Publications

The sub-kilometer scale vertical of the martian surface in the polar regions can be investigated using calibrated, optical pulse width data provided by the Mars Orbiter Laser Altimeter (MOLA). Garvin and others have previously discussed initial observations of what we have called total vertical roughness or TVR, as derived from MOLA optical pulse width observations acquired during the pre-mapping phases of the Mars Global Surveyor (MGS) mission. Here we present the first assessment of the Mars polar region properties of the TVR parameter from more than nine months of continuous mapping by MOLA as part of the MGS mapping mission. Other than meter-scale surface properties directly inferred from Mars Orbiter Camera (MOC) images, MOLA measurements of footprint-scale TVR represent the only direct measurements of the local vertical structure of the martian surface at approx. 150 m length scales. These types of data have previously been shown to correlate with geologic process histories for terrestrial desert surfaces on the basis of Shuttle Laser Altimeter (SLA) observations. Additional information is obtained in the original extended abstract.

The concept of a frontier is a commonplace metaphor in the physical sciences, as well as in the history of exploration. Today, one of the most tangible and alluring of all such frontiers is represented by the surface of Mars. This is because of the literally phenomenal scientific progress that has resulted from the intensified robotic exploration of the Red Planet since 1996. In little more than a decade (1996–2007), scientific viewpoints have been altered more profoundly than in the previous 30 + years. Some would describe this radical alteration in thinking as a scientific revolution. A case for this perspective is made in a convincing fashion here in The Martian Surface: Composition, Mineralogy, and Physical Properties, edited by Jim Bell and written by him and 82 other colleagues who study Mars for a living. Indeed, since the dawn of the Space Age, now in its 50th year (1957–2007), thoughts have often drifted to the so-called “Martian frontier,” with an ever-changing and sometimes disappointing scientific appreciation of what it might offer. This book puts the emerging “new Mars” into a modern scientific context on the basis of an ensemble of up-to-date scientific hypotheses and viewpoints. It brings Mars alive and promotes prospects for future scientific exploration that are certain to continue the revolution at hand.

Characteristics of rock populations on the surfaces of Mars and Venus can be derived from analyses of rock morphology and morphometry data. We present measurements of rock sizes and sphericifies made from Viking lander images using an interactive digital image display system. The rocks considered are in the gravel size range (16-256 mm in diameter). Mean sphericities, form ratios, and roundness factors are found to be very similar for both Viking lander sites. Size distributions, however, demonstrate differences between the sites; there are significantly more cobble size fragments at VL-2 than at VL-1. A model calling for aphanitic basalts emplaced as ejecta or lava flows at the Viking sites is supported by the rock shape, size, and roundness data. Morphologic features pertaining to the modification history of a rock are considered for Mars and Venus. A multi-parameter clustering algorithm is utilized to objectively categorize martian and venusian rocks in terms of various criteria. Erosional markings such as flutes are demonstrated to be most important in separating VL-1 rock morphologic groups, while rock form (i.e., shape) represents the primary separator of subpopulations at VL-2 and the Venera landing sites. Fillets are common around VL-1 and Venera 10 fragments. Obstacle scours occur frequently only at VL-1. Cavities in rocks are ubiquitous at all lander sites except Venera 9. Eolian processes, possibly assisted by local solution weathering, are a strong candidate for the origin of cavities and flutes in martian rocks. Rock populations on Earth typically contain morphological information p ertinent to their compositions, modes of origin, emplacement styles, and subsequent weathering histories (Ollier, 1969; Folk, 1974). Terrestrial analogues for the Martian environment (Morris etal., 1972, McCauley etal., 1979), permit some inferences to be made about the evolution of the Martian surface. Previous studies of block fields and fine particles on Mars (Moore etal., 1977, Evans and Adams, 1979; Strickland, 1979), and Venus (Florensky et al., 1977; Keldysh, 1979), have identified rock subpopulations within the fields of view of the Viking and Venera landers, but have lacked the large-scale data base required for multiple-parameter morphological analysis. In this report, we provide an overview of a data collection and analysis scheme that has been developed for the interpretation of rock morphology from lander images (Garvin et al., 1980). Emphasis is placed here on our approach to solving the problem of how to best characterize rock populations on planetary surfaces. It involves the collection of quantitative data such as rock size and sphericity, as well as qualitative information regarding morphological features. Full descriptions of the morphological attributes chosen with specific rock examples are presented. Data analysis techniques are also

