We report the discovery of grooves in Galileo high-resolution images of Gaspra. These features, previously seen only on Mars' satellite Phobos, are most likely related to severe impacts. Grooves on Gaspra occur as linear and pitted depressions, typically 100-200 m wide, 0.8 to 2.5 km long, and 10-20 m deep. Most occur in two major groups, one of which trends approximately parallel to the asteroid's long axis, but is offset by some 15°; the other is approximately perpendicular to this trend. The first of these directions falls along a family of planes which parallel three extensive flat facets identified by Thomas et al., Icarus 107. The occurrence of grooves on Gaspra is consistent with other indications (irregular shape, cratering record) that this asteroid has evolved through a violent collisional history. The bodywide congruence of major groove directions and other structural elements suggests that present-day Gaspra is a globally coherent body.
Magellan images reveal surface features on Venus attributed to wind processes. Sand dunes, wind-sculpted hills, and more than 5830 wind streaks have been identified. The streaks serve as local "wind vanes," representing wind direction at the time of streak formation and allowing the first global mapping of near-surface wind patterns on Venus. Wind streaks are oriented both toward the equator and toward the west. When streaks associated with local transient events, such as impact cratering, are deleted, the westward component is mostly lost but the equatorward component remains. This pattern is consistent with a Hadley circulation of the lower atmosphere.
A visible atmospheric optical depth of 0.9 was measured by the Spirit rover at Gusev crater and by the Opportunity rover at Meridiani Planum. Optical depth decreased by about 0.6 to 0.7% per sol through both 90-sol primary missions. The vertical distribution of atmospheric dust at Gusev crater was consistent with uniform mixing, with a measured scale height of 11.56 +/- 0.62 kilometers. The dust's cross section weighted mean radius was 1.47 +/- 0.21 micrometers (mm) at Gusev and 1.52 +/- 0.18 mm at Meridiani. Comparison of visible optical depths with 9-mm optical depths shows a visible-to-infrared optical depth ratio of 2.0 +/- 0.2 for comparison with previous monitoring of infrared optical depths.
Wind‐related features observed by the rover Spirit in Gusev crater, Mars, include patches of soil on the surface, