Planetary science: Multiple data sets, multiple scales, and unlocking the third dimension

Paula Martin* Department of Earth Sciences, Durham University, Science Laboratories, Road, Durham DH1 3LE, UK Ellen R. Stofan* Proxeny Research, 20528 Farcroft Lane, Laytonsville, Maryland 20882, USA

ABSTRACT ogy. The experience gained at will help obtain images or analyze samples at distances us to plan and exploit the 3-D exploration of of up to several meters. Remotely sensed data Observations of the planets in our solar other planets in the future. encompass all the data collected by spacecraft in system cover a wide range of scales and are orbit around a planet, or as a spacecraft fl ies-by undertaken using a variety of techniques Keywords: planetary, Mars, surface, subsur- a planet en route to another location. In general, and platforms, resulting in extremely rich face. in-situ data provide highly detailed information data sets. This review paper provides a basic about a location that is somewhat limited in introduction to the available range of plan- INTRODUCTION size, whereas remotely sensed data provide less etary science data sets, and the combination detailed information about a location that cov- of these data sets over a range of scales, reso- Planetary science provides a basis from ers a much wider area (often >90% of an entire lutions, and techniques to address geological which to consider the formation and evolution planetary surface). In-situ data provide “ground problems. The wealth of data available and of Earth in a wider context. It can be used as truth,” which is then used to expand the interpre- the use of a selected combination of data sets a prompt to reconsider the bigger picture, and tation of remotely sensed data sets. to address geological problems are best illus- ask fundamental questions such as: Why does All of the data from NASA planetary missions trated by taking a closer look at the planet plate tectonics occur only on Earth, and not on can be accessed through the NASA Planetary Mars. As a result of the increasing preci- other planets? In the absence of plate tectonics, Data System (PDS) (for more information, see sion of spacecraft sensors, we now have data how do other planets lose their heat? What are http://pds.jpl.nasa.gov/), or by contacting your sets that cover the whole planet at spatial the major mechanisms for planetary resurfac- local NASA Regional Planetary Image Facility resolutions ranging from kilometers down ing? What geological processes operate on each (RPIF) (for more information, see http://www. to meters (e.g., ) and planet (and how and when do they operate)? lpi.usra.edu/library/RPIF/). All of the data multiple wavelengths (e.g., Mars Reconnais- The data available to us to try to address these from ESA planetary missions can be accessed sance Orbiter), which have been collected questions can be divided into two distinct types: through the ESA Planetary Science Archive over several years. This global coverage is in-situ data and remotely sensed data. In-situ (PSA) (for more information, see http://www. complemented by surface missions that pro- data encompass all the data from the Apollo mis- rssd.esa.int/index.php?project = PSA). Data vide localized data sets down to microscopic sions to the moon, and all other data collected from each mission are made available follow- resolutions (Mars Exploration Rovers). Thus, by instruments located on the surface of planets, ing a proprietary period, which varies in length it is now possible to study geological features including both stationary landers and rovers. for each mission (but is typically a number and processes quantitatively over an impres- It should be noted that not all in-situ data are of months following initial acquisition of the sive range of scales. The combination of new obtained by instruments strictly in physical con- data), during which time the data are processed data sets from current and future missions to tact with the planetary surface. For example, all and analyzed by the team of mission scien- Mars (e.g., Mars Express and Mars Recon- imaging and geochemical instruments on board tists. Updates to the available data are made naissance Orbiter) will facilitate attempts to stationary landers and rovers are generally con- on a regular (e.g., monthly or quarterly) basis, unlock the third dimension of geol- sidered to be in-situ instruments, even those that following the proprietary period, to facilitate

*[email protected]; [email protected].

Geosphere; December 2007; v. 3; no. 6; p. 435–455; doi: 10.1130/GES00089.1; 18 fi gures.

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further analysis and interpretation. The total Surveyor Missions (1990s). Each of the space- missions over the past 30 yr. The Viking orbit- planetary data archive is vast; for example, the craft, landers, and rovers used in these missions ers, in the 1970s, provided grayscale images data archive for the Thermal Emission Imaging carries a wide-ranging suite of scientifi c instru- of the at resolutions of 150 to System (THEMIS) instrument, which is just ments, including high-resolution imagers and 300 m per pixel (e.g., Fig. 1), dependent on the one of three major instruments on board the spectrometers, instruments used to identify the elevation of the spacecraft above the Martian Mars Odyssey spacecraft, is expected to grow to physical properties of the planetary surface such surface (e.g., Snyder and Moroz, 1992). More approximately 6 TB. as thermal emission and topography, and instru- recently, the Mars Orbital Camera (MOC) In this review paper, we will use the explora- ments used to investigate the geophysical prop- instrument, on board the Mars Global Surveyor tion of the planet Mars to provide examples of erties of the planet as a whole, such as gravity (MGS) spacecraft, was designed to routinely the range of planetary data that is available, the and magnetic fi elds. More recently, spacecraft acquire images at three different, complemen- range of instruments used in planetary explora- have also begun to include radar sounders to tary resolutions, using a limited number of color tion, and the range of scales that these instru- penetrate the planetary surface and attempt to fi lters: (1) global images, typically at a resolu- ments cover. We will discuss the use of plan- identify the properties of the subsurface. More tion of 7.5 km per pixel; (2) wide-angle, context etary data sets to develop our understanding of information about the different types of scien- images, typically at a resolution of 240 m per planetary surfaces and possible ways of access- tifi c instrumentation used in Mars Exploration is pixel, using red and blue fi lters; and (3) narrow- ing the third dimension on a planetary scale. available through the NASA Mars Exploration angle, high-resolution images, typically at a Web site: http://mars.jpl.nasa.gov/. resolution of 1.5 to 12 m per pixel (e.g., Fig. 2) OVERVIEW OF MARS EXPLORATION (Albee et al., 1998). Following the huge success MARS IMAGE AND COMPOSITIONAL of the MOC instrument, the Mars Reconnais- There are three spacecraft currently in orbit DATA sance Orbiter (MRO) spacecraft carries three around Mars acquiring and returning data to separate imaging instruments that operate over Earth: Mars Odyssey (2001), Mars Express The wide variety of spacecraft, landers, and a range of scales comparable with those cov- (2003) and Mars Reconnaissance Orbiter rovers involved in Mars exploration and their ered by MOC and incorporate a wider range (2006), in addition to the two Mars Explora- associated instrumentation allow us to investi- of color options (Zurek and Smrekar, 2007). tion Rovers (2003), Spirit and Opportunity, that gate the Martian surface over a wide range of Firstly, the Mars Color Imager (MARCI) takes are currently exploring the Martian surface. scales, covering many orders of magnitude. global images at fi ve visible and two ultravio- These current missions continue to acquire The rich diversity of the available data can be let wavelengths, typically at a resolution of 1 data that complement that acquired by previ- illustrated by considering the range of resolu- to 10 km per pixel (e.g., Fig. 3). Secondly, the ous missions such as Viking (1970s), and the tions, and the range of wavelengths, of imaging Context Camera (CTX) takes grayscale images, more recent Mars Pathfi nder and Mars Global instruments used by a selection of the various typically at resolutions of 6 m per pixel (e.g.,

Figure 1. Viking Orbiter 1 image of Meridiani Planum. The red and yellow ellipses indicate the designated landing site for the Mars Explo- ration Rover, Opportunity. The ellipses are ~71 km long; north is up. Image credit: NASA/JPL.

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Figure 2. Pair of Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) narrow-angle images showing the landing site of the , Opportunity, in Meridiani Planum, before and after the landing. The fi rst (top) image was acquired on 24 August 2003, fi ve months prior to the 25 January 2004 landing. The second (bottom) image was acquired on 1 February 2004, and shows Opportunity located within an ~20–m–diameter crater. In both images north is up; the second (bottom) image is ~1.4 km wide. The dark area on the right side of the upper picture was not imaged by MOC until after the landing. Image credit: NASA/JPL/MSSS.

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Figure 3. Mars Reconnaissance Orbiter (MRO) Mars Color Imager (MARCI) composite mosaic of four images of the north polar cap of Mars. This mosaic was generated from three color channels, centered on wavelengths of 425 nm, 550 nm, and 600 nm, and shows the region poleward of ~72° N lat. The white area is the perennial north polar cap, which is mostly water ice, sitting on top of the pale-brown, north-polar, layered materials. The dark areas are circumpolar dunes. Image credit: NASA/JPL/MSSS.