Quantitative sedimentologic analysis of gravel surfaces dominated by pebble-sized clasts has been employed in an effort to untangle aspects of the provenance of surface sediments on Mars using Curiosity's MARDI nadir-viewing camera operated at twilight Images have been systematically acquired since sol 310 providing a representative sample of gravel-covered surfaces since the rover departed the Shaler region. The MARDI Twilight imaging dataset offers approximately 1 millimeter spatial resolution (slightly out of focus) for patches beneath the rover that cover just under 1 m2 in area, under illumination that makes clast size and inter-clast spacing analysis relatively straightforward using semi- automated codes developed for use with nadir images. Twilight images are utilized for these analyses in order to reduce light scattering off dust deposited on the front MARDI lens element during the terminal stages of Curiosity's entry, descent and landing. Such scattering is worse when imaging bright, directly-illuminated surfaces; twilight imaging times yield diffusely-illuminated surfaces that improve the clarity of the resulting MARDI product. Twilight images are obtained between 10-30 minutes after local sunset, governed by the timing of the end of the no-heat window for the camera. Techniques were also utilized to examine data terrestrial locations (the Kau Desert in Hawaii and near Askja Caldera in Iceland). Methods employed include log hyperbolic size distribution (LHD) analysis and Delauney Triangulation (DT) inter-clast spacing analysis. This work extends the initial results reported in Yingst et al., that covered the initial landing zone, to the Rapid-Transit Route (RTR) towards Mount Sharp.

On the basis of observed shapes and volumetric estimates, we interpret small, dome‐like features on radar images of Venus to be analogs of Icelandic lava‐shield volcanoes. Using morphometric data for venusian domes in Aubele and Slyuta (in press), as well as our own measurements of representative dome volumes and areas from Tethus Regio, we demonstrate that the characteristic aspect ratios and flank slopes of these features are consistent with a subclass of low Icelandic lava‐shield volcanoes (LILS ). LILS are slightly convex in cross‐section with typical flank slopes of ∼3°. Plausible lava‐shield‐production rates for the venusian plains suggest formation of ∼53 million shields over the past 0.25 Ga. The cumulative global volume of lava that would be associated with this predicted number of lava shields is only a factor of 3–4 times that of a single oceanic composite shield volcano such as Mauna Loa. The global volume of all venusian lava shields in the 0.5–20‐km size range would only contribute a meter of resurfacing over geologically significant time scales. Thus, venusian analogs to LILS may represent the most abundant landform on the globally dominant plains of Venus, but would be insignificant with regard to the global volume of lava extruded. As in Iceland, associated lavas from fissure eruptions probably dominate plains volcanism and should be evident on the higher resolution Magellan radar images.

NASA is embarking on a grand journey of exploration that naturally integrates the past successes of the Apollo missions to the Moon, as well as robotic science missions to Mars, to Planet Earth, and to the broader Universe. The US Vision for Space Exporation (VSE) boldly lays out a plan for human and robotic reconnaissance of the accessible Universe, starting with the surface of the Moon, and later embracing the surface of Mars. Sustained human and robotic access to the Moon and Mars will enable a new era of scientific investigation of our planetary neighbors, tied to driving scientific questions that pertain to the evolution and destiny of our home planet, but which also can be related to the search habitable worlds across the nearby Universe. The Apollo missions provide a vital legacy for what can be learned from the Moon, and NASA is now poised to recapture the lunar frontier starting with the flight of the Lunar Reconnaissance Orbiter (LRO) in late 2008. LRO will provide a new scientific context from which joint human and robotic exploration will ensue, guided by objectives some of which are focused on the grandest scientific challenges imaginable : Where did we come from? Are we alone? and Where are we going? The Moon will serve as an essential stepping stone for sustained human access and exploration of deep space and as a training ground while robotic missions with ever increasing complexity probe the wonders of Mars. As we speak, an armada of spacecraft are actively investigating the red planet both from orbit (NASA's Mars Reconnaissance Orbiter and Mars Odyssey Orbiter, plus ESA's Mars Express) and from the surface (NASA's twin Mars Exploration Rovers, and in 2008 NASA's Phoenix polar lander). The dramatically changing views of Mars as a potentially habitable world, with its own flavor of global climate change and unique climate records, provides a new vantage point from which to observe and question the workings of our own planet Earth. By 2010 NASA will have its first mobile analytical laboratory operating on the surface of Mars (Mars Science Laboratory) in search of potentially subtle expressions of past life or at least of life-hospitable environments. Meanwhile back here on Planet Earth, NASA will be continuing to implement an increasingly comprehensive program of robotic missions that address major issues associated with global climate variability, and the variables that affect the quality of human life on our home planet. Ultimately, the fmits of NASA's emergent program of Exploration (VSE) will provide never-beforepossible opportunities for scientific leadership and advancement, culminating in a new state of awareness from which to better plan for the sustainability of life on Earth and for extending Earth life to the Moon and eventually to Mars. As NASA nears its 50th anniversary, the unimaginable and unexpected wealth of strategic knowledge its missions have generated about Earth, the Universe, and our local Solar System boggles the mind and serves as a legacy of knowledge for Educators to inspire future generations.