 1.0 to 2.5 micrometers. The spectrum of Charon is found to be different from that of Pluto, with water ice in crystalline form covering most of the surface of the satellite. In addition, an absorption feature in Charon's spectrum suggests the presence of ammonia ices. Ammonia ice-water ice mixtures have been proposed as the cause of flowlike features observed on the surfaces of many icy satellites. The existence of such ices on Charon may indicate geological activity in the satellite's past.
  Science 01/2000; 287(5450):107-9. · 31.20 Impact Factor