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Fig. 4), making observations simultaneously with the high-resolution images taken by the High Resolution Imaging Science Experiment (HiRISE). Finally, HiRISE operates at vis- ible and near-infrared wavelengths and takes both panchromatic and color images, typi- cally at resolutions of tens of centimeters per pixel (e.g., Fig. 5) (McEwen et al., 2007). The global coverage provided by orbiting space- craft described above is complemented by in- situ images obtained by landers and rovers at resolutions ranging from a few centimeters per pixel to tens of microns per pixel. For example, the versatile Panoramic Cameras on the Mars Exploration Rovers, Spirit and Opportunity, can take long-range images typically at resolutions of 2.8 cm per pixel at a range of 100 m through to short-range images at much higher resolu- tions, while the Microscopic Imagers (MI), also on the Mars Exploration Rovers, take images typically at a resolution of 30 microns per pixel (e.g., Fig. 6) (Bell et al., 2003; Herkenhoff et al., 2004; Squyres et al., 2004a, 2004b). Thus, it is now possible to study geological features and processes on Mars over an impressive range of scales. The Thermal Emission Spectrometer (TES) on board MGS measured the thermal infrared energy (heat) emitted from Mars, which can be used to constrain both the geology and the . In total, TES collected over 206 million spectra. It made several important discoveries, the most infl uential of which was the discovery of hematite in Meridiani Planum (Christensen et al., 2001), a key contribution to NASA’s decision to send the Opportunity rover to this region (e.g., Fig. 7). The Thermal Emis- sion Imaging System (THEMIS) on board Mars Odyssey is a multi-wavelength camera, operat- ing in fi ve visual bands and ten infrared bands, that combines both thermal emission and imag- ing techniques. THEMIS is designed to fur-

Figure 4. Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) image of , one of the oldest valleys on Mars. The image is centered near 25.6° N, 19.4° W, and is ~1.2 km wide; north is up. Mawrth Vallis was formed in and subse- quently covered by layered rocks, from which it is now being exhumed. This area is of particular interest because of the pres- ence of clay minerals, fi rst observed by the OMEGA instrument on board Mars Express (see Fig. 10). This area has now also been observed by the CRISM instrument on board MRO (see Fig. 9). Image credit: NASA/JPL/MSSS.

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Figure 5. Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) image of Victoria cra- ter and the Mars Exploration Rover, Opportunity, in Meridiani Planum. This is an enhanced-color view generated from images acquired by HiRISE using two of its color fi lters: red and blue-green. Victoria crater is ~800 m in diameter; north is up. Image credit: NASA/JPL/University of Arizona.

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Figure 6. Mars Exploration Rover, Opportunity, images of the Martian rock named “Last Chance.” (A) Small portion of Opportunity’s Panoramic Camera image showing “Last Chance” in context, within an outcrop near the Opportunity landing site. The two vertical cracks in the rock may be used to locate the Microscopic Imager (MI) image shown in (B). Image Credit: NASA/JPL/Cornell. (B) Microscopic Imager (MI) image of the lower portion of “Last Chance,” showing a close-up of texture interpreted as cross-lamination evidence that sediments forming the rock were laid down in fl owing water. The two vertical cracks in the rock at the top of this image may be used to locate it within the Panoramic Camera image shown in (A). In the central part of the image, the cross-lamination suggests that the water that created these features was fl owing from left to right. Interpretive black lines trace the cross-laminae; interpretive blue lines indicate boundaries of possible sets of cross-laminae. Image Credit: NASA/JPL/Cornell/ARC.

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Figure 7. Mars Global Surveyor (MGS) Thermal Emission Spectrometer (TES) and Mars Odyssey Thermal Emission Imag- ing Spectrometer (THEMIS) composite image showing the abundance and location of hematite at the Mars Exploration Rover Opportunity’s landing site, in Meridiani Planum. The background surface image of Meridiani Planum is a mosaic of daytime infrared images acquired by THEMIS, superimposed on which is a rainbow-colored map showing the abundance and location of hematite, as observed by TES. Red and yellow indicates higher concentrations of hematite, whereas green and blue areas indicate lower concentrations. The black ellipse indicates the designated landing site for the Mars Explora- tion Rover, Opportunity. The ellipse is ~71 km long; north is up. Image Credit: NASA/JPL/ASU.

ther our understanding of Martian geology by ing liquid water. In contrast, the landing site for Christensen et al., 2004). Thus, Mini-TES has detecting any rocks that have been altered by Spirit, crater, is an enclosed, low-lying been used to provide further “ground truth” for water, and any “hot spots” that may indicate the area with a channel produced by fl owing liq- TES, THEMIS and other instruments. presence of subsurface hydrothermal systems. uid water running straight into it. Both Spirit The Compact Reconnaissance Imaging Spec- THEMIS has also made several important dis- and Opportunity have greatly enhanced our trometer for Mars (CRISM), on board MRO, coveries, including confi rming the presence of understanding of the Martian surface, through is the most recent instrument to arrive at Mars hematite in Meridiani Planum and mapping detailed analyses of their landing sites, and designed to determine the surface mineralogy its extent in greater detail (Christensen et al., by enhancing our ability to interpret global and hence identify traces of past and present 2005), thus validating NASA’s choice of the data sets (Squyres et al., 2004a; 2004b; 2006; water on the surface of Mars. CRISM spans region as the landing site for Opportunity. Arvidson et al., 2006). For example, in addi- both visible and infrared wavelengths, specifi - The landing sites for both Spirit and Oppor- tion to many other instruments, both Spirit and cally from 362 to 3920 nm, and is able to scan tunity were chosen because they both showed Opportunity carry a Miniature Thermal Emis- through these wavelengths at 6.55 nm per chan- clear but contrasting evidence for the presence sion Spectrometer (Mini-TES). As the name nel, covering the Martian surface at typical spa- of liquid water at their respective locations in suggests, Mini-TES is a miniaturized version tial resolutions of tens of meters (e.g., Fig. 9). the past. Hematite is considered to be a chemical of TES, and similarly collects high-resolution The fi rst results from CRISM are currently being signature for the presence of past water because infrared spectra that help to identify the miner- received and analyzed (e.g., Murchie et al., it is usually produced in an environment includ- alogy of the Martian surface (e.g., Fig. 8) (e.g., 2006; 2007; Pelkey et al., 2007). Many of these

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results were presented at the 38th annual Lunar orbit, all located close to the top of the section. and Planetary Science Conference, including Unsurprisingly, the materials exposed across the the initial components of a global multispectral region are more diverse than those observed in survey, targeted observations of regions rich the ~7 m of section explored by Opportunity. in sulfates and phyllosilicates, the north polar The light-toned, layered rocks observed in Sinus cap, and monitoring of seasonal variations (see Meridiani are not unique to this region. Across http://www.lpi.usra.edu/meetings/lpsc2007/pdf/ the region, former valleys and impact craters are sess323.pdf). interbedded with the exposed rocks, and burial Compositional data gathered by NASA mis- and exhumation of paleosurfaces are observed, sions are complemented by those gathered by confi rming the presence of unconformities in the Observatoire pour la Minéralogie, l’Eau, les the rock record. Differences between the mate- Glaces, et l’Activité (OMEGA) investigation, on rials deposited inside impact craters and those board ESA’s Mars Express mission. OMEGA deposited in the surrounding area indicate that by the navigation camera in Meridiani is designed to map the surface composition of different depositional environments existed in Mars, typically at a resolution of 0.3 to 5 km per close proximity. pixel, using a series of 352 contiguous spectral The work of Edgett (2005) illustrates that the channels spanning both visible and near-infra- light-toned, layered rocks of the Sinus Meridi- red wavelengths (e.g., Fig. 10)(Bibring et al., ani region are sedimentary in nature, and are 2005). OMEGA data illustrate the diversity and comparable with the sedimentary rocks of the complexity of Martian surface mineralogy at Colorado Plateau in terms of the area covered the ~km scale, developing our understanding of and the diversity of erosional features, rela- both the mineralogical and aqueous evolution of tive albedo, and bedding styles. In addition to Mars, for example, through the identifi cation of the rocks exposed in , similar the alteration of some parts of the most ancient rocks have been observed in two other regions Martian terrains to clays (Bibring et al., 2005; of Mars (e.g., Figures 4, 9, and 10)—Mawrth Bibring et al., 2006). Vallis and the plains cut by the Valles Marin- eris—suggesting that conditions for the depo- Case Study: Integration of Data over a sition, lithifi cation, and diagenesis of sedimen- Range of Scales/Sinus Meridiani tary materials may have been present on Mars oor of the crater and in the crater outcrop have much lower hematite concentrations have much lower outcrop and in the crater of the crater oor in a variety of locations at a variety of times The integration of planetary data from a (Edgett, 2005). variety of missions over a range of scales can provide important insights into the formation MARS 3-D DATA SETS and evolution of surface features. For example, Edgett (2005) used data from the MGS and Mars To gain a deeper understanding of the geol- Odyssey missions, supplemented with data from ogy of Mars, more three-dimensional informa- Opportunity, , Viking 1, Viking 2, and tion about Mars is needed. To prove that sur- 2, to investigate the light-toned, layered face features result from the action of water, to rocks of the Sinus Meridiani region (e.g., Fig- determine how much water was involved in the ures 1, 2, 5, 6, 7, 8, and 11). Although these rocks process, and when the surface features formed, had been studied previously (e.g., Edgett and the 3-D shape of the surface feature in question Parker, 1997; Christensen et al., 2000; Edgett is needed. 3-D information can also be used and Malin, 2002; Hynek et al., 2002; Arvidson to identify landing sites for future missions. ve locations the rover visited along the Meridiani Planum rock outcrop. The bright red area behind the rover-lander has one behind the rover-lander area The bright red outcrop. visited along the Meridiani Planum rock ve locations the rover et al., 2003; Newsom et al., 2003; Christensen Firstly, it helps us to identify sites that are and Ruff, 2004; Christensen et al., 2004; Hynek, inappropriately dangerous places to try to land 2004; Ormo et al., 2004), Edgett (2005) used a because of sharp topography or large numbers combination of data from a variety of missions of boulders. Secondly, it helps us to understand over a range of scales to develop a better overall interactions between the surface and the atmo- understanding of these rocks, thus providing a sphere, which have a signifi cant impact on the framework for the geology of the Sinus Meridi- balloons and parachutes that are used to ensure ani region that may be used to more readily relatively safe landings. Finally, in combina- understand the results of future fi eld studies of tion with data from other instruments such as the area in a wider context. MOC on board MGS, it also helps us to iden- The framework laid out by Edgett (2005) is tify places that are most appropriate to con- based on a series of simple, but fundamental, tinue the search for , e.g., where observations. The total stratigraphic section there is recent geologic activity (Malin et al., observed in the Sinus Meridiani region from 2006; Okubo and McEwen, 2007; Crown et al. orbit is more than 800 m thick. The Opportunity 2007), or where there may possibly be a frozen rover has explored a total of ~7 m thickness, sea (Murray et al., 2005; Balme et al., 2007; less than 1% of the total section observed from Jaeger et al., 2007). Figure 8. Mars Exploration Rover, Opportunity, Mini Thermal Emission Spectrometer (Mini-TES) data superimposed on images taken Thermal Emission Spectrometer Mini Opportunity, Figure 8. Mars Exploration Rover, collected at fi These Mini-TES data were Planum. on the fl the areas However, of the highest hematite concentrations observed in this crater. NASA/JPL/Cornell/ASU. plains. Image Credit: than those found on the surrounding

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Figure 9. Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) images of the area directly south of Mawrth Vallis. The images were taken in 544 colors covering a wavelength range of 362 to 3920 nm. Each image covers an area ~13 km long and, at the narrowest point, ~9 km wide. The images are four renderings of the same data set. The image on the top left is an approximately true-color representation; the image on the top right is false color, showing brightness of the surface at selected infrared wavelengths; the image on the bottom left shows areas high in iron-rich clay, and the bottom right image shows areas high in aluminum-rich clay. Image Credit: NASA/JPL/JHUAPL/Brown University.

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Figure 10. Mars Express (MEX) Observatoire pour la Minéralogie, l’Eau, les Glaces, et l’Activité (OMEGA) map of water-rich (clay) minerals in the Mawrth Vallis area. The blue areas indicate the presence of clay minerals, as observed by OMEGA, superimposed on a grayscale High Resolution Stereo Camera (HRSC) 3-D perspective view. Image Credit: ESA/OMEGA/HRSC.

We have a high-resolution topography data cover ~80% of Earth’s land surface (most of total volume of the north polar ice cap and set for Mars, acquired through the Mars Orbiter the land surfaces that lay between 60° N lat the seasonal variations in its morphology and Laser Altimeter (MOLA) instrument on board and 54° S lat), and have been used to produce extent, which provide important constraints MGS (e.g., Fig. 12) (Smith et al., 2001). The standard DEMs for these regions of Earth that on estimates of the present-day abundance of MOLA data have been converted to both grid- have a maximum horizontal resolution of 30 m. . Zuber et al. (1998) also used ded and spherical harmonic models for the The absolute horizontal and vertical accuracy the MOLA data to study a variety of geologi- topography and shape of Mars that have verti- of SRTM data is 20 m and 16 m, respectively cal features in the north polar region, including cal and radial accuracies of ~1 m with respect (Gesch et al., 2006). layered terrain, troughs and chasms, and impact to the planet’s center of mass. The MOLA The MOLA data set has been used to signifi - craters, thus providing new insights into their global topographic grid has a maximum spa- cantly improve our understanding of Mars. For formation and evolution. tial resolution of 0.0039° x 0.0039° (0.23 × example, MOLA data have been used to ana- Use of the MOLA data set has also resulted 0.23 km2 at the equator). The absolute hori- lyze the north polar ice cap on Mars (Fig. 13), in a new understanding of the relative age of the zontal and vertical accuracy of MOLA data which is one of the largest currently identifi ed Martian surface, which is critical for models is on the order of 1 m and 300 m, respectively reservoirs of volatiles on the planet, and has a of the formation of the Martian crustal hemi- (Smith et al., 1999a) major impact on geological processes in the spheric dichotomy. Prior to the MGS mission, MOLA data are comparable with the Shut- local polar region and on the seasonal and cli- the northern lowlands of Mars were interpreted tle Radar Topography Mission (SRTM) data matic evolution of the planet as a whole. Zuber to be relatively younger than the southern high- set for Earth (Gesch et al., 2006). SRTM data et al. (1998) used MOLA data to calculate the lands, because of the apparent lack of signifi -

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Figure 11. Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image of the sedimentary rock outcrops in northern Meridiani Planum, showing a diverse range of physical properties and erosional characteristics. The image is located near 1.2° N, 1.1° E, northeast of the Opportunity landing site, and covers an area ~3 km across. Image Credit: NASA/JPL/MSSS.

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Figure 12. Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) global false-color topography of Mars. These images are orthographic projections that contain over 200,000,000 points and ~5,000,000 altimetric crossovers. The spatial resolution is ~15 km at the equator and less at higher latitudes; the vertical accuracy is <5 m. In the image on the left, the feature in red and white is the Rise. In the image on the right, the purple circular area is the Hellas impact basin. Image Credit: NASA/JPL/GSFC/MOLA.

cant numbers of impact craters in the northern presented at the 38th annual Lunar and Plane- tian geology in 3-D. However, the instruments hemisphere. However, a population of impact tary Science Conference, including studies of used in these studies can only access the rocks craters (Head et al., 2002), and subdued quasi- volcanic and tectonic landforms and observa- exposed at the surface. For example, the total circular depressions that are interpreted to be tions of specifi cally targeted regions (see e.g., vertical section exposed in the Sinus Meridi- ancient impact craters and basins that have http://www.lpi.usra.edu/meetings/lpsc2007/ ani region is less than 900 m. In the next sec- been buried by subsequent resurfacing (Frey et pdf/sess322.pdf). The HSRC is designed to tion of this paper, we look at instruments that al., 2002), have been identifi ed in the northern acquire multispectral stereo images of the are designed to probe the subsurface. lowlands of Mars using MOLA data, indicat- Martian surface to support the study of a ing that the northern lowlands are much older variety of surface processes including volca- WHAT ABOUT THE SUBSURFACE? than previously thought (e.g., Fig. 14). The nism, tectonism, impact cratering, erosion, northern and southern hemispheres of Mars and deposition (e.g., Fig. 10). HRSC context The fi rst instrument to produce a global are now thought to have relatively similar ages, images typically have spatial resolution of data set of observations of the near subsurface constraining the formation of the hemispheric tens of meters, whereas the additional Super of Mars, to depth of tens of centimeters, is the dichotomy to early Martian history. Resolution Channel (SRC) images embed- Gamma Ray Spectrometer (GRS) on board Both MRO and the Mars Express (MEX) ded within the context images have typical Mars Odyssey (Boynton et al., 2004; Evans et mission, currently in Mars orbit, are address- spatial resolutions of only 2 or 3 m, enabling al., 2006). The GRS global data set provides ing the need for more 3-D image data directly us to develop detailed understanding of information on the spatial distribution of ele- through the production of stereo images and Martian surface processes in 3-D (Neukum mental abundances, which have been used to DEMs from HiRISE data, and the High Reso- et al., 2004). further our understanding of the bulk composi- lution Stereo Camera (HRSC) on board MEX. Recent studies (e.g., Edgett, 2005; Malin tion and early differentiation, crustal and atmo- Many of the initial results from HiRISE were et al., 2006) do successfully investigate Mar- spheric evolution of Mars (e.g., Newsom et al.,

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Figure 13. Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) 3-D image of the north polar region of Mars. To create this model, ~2.6 million data points were assembled into a topographic grid of the north pole with a spatial resolution of 1 km and a vertical accuracy 5 to 30 m. This model was used to estimate the volume of its water ice cap with unprecedented precision (Zuber et al., 1998). Image Credit: NASA/JPL/GSFC/MOLA.

2007; Taylor et al., 2006; Sprague et al., 2007). is abundant evidence that liquid water was A buried impact basin that is potentially Thus, the GRS data span the gap between the once present on the surface of Mars, but we partially fi lled with ice was also identifi ed wide variety of data sets produced by instru- don’t know where the water is now. Some (Picardi et al., 2005). More recently, the ments designed to investigate the surface and water may have escaped the planet along with detection of a large number of buried impact those that are designed to investigate the deep the majority of the Martian atmosphere, but craters in the northern hemisphere of Mars by subsurface of Mars. the rest may still be trapped in the subsurface MARSIS confi rms that the crust beneath the To access the deep subsurface, instruments in solid or liquid form. MARSIS is mapping plains is similar in age to the Martian south- need to use techniques that can penetrate to the subsurface structure to a depth of a few ern highlands, placing constraints on models depths of several kilometers. Currently, the kilometers, using low-frequency radio waves of the origin of the Martian crustal dichotomy most appropriate technique is sounding radar. that are refl ected by any subsurface contacts (Fig. 14) (Watters et al., 2006). SHARAD is There are two radar instruments currently between layers with different dielectric prop- mapping the subsurface structure at shallower operating in Mars orbit: the Mars Advanced erties, enabling us to distinguish between depths than MARSIS (Seu et al., 2004; 2007). Radar for Subsurface and Ionospheric Sound- layers of different materials that may be pres- Preliminary analysis of early results from ing (MARSIS) instrument on board MEX and ent, including water and ice (Picardi et al., SHARAD is also focused on the north polar the Shallow Subsurface Radar (SHARAD) 2005). Early results from MARSIS include layered deposits (Phillips et al., 2007). Given instrument on board MRO. Both MARSIS the investigation of the north polar layered the possible identifi cation of deposits formed and SHARAD are designed to answer one of deposits, indicating that these deposits cover recently by water on Mars (Malin et al., 2006), the fundamental questions about the history a total thickness of 1.8 km, and that they are SHARAD may provide exciting results. of Mars: Where did all the water go? There composed of nearly pure water ice (Fig. 15).

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Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/435/854324/i1553-040X-3-6-435.pdf by guest on 01 October 2021 Planetary science obal Surveyor (MGS) Mars Orbiter (MGS) Mars Orbiter obal Surveyor ecember 2006. ecember than 200 km detected by MOLA (plotted in white) than 200 km detected by MOLA and those of buried basins detected by MARSIS (plotted in black). White polygons show the area covered by MARSIS orbits as of D covered White polygons show the area and those of buried basins detected by MARSIS (plotted in black). Figure 14. Mars Express (MEX) Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) data superimposed on Mars Gl for Advanced Radar (MEX) Mars 14. Mars Express Figure larger topographic depressions This image indicates the locations and diameters of quasi-circular (MOLA) data. Altimeter Laser

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Figure 15. Mars Global Surveyor (MGS) Mars Orbiter Laser Altimeter (MOLA) data and Mars Express (MEX) Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) data for the north polar cap of Mars. The top image is a radargram from MARSIS, showing data from the surface and subsurface of Mars in the layered deposits that surround the north pole. The MARSIS trace splits into two traces in the center-right of the image, at the point where the ground track crosses from the smooth plains onto the elevated layered deposits on the right. The upper trace is the echo from the surface of the deposits, while the lower trace is interpreted to be the boundary between the lower surface of the deposits and the underlying material. The strength of the lower echo suggests that the intervening material is nearly pure water ice. The time delay between the two echoes reaches a maximum of 21 µs at the right of the image, corresponding to a thickness of ~1.8 km of ice. The bottom image shows the position of the ground track on a topographic map of the area based on MOLA data. The total elevation difference shown in the topographic map is ~2 km between the lowest surface (purple) and the highest (orange). Both of the images are 458 km wide. Image Credit: ASI/NASA/ESA/JPL/Univ. of Rome/MOLA.

GRAVITY AND MAGNETIC DATA Martian atmosphere and the seasonal changes data set that can be used to enhance our under- in the location of carbon dioxide deposited at standing of the Martian gravitational fi eld. For In addition to the novel radar sounding tech- the surface (e.g., Smith et al., 1999c). Similarly, example, the gravity data from MRO will be niques described above, more traditional geo- magnetic data for Mars are used to constrain the used to understand the subsurface structure of physical approaches can also provide data that nature and evolution of the Martian crust (e.g., Mars on the scale of several hundred kilome- constrain the nature and structure of the Martian Acuna et al., 1999) and models of the internal ters, and the rigidity of the planet as a whole. subsurface (e.g., Figures 16 and 17). Models structure and thermal evolution of Mars (e.g., In contrast, MEX can provide gravity data at of the Martian gravitational fi eld are used to Connerney et al., 1999). relatively small wavelengths because of the constrain the nature and evolution of the Mar- Each new mission to Mars provides addi- relatively low periapsis of the spacecraft orbit, tian crust (e.g., Smith et al., 1999b; Neumann tional gravity data: for all orbiting spacecraft, and can therefore provide new constraints on et al., 2004; Wieczorek and Zuber, 2004) and the Doppler shift in the radio communications the local structure of the Martian crust and models of the internal structure and thermal signal can be used to determine the Martian lithosphere. Thus, the gravity data from the evolution of Mars (e.g., Zuber et al., 2000), as gravitational fi eld (e.g., Lemoine et al., 2001). MEX mission have been used to validate exist- well as contributing key data to models of the Each new mission provides a subtly different ing global gravity models developed using data

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Figure 16. Mars global gravity map, based on data from Mars Global Surveyor (MGS) radio tracking, color-coded in mgal. Image credit: NASA/JPL.

obtained at longer wavelengths during earlier geological problems in three dimensions. New spacecraft collected data over a suffi ciently missions (Beuthe et al., 2006). sounding radar instruments on board MEX and long time period (almost a decade) to detect MRO are now helping us to unlock the third recent activity in some Martian gullies (e.g., CONCLUSIONS dimension and develop a better understanding Fig. 18), illustrating the fact that the Martian of the formation and evolution of the Martian surface is still active to some degree (Malin et The combination of data from a variety of surface. The ability to integrate subsurface al., 2006). However, current planetary geologi- planetary science instruments that have been information, such as that provided by MARSIS cal timescales are based on assigning ages to obtained at a range of scales is being used to and SHARAD, is of fundamental importance to planetary surfaces depending on the number help us to address signifi cant geological ques- our understanding of planetary geology. of impact craters identifi ed on that surface. By tions, such as what geological processes oper- Our experiences in combining Mars data unlocking the third dimension, the assump- ate on each planet (and how and when do they from a range of instruments over a range of tions of this dating technique are called into operate)? These extensive data sets address scales will be applied to our studies of other question (e.g., by our new understanding of the fundamental aim of planetary science: to planets. For example, our understanding of the the mechanisms of burial and exhumation of understand the formation and evolution of Saturnian system is rapidly improving through impact craters (e.g., Arvidson et al., 2003), and Earth in a wider context. the combination of different data sets from the the identifi cation of many buried impact craters Imaging instruments at Mars such as those on Cassini-Huygens mission (e.g., Lebreton et al., in the northern hemisphere of Mars (Watters et board MEX and MRO are designed to provide 2005; Stofan et al., 2007; Witasse et al., 2006). al., 2006)). Collecting data over suffi cient time 3-D data sets to complement DEMs provided A major challenge in future planetary stud- periods to quantify the scales, extents, and rates by MOLA, but many of these data sets are still ies is the integration of the fourth dimension: of planetary geological activity (e.g., active limited to the observation of surface outcrops. It time. Over relatively short time periods, this is volcanism on Io and lake level fl uctuations on is necessary to access the subsurface to assess already being achieved. For example, the MGS Titan) is of fundamental importance.

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Figure 17. Mars global magnetic map, based on data from Mars Global Surveyor (MGS) (MAG-ER). Mars does not cur- rently have a global magnetic fi eld. This image shows measurements of the crustal remnant, radial magnetic fi eld, derived from spacecraft tracks below 200 km, color-coded on a global perspective view and overlain on a monochrome shaded relief map of MOLA topography. Image credit: NASA/JPL/GSFC/MAG-ER/MOLA.

Building on the current legacy of planetary REFERENCES CITED Crumpler, L., Des Marais, D.J., de Souza, P.A., Jr., d’Uston, C., Economou, T., Farmer, J., Farrand, W.H., exploration, several further planetary missions are Acuna, M.H., Connerney, J.E.P., Wasilewski, P., Lin, R.P., Folkner, W., Golombek, M., Gorevan, S., Grant, J.A., planned for the future. For more information on Anderson, K.A., Carlson, C.W., McFadden, J., Curtis, Greeley, R., Grotzinger, J., Guinness, E., Hahn, B.C., NASA’s vision for space exploration, see: http:// D.W., Mitchell, D., Reme, H., Mazelle, C., Sauvaud, Haskin, L., Herkenhoff, K.E., Hurowitz, J.A., Hviid, J.A., d’Uston, C., Cros, A., Medale, J.L., Bauer, S.J., S., Johnson, J.R., Klingelhöfer, G., Knoll, A.H., Lan- www.nasa.gov/mission_pages/exploration/main/ Cloutier, P., Mayhew, M., Winterhalter, D., and Ness, dis, G., Leff, C., Lemmon, M., Li, R., Madsen, M.B., index.html. More information on ESA’s program N.F., 1999, Global distribution of crustal magnetisa- Malin, M.C., McLennan, S.M., McSween, H.Y., Ming, “Expanding Frontiers,” and their long-term strat- tion discovered by the Mars Global Surveyor MAG/ER D.W., Moersch, J., Morris, R.V., Parker, T., Rice, J.W., experiment: Science, v. 284, p. 790–793, doi: 10.1126/ Jr., Richter, L., Rieder, R., Rodionov, D.S., Schröder, egy for human exploration of space, called the science.284.5415.790. C., Sims, M. Smith, M., Smith, P., Soderblom, L.A., “Aurora Exploration Programme,” is available at, Albee, A.L., Palluconi, F.D., and Arvidson, R.E., 1998, Sullivan, R., Thompson, S.D., Tosca, N.J., Wang, A., Global Surveyor Mission: Overview and status: Sci- Wänke, H., Ward, J., Wdowiak, T., Wolff, M., Yen, respectively: http://www.esa.int/esaCP/Expand- ence, v. 279, no. 5357, p. 1671–1672, doi: 10.1126/sci- A.., 2006, Overview of the Spirit Mars Explora- ing.html and http://www.esa.int/SPECIALS/ ence.279.5357.1671. tion Rover Mission to Gusev Crater: Landing site to Aurora/index.html. More information on plans Arvidson, R.E., Anderson, R.C., Haldemann, A.F.C., Backstay Rock in the Columbia Hills, Journal of Geo- Landis, G.A., Li, R., Lindemann, R.A., Matijevic, physical Research, v. 111, no. E02S01, DOI:10.1029/ for space exploration from the Japanese Aero- J.R., Morris, R.V., Richter, L., Squyres, S.W., Sul- 2005JE002499. space Exploration Agency (JAXA), the China livan, R.J., and Snider, N.O., 2003, Physical proper- Balme, M. R., Murray, J.B., Ackley, S.F., Muller, J.-P., Kim, ties and localization investigations associated with J.R., 2007, Morphological evidence for a sea-ice origin National Space Administration (CNSA), and the the 2003 Mars Exploration rovers: Journal of Geo- for Elysium Planitia Platy Terrain: Lunar and Planetary Indian Space Research Organization (ISRO), is physical Research, v. 108, no. E12, p. 8070, doi: Science XXXVIII, Abstract no. 2202. available from, respectively: http://www.jaxa.jp/ 10.1029/2002JE002041. Bell, J.F., III, Squyres, S.W., Herkenhoff, K.E., Maki, J.N., Arvidson, R. E., Squyres, S.W., Anderson, R.C., Bell, J.F., Arneson, H.M., Brown, D., Collins, S.A., Dingizian, A., index_e.html, http://www.cnsa.gov.cn/n615709/ III, Blaney, D., Brückner, J., Cabrol, N.A., Calvin, Elliot, S.T., Hagerott, E.C., Hayes, A.G., Johnson, M.J., cindex.html, and http://www.isro.org. W.M., Carr, M.H., Christensen. P.R., Clark, B.C., Johnson, J.R., Joseph, J., Kinch, K., Lemmon, M.T.,

452 Geosphere, December 2007

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/435/854324/i1553-040X-3-6-435.pdf by guest on 01 October 2021 Planetary science ed at 36.6° S, 161.8° W, taken before and taken before W, ed at 36.6° S, 161.8° Figure 18. Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) images of the wall of an unnamed crater in Terra Sirenum, locat Sirenum, Terra in Camera (MOC) images of the wall an unnamed crater (MGS) Mars Orbiter 18. Mars Global Surveyor Figure NASA/JPL/MSSS. Image Credit: gully activity. recent after

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Morris, R.V., Scherr, L., Schwochert, M., Shepard, Edgett, K.S., 2005, The sedimentary rocks of Sinus Meridi- T., Clancy, R.T., Darlington, E.H., Des Marais, D., M.K., Smith, G.H., Sohl-Dickstein, J.N., Sullivan, R.J., ani: Five key observations from data acquired by the Espiritu, R., Fort, D., Green, R., Guinness, E., Hayes, Sullivan, W.T., and Wadsworth, M., 2003, Exploration Mars Global Surveyor and Mars Odyssey orbiters: J., Hash, C., Heffernan, K., Humm, D., Hutcheson, J., Rover Athena Panoramic Camera (Pancam) investiga- Mars, v. 1, p. 5–58, DOI: 10.1555/mars.2005.0002. Izenberg, N., Lees, J., Malaret, E., Martin, T., McGov- tion: Journal of Geophysical Research, v. 108, no. E12, Edgett, K.S., and Malin, M.C., 2002, Martian sedimentary ern, J.A., McGuire, P., Morris, R., Mustard, J., Pelkey, p. 8063, doi: 10.1029/2003JE002070. rock stratigraphy: Outcrops and interbedded craters of S., Robinson, M., Roush, T., Seelos, F., Seelos, K., Bibring, J.-P., Langevin, Y., Gendrin, A., Gondet, B., Poulet, northwest Sinus Meridiani and southwest : Slavney, S., Smith, M., Shyong, W.J., Strohbehn, K., F., Berthé, M., Souffl ot, A., Arvidson, R. E., Mangold, Geophysical Research Letters, v. 29, no. 24, p. 2179, Taylor, H., Wirzburger, M., and Wolff, M., 2006, First N., Mustard, J. F., Drossart, P., and the OMEGA team, doi: 10.1029/2002GL016515. CRISM Observations of Mars [abs.]: Eos (Transac- 2005, Surface diversity as revealed by the OMEGA/ Edgett, K.S., and Parker, T.J., 1997, Water on early Mars: tions, American Geophysical Union), v. 87, p. 52, Mars Express observations: Science, v. 307, no. 5715, Possible subaqueous sedimentary deposits covering Abstract no. P33A–04. p. 1576–1581, doi: 10.1126/science.1108806. ancient cratered terrain in western Arabia and Sinus Murchie, S.L., Arvidson, R., Bedini, P., Beisser, K., Bibring, J.-P., Langevin, Y., Mustard, J. F., Poulet, F., Arvid- Meridiani: Geophysical Research Letters, v. 24, no. 22, Bibring, J.P., Bishop, J.., Boldt, J., Cavender, P., Choo, son, R. E., Gendrin, A., Gondet, B., Mangold, N., Pinet, p. 2897–2900, doi: 10.1029/97GL02840. T., Clancy, R.T., Darlington, E.H., Des Marais, D., P., Forget, F., and the OMEGA team, 2006, Global Evans, L.G., Reedy, R.C., Starr, R.D., Kerry, K.E. and Espiritu, R., Fort, D., Green, R., Guinness, E., Hayes, mineralogical and aqueous Mars history derived from Boynton, W.V., 2006, Analysis of gamma ray spectra J., Hash, C., Heffernan, K., Hemmler, J., Heyler, OMEGA/Mars Express data: Science, v. 312, no. 5772, measured by Mars Odyssey: Journal of Geophysi- G., Humm, D., Hutcheson, J., Izenberg, N., Lee, R., p. 400–404, doi: 10.1126/science.1122659. cal Research, v. 111, no. E03S04, DOI:10.1029/ Lees, J., Lohr, D., Malaret, E., Martin, T., McGovern, Beuthe, M., Rosenblatt, P., Dehant, V., Barriot, J.-P., Pät- 2005JE002657. J.A., McGuire, P., Morris, R., Mustard, J., Pelkey, zold, M., Häusler, B., Karatekin, O., Le Maistre, S., Frey, H.V., Roark, J.H., Shockey, K.M., Frey, E.L., Saki- S., Rhodes, E., Robinson, M., Roush, T., Schaefer, and Van Hoolst, T., 2006, Assessment of the Martian moto, S.E.H., 2002, Ancient lowlands on Mars: E., Seagrave, G., Seelos, F., Silverglate, P., Slavney, gravity fi eld at short wavelength with Mars Express: Geophysical Research Letters, v. 29, no. 10, doi: S., Smith, M., Shyong, W.J.., Strohbehn, K., Taylor, Geophysical Research Letters, v. 33, no. L03203, doi: 10.1029/2001GL013832. H., Thompson, P., Tossman, B., Wirzburger, M., and 10.1029/2005GL024317. Gesch, D.B., Muller, J.-P., and Farr, T.G., 2006, The Shuttle Wolff, M., 2007, Compact Reconnaissance Imaging Boynton, W.V., Feldman, W.C., Mitrofanov, I.G., Radar Topography Mission—Data Validation and Spectrometer for Mars (CRISM) on Mars Recon- Evans, L.G., Reedy, R.C., Squyres, S.W., Starr, Applications: Photogrammetric Engineering and naissance Orbiter (MRO): Journal of Geophysical R., Trombka, J.I., d’ston, C., Arnold, J.R., Englert, Remote Sensing, v. 72, no. 3, p. 233. Research, v. 112, no. E5, doi: 10.1029/2006JE002682 P.A.J., Metzger, A.E., Wänke, H., Brückner, J., Head, J.W., III, Kreslavsky, M.A., and Pratt, S., 2002, North- (in press). Drake, D.M., Shinohara, C., Fellows, C., Hamara, ern lowlands of Mars - Evidence for widespread volca- Murray, J.B., Muller, J.-P., Neukum, G., Werner, S.C., van D.K., Harshman, K., Kerry, K., Turner, C., Ward, nic fl ooding and tectonic deformation in the Gasselt, S., Hauber, E., Markiewicz, W.J., Head, J.W., M. Barthe, H., Fuller, K.R., Storms, S.A., Thornton, Period: Journal of Geophysical Research, v. 107, III, Foing, B.H., Paige, D., Mitchell, K.L., Portyankina, G.W., Longmire, J.L., Litvak, M.L., and Ton’chev, no. E1, doi: 10.1029/2000JE001445. G., and the HRSC Co-investigator Team, 2005, Evi- A.K., 2004, The Mars Odyssey Gamma-Ray Spec- Herkenhoff, K.E., Squyres, S.W., Arvidson, R.E., Bass, D.S., dence from the Mars Express High Resolution Stereo trometer Instrument Suite: Space Science Reviews, Bell, J.F., III, Bertelsen, P., Ehlmann, B.L., Farrand, W., Camera for a frozen sea close to Mars’ equator: Nature, v. 110, no. 1–2, p. 37–83, doi: 10.1023/B:SPAC.00 Gaddis, L., Greeley, R., Grotzinger, J., Hayes, A.G., v. 434, p. 352, doi: 10.1038/nature03379. 00021007.76126.15. Hviid, S.F., Johnson, J.R., Jolliff, B., Kinch, K.M., Neukum, G., Jaumann, R., Hoffmann, H., Hauber, E., Head, Christensen, P.R., and Ruff, S.W., 2004, Formation of the Knoll, A.H., Madsen, M.B., Maki, J.N., McLennan, J. W., III, Basilevsky, A.T., Ivanov, B.A., Werner, S.C., hematite-bearing unit in Meridiani Planum: Evi- S.M., McSween, H.Y., Jr., Ming, D.W., Rice, J.W., Jr., van Gasselt, S., Murray, J.B., McCord, T., and the dence for deposition in standing water: Journal of Richter, L., Sims, M., Smith, P.H., Soderblom, L.A., HRSC Co-Investigator Team, 2004, Recent and epi- Geophysical Research, v. 109, no. E08003, doi: Spanovich, N., Sullivan, R., Thompson, S., Wdow- sodic volcanic and glacial activity on Mars revealed 10.1029/2003JE002233. iak, T., Weitz, C., and Whelley, P., 2004, Evidence by the High Resolution Stereo Camera: Nature, v. 432, Christensen, P.R., Banfi eld, J.L., Clark, R.N., Edgett, K.S., from Opportunity’s microscopic imager for water on no. 7020, p. 971–979, doi: 10.1038/nature03231. Hamilton, V.E., Hoefen, T., Kieffer, H.H., Kuzmin, Meridiani Planum: Science, v. 306, p. 1727–1730, doi: Neumann, G. A., Zuber, M.T., Wieczorek, M.A., McGov- R.O., Lane, M.D., Malin, M.C., Morris, R.V., Pearl, 10.1126/science.1105286. ern, P.J., Lemoine, F.G., and Smith, D.E., 2004, The J.C., Pearson, R., Roush, T.L., Ruff, S.W., and Smith, Hynek, B.M., 2004, Implications for hydrologic processes crustal structure of Mars from gravity and topogra- M.D., 2000, Detection of crystalline hematite mineral- on Mars from extensive bedrock outcrops through- phy: Journal of Geophysical Research, v. 109, doi: ization on Mars by the Thermal Emission Spectrom- out Terra Meridiani: Nature, v. 431, p. 156–159, doi: 10/1029/2004JE002262. eter: Evidence for near-surface water: Journal of Geo- 10.1038/nature02902. Newsom, H.E., Barber, C.A., Hare, T.M., Schelble, R.T., physical Research, v. 105, no. E4, p. 9623–9642, doi: Hynek, B.M., Arvidson, R.E., and Phillips, R.J., 2002, Geo- Sutherland, V.A., and Feldman, W.C., 2003, Paleo- 10.1029/1999JE001093. logic setting and origin of Terra Meridiani hematite lakes and impact basins in southern Arabia Terra, Christensen, P.R., Morris, R.V., Lane, M.D., Banfi eld, J.E., deposit on Mars: Journal of Geophysical Research, including Meridiani Planum: Implications for the and Malin, M.C., 2001, Global mapping of Martian v. 107, no. E10, p. 5088, doi: 10.1029/2002JE001891. formation of hematite deposits on Mars: Journal of hematite mineral deposits: Remnants of water-driven Jaeger, W.L., Keszthelyi, L.P., McEwen, A.S., Russell, P.S. and Geophysical Research, v. 108, no. E12, p. 8075, doi: processes on early Mars: Journal of Geophysical the HiRISE Team, 2007, Early HiRISE observations of 10.1029/2002JE001993. Research, v. 106, no. E10, p. 23,873–23,885, doi: : A lava-draped channel system: Lunar Newsom, H.E., Crumpler, L.S., Reedy, R.C., Petersen, 10.1029/2000JE001415. and Planetary Science XXXVIII, Abstract no. 2066. M.T., Gary Newsom, G.C., Evans, L.G., Taylor, G.J., Christensen, P.R., Wyatt, M.B., Glotch, T.D., Rogers, A.D., Lebreton, J.-P., Witasse, O., Sollazzo, C., Blancquaert, T., Keller, J.M., Janes, D.M., Boynton, Kerry, K.E., and Anwar, S., Arvidson, R.E., Bandfi eld, J.L., Blaney, Couzin, P., Schipper, A.-M., Jones, J.B., Matson, D.L., Karunatillake, Suniti 2007, Geochemistry of Martian D.L., Budney, C., Calvin, W.M., Fallacaro, A., Fer- Gurvits, L.I., Atkinson, D.H., Kazeminejad, B., and soil and bedrock in mantled and less mantled terrains gason, R.L., Gorelick, N., Graff, T.G., Hamilton, V.E., Pérez-Ayúcar, M., 2005, An overview of the descent with gamma ray data from Mars Odyssey: Journal of Hayes, A.G., Johnson, J.R., Knudson, A.T., McSween, and landing of the Huygens probe on Titan: Nature, Geophysical Research, v. 112, no. E03, p. S12, doi: H.Y., Jr., Mehall, G.L., Mehall, L.K., Moersch, J.E., v. 438, p. 758–764, doi: 10.1038/nature04347. 10.1029/2006JE002680. Morris, R.V., Smith, M.D., Squyres, S.W., Ruff, S.W., Lemoine, F.G., Smith, D.E., Rowlands, D.D., Zuber, M.T., Okubo, C.H., and McEwen, A.S., 2007, Fracture-controlled and Wolff, M.J., 2004, Mineralogy at Meridiani Pla- Neumann, G.A., Chinn, D.S., and Pavlis, D.E., 2001, paleo-fl uid fl ow in Candor , Mars, Science, num from the Mini-TES Experiment on the Opportu- An improved solution of the gravity fi eld of Mars v. 315, no. 5814, p. 983–985, DOI: 10.1126/sci- nity Rover: Science, v. 306, no. 5702, p. 1733–1739, (GMM-2B) from Mars Global Surveyor: Journal of ence.1136855. doi: 10.1126/science.1104909. Geophysical Research, v. 106, p. 23,359–23,376, doi: Ormo, J., Komatsu, G., Chan, M.A., Beitler, B., and Parry, Christensen, P.R., Ruff, S.W., Fergason, R.L., Glotch, T.D., 10.1029/2000JE001426. W.T., 2004, Geological features indicative of processes Gorelick, N., Jakosky, B.M., Lane, M.D., McEwen, McEwen, A.S., Eliason, E.M., Bergstrom, J.W., Bridges, related to the hematite formation in Meridiani Planum A.S., McSween, H.Y., Jr., Mehall, G.L., Milam, K., N.T., Hansen, C.J., Delamere, W.A., Grant, J.A., and Aram Chaos, Mars: A comparison with diagenetic Moersch, J.E., Pelkey, S.M., Rogers, A.D., and Wyatt, Gulick, V.C., Herkenhoff, K.E., Keszthelyi, L., Kirk, hematite deposits in southern Utah, USA: Icarus, v. 171, W.B., 2005, Mars Exploration Rover candidate landing R.L., Mellon, M.T., Squyres, S.W., Thomas, N., and no. 2, p. 295–316, doi: 10.1016/j.icarus.2004.06.001. sites as viewed by THEMIS: Icarus, v. 176, p. 12–43, Weitz, C.M., 2007, Mars Reconnaissance Orbit- Pelkey, S.M., Mustard, J.F., Murchie, S., Clancy, R.T., doi: 10.1016/j.icarus.2005.01.004. er’s High Resolution Imaging Science Experiment Wolff, M., Smith, M., Milliken, R., Bibring, J.-P., Gen- Connerney, J.E.P., Acuna, M.H., Wasilewski, P., Ness, N.F., (HiRISE): Journal of Geophysical Research, doi: drin, A., Poulet, F., Langevin, Y., and Gondet, B., 2007, Reme, H., Mazelle, C., Vignes, D., Lin, R.P., Mitchell, 10.1029/2005JE002605. CRISM multispectral summary products: Param- D., and Cloutier, P., 1999, Magnetic lineations in the Malin, M.C., Edgett, K.S., Posiolova, L.V., McColley, S.M., eterizing mineral diversity on Mars from refl ectance: ancient crust of Mars: Science, v. 284, p. 794–798, doi: and Noe Dobrea, E.Z., 2006, Present-day impact cra- Journal of Geophysical Research, v. 112, no. E8, doi: 10.1126/science.284.5415.794. tering rate and contemporary gully activity on Mars: 10.1029/2006JE002831. Crown, D. A.; Berman, D. C.; Bleamaster, L. F., 2007, Science, v. 314, no. 5805, p. 1573, doi: 10.1126/sci- Picardi, G., Plaut, J.J., Biccari, D., Bombaci, O., Cala- Contemporary Gully Activity on Mars: Insights from ence.1135156. brese, D., Cartacci, M., Cicchetti, A., Clifford, S.M., Regional Geology, Lunar and Planetary Science XXX- Murchie, S., Arvidson, R., Bedini, P., Beisser, K., Bibring, Edenhofer, P., Farrell, W.M., Federico, C., Frigeri, A., VIII, Abstract no. 1726. J., Bishop, J., Brown, A., Boldt, J., Cavender, P., Choo, Gurnett, D.A., Hagfors, T., Heggy, E., Herique, A.,

454 Geosphere, December 2007

Downloaded from http://pubs.geoscienceworld.org/gsa/geosphere/article-pdf/3/6/435/854324/i1553-040X-3-6-435.pdf by guest on 01 October 2021 Planetary science

Huff, R.L., Ivanov, A.B., Johnson, W.T.K., Jordan, Squyres, S.W., Arvidson, R.E., Bell, J.F., III, Brückner, J., Drake, D., 2006, Bulk composition and early differ- R.L., Kirchner, D.L., Kofman, W., Leuschen, C.J., Cabrol, N.A., Calvin, W., Carr, M.H., Christensen, P.R., entiation of Mars: Journal of Geophysical Research, Nielsen, E., Orosei, R., Pettinelli, E., Phillips, R.J., Clark, B.C., Crumpler, L., Des Marais, D.J., d’Uston, v. 111, no. E03, p. S10, doi: 10.1029/2005JE002645. Plettemeier, D., Safaeinili, A., Seu, R., Stofan, E.R., C., Economou, T., Farmer, J., Farrand, W., Folkner, W., Watters, T.R., Leuschen, C.J., Plaut, J.J., Picardi, G., Safa- Vannaroni, G., Watters, T.R., and Zampolini, E., 2005, Golombek, M., Gorevan, S., Grant, J.A., Greeley, R., einili, A., Clifford, S.M., Farrell, W.M., Ivanov, A.B., Radar soundings of the subsurface of Mars: Science, Grotzinger, J., Haskin, L., Herkenhoff, K.E., Hviid, Phillips, R.J., and Stofan, E.R., 2006, MARSIS radar v. 310, no. 5756, p. 1925–1928, doi: 10.1126/sci- S., Johnson, J., Klingelhöfer, G., Knoll, A., Landis, sounder evidence of buried basins in the northern low- ence.1122165. G., Lemmon, M., Li, R., Madsen, M.B., Malin, M.C., lands of Mars: Nature, v. 444, no. 7121, p. 905–908, Phillips, R.J., Seu, R., Biccari, D., Campbell, B.A., Plaut, McLennan, S.M., McSween, H.Y., Jr., Ming, D.W., doi: 10.1038/nature05356. J.J., Zuber, M.T., Murchie, S., Byrne, S., Safaeinili, Moersch, J., Morris, R.V., Parker, T., Rice, J. W., Jr., Wieczorek, M.A., and Zuber, M.T., 2004, Thickness of the A., Orosei, R., Marinangeli, L., Masdea, A., Picardi, Richter, L., Rieder, R., Sims, M., Smith, M., Smith, P., Martian crust: Improved constraints from geoid-to- G., Smrekar, S.E., Carter, L.M., Putzig, N.E., Nunes, Soderblom, L.A., Sullivan, R., Wänke, H., Wdowiak, topography ratios: Journal of Geophysical Research, D.C., and the Sharad Team, 2007, North Polar Deposits T., Wolff, M., and Yen, A., 2004a, The Spirit Rover’s v. 109, no. E01009, doi: 10.1029/2003JE002153. on Mars: New Insights from MARSIS, SHARAD and Athena Science Investigation at Gusev Crater, Mars: Witasse, O., Lebreton, J.-P., Bird, M.K., Dutta-Roy, R., Other MRO Instruments: Lunar and Planetary Science Science, v. 305, no. 5685, p. 794–799, DOI: 10.1126/ Folkner, W.M., Preston, R.A., Asmar, S.W., Gurvits, XXXVIII, Abstract no. 1925. science.3050794. L.I., Pogrebenko, S.V., Avruch, I.M., Campbell, R.M., Seu, R., Biccari, D., Orosei, R., Lorenzoni, L.V., Phillips, Squyres, S.W., Arvidson, R.E., Bell, J.F., III, Brückner, J., Bignall, H.E., Garrett, M.A., van Langevelde, H.J., R.J., Marinangeli, L., Picardi, G., Masdea, A., and Cabrol, N.A., Calvin, W., Carr, M.H., Christensen, P.R., Parsley, S.M., Reynolds, C., Szomoru, A., Reynolds, Zampolini, E., 2004, SHARAD: The MRO 2005 shal- Clark, B.C., Crumpler, L., Des Marais, D.J., d’Uston, J.E., Phillips, C.J., Sault, R.J., Tzioumis, A.K., Ghigo, low radar: Planetary and Space Science, v. 52, p. 157– C., Economou, T., Farmer, J., Farrand, W., Folkner, W., F., Langston, G., Brisken, W., Romney, J.D., Mujunen, 166, doi: 10.1016/j.pss.2003.08.024. Golombek, M., Gorevan, S., Grant, J.A., Greeley, R., A., Ritakari, J., Tingay, S.J., Dodson, R.G., van’t Seu, R., Phillips, R.J., Biccari, D., Orosei, R., Masdea, A., Grotzinger, J., Haskin, L., Herkenhoff, K.E., Hviid, Klooster, C.G.M., Blancquaert, T., Coustenis, A., Gen- Picardi, G., Safaeinili, A., Campbell, B.A., Plaut, J.J., S., Johnson, J., Klingelhöfer, G., Knoll, A., Landis, dron, E., Sicardy, B., Hirtzig, M., Luz, D., Negrao, A., Marinangeli, L., Smrekar, S.E., and Nunes, D.C., 2007, G., Lemmon, M., Li, R., Madsen, M.B., Malin, M.C., Kostiuk, T., Livengood, T.A., Hartung, M., de Pater, SHARAD sounding radar on the Mars Reconnaissance McLennan, S.M., McSween, H.Y., Jr., Ming, D.W., I., Ádámkovics, M., Lorenz, R.D., Roe, H., Schaller, Orbiter: Journal of Geophysical Research, v. 112, Moersch, J., Morris, R.V., Parker, T., Rice, J.W., Jr., E., Brown, M., Bouchez, A.H., Trujillo, C.A., Buratti, no. E5, doi: 10.1029/2006JE002745 Richter, L., Rieder, R., Sims, M., Smith, M., Smith, P., B.J., Caillault, L., Magin, T., Bourdon, A., and Laux, Smith, D.E., Zuber, M.T., Solomon, S.C., Phillips, R.J., Soderblom, L.A., Sullivan, R., Wänke, H., Wdowiak, C., 2006, Overview of the coordinated ground-based Head, J.W., III, Garvin, J.B., Banerdt, W.B., Muhleman, T., Wolff, M., and Yen, A., 2004b, The Opportunity observations of Titan during the Huygens mission: D.O., Pettengill, G.H., Neumann, G.A., Lemoine, F.G., Rover’s Athena Science Investigation at Meridiani Pla- Journal of Geophysical Research, v. 111, no. E07S01, Abshire, J.B., Aharonson, O., Brown, C.D., Hauck, num, Mars: Science, v. 306, no. 5702, p. 1698–1703, doi: 10.1029/2005JE002640. S.A., Ivanov, A.B., McGovern, P.J., Zwally, H.J., and doi: 10.1126/science.1106171. Zuber, M.T., Smith, D.E., Solomon, S.C., Abshire, J.B., Duxbury, T.C., 1999a, The Global topography of Mars Squyres, S.W., Arvidson, R.E., Bollen, D., Bell, J.F., III, Afzal, R.S., Aharonson, O., Fishbaugh, K., Ford, P.G., and implications for surface evolution: Science, v. 284, Brückner, J., Cabrol, N.A., Calvin, W.M., Carr, M.H., Frey, H.V., Garvin, J.B., Head, J.W., III, Ivanov, A.B., p. 1495–1503, doi: 10.1126/science.284.5419.1495. Christensen, P.R., Clark, B.C., Crumpler, L., Des Johnson, C.L., Muhleman, D.O., Neumann, G.A., Smith, D.E., Sjogren, W.L., Tyler, G.L., Balmino, G., Lem- Marais, D.J., d’Uston, C., Economou, T., Farmer, J., Pettengill, G.H., Phillips, R.J., Sun, X., Zwally, H.J., oine, F.G., and Konopliv, A.S., 1999b, The gravity fi eld Farrand, W.H., Folkner, W., Gellert, R., Glotch, T.D., Banerdt, W.B., and Duxbury, T.C., 1998, Observations of Mars: Results from Mars Global Surveyor: Science, Golombek, M., Gorevan, S., Grant, J.A., Greeley, R., of the north polar region of Mars from the Mars Orbiter v. 286, p. 94–97, doi: 10.1126/science.286.5437.94. Grotzinger, J., Herkenhoff, K.E., Hviid, S., Johnson, Laser Altimeter: Science, v. 282, no. 5396, p. 2053– Smith, D.E., Zuber, M.T., Haberle, R.M., Rowlands, D.D., J.R., Klingelhöfer, G., Knoll, A.H., Landis, G., Lem- 2060, doi: 10.1126/science.282.5396.2053.

and Murphy, J.R., 1999c, The Mars seasonal CO2 mon, M., Li, R., Madsen, M.B., Malin, M.C., McLen- Zuber, M.T., Solomon, S.C., Phillips, R.J., Smith, D.E., cycle and the time variation of the gravity fi eld: A nan, S.M., McSween, M.Y., Ming, D.W., Moersch, J., Tyler, G.L., Aharonson, O., Balmino, G., Banerdt, general circulation model simulation: Journal of Geo- Morris, R.V., Parker, T., Rice, J.W., Jr., Richter, L., Rie- W.B., Head, J.W., III, Johnson, C.L., Lemoine, F.G., physical Research, v. 104, no. E1, p. 1885–1896, doi: der, R., Schröder, C., Sims, M., Smith, M., Smith, P., McGovern, P.J., Neumann, G.A., Rowlands, D.D., and 10.1029/1998JE900024. Soderblom, L.A., Sullivan, R., Tosca, N.J., Wänke, H., Zhong, S., 2000, Internal structure and early thermal Smith, D.E., Zuber, M.T., Frey, H.V., Garvin, J.B., Head, Wdowiak, T., Wolff, M., and Yen, A., 2006, Overview evolution of Mars from Mars Global Surveyor topog- J.W., III, Muhleman, D.O., Pettengill, G.H., Phillips, of the Opportunity Mars Exploration Rover Mission to raphy and gravity data: Science, v. 287, p. 1788–1793, R.J., Solomon, S.C., Zwally, H.J., Banerdt, W.B., Dux- Meridiani Planum: Eagle Crater to Purgatory Ripple: doi: 10.1126/science.287.5459.1788. bury, T.C., Golombek, M.P., Lemoine, F.G., Neumann, Journal of Geophysical Research, v. 111, no. E12, Zurek, R.W., and Smrekar, S.E., 2007, An overview of the G.A., Rowlands, D.D., Aharonson, O., Ford, P.G., Iva- p. S12, doi: 10.1029/2006JE002771. Mars Reconnaissance Orbiter (MRO) science mission: nov, A.B., Johnson, C.L., McGovern, P.J., Abshire, J.B., Stofan, E.R., Elachi, C., Lunine, J.I., Lorenz, R.D., Stiles, Journal of Geophysical Research, v. 112, no. E05S01, Afzal, R.S., and Sun, X., 2001, Orbiter Laser Altimeter: B., Mitchell, K.L., Ostro, S., Soderblom, L.A., Wood, DOI:10.1029/2006JE002701. Experiment summary after the fi rst year of global map- C., Zebker, H., Wall, S., Janssen, M., Kirk, R., Lopes, ping of Mars: Journal of Geophysical Research, v. 106, R., Paganelli, F., Radebaugh, J., Wye, L., Anderson, Y., p. 23,689–23,722, doi: 10.1029/2000JE001364. Allison, M., Boehmer, R., Callahan, P., Encrenaz, P., Snyder, C.W., and Moroz, V.I., 1992, Spacecraft Explora- Flamini, E., Francescetti, G., Gim, Y., Hamilton, G., tion, in Kieffer, H.H., Jakosky, B.M., and Matthews, Hensley, S., Johnson, W.T.K., Kelleher, K., Muhle- M.S., eds., Mars: University of Arizona Press [Tuc- man, D., Paillou, P., Picardi, G., Posa, F., Roth, L., Seu, son], p. 969–1016. R., Shaffer, S., Vetrella, S., and West, R., 2007, The Sprague, A.L., Boynton, W.V., Kerry, K.E., Janes, D.M., lakes of Titan: Nature, v. 445, p. 61–64, doi: 10.1038/ Kelly, N.J., Crombie, M.K., Nelli, S.M., Murphy, nature05438. J.R., Reedy, R.C., and Metzger, A.E., 2007, Mars’ Taylor, G.J., Boynton, W., Brückner, J., Wänke, H., Dreibus, atmospheric argon: Tracer for understanding Martian G., Kerry, K., Keller, J., Reedy, R., Evans, L., Starr, atmospheric circulation and dynamics: Journal of Geo- R., Squyres, S., Karunatillake, S., Gasnault, O., Mau- MANUSCRIPT RECEIVED 5 FEBRUARY 2007 physical Research, v. 112, no. E03S02, DOI:10.1029/ rice, S., d’Uston, C., Englert, P., Dohm, J., Baker, REVISED MANUSCRIPT RECEIVED 18 MAY 2007 2005JE002597. V., Hamara, D., Janes, D., Sprague, A., Kim, K., and MANUSCRIPT ACCEPTED 31 MAY 2007

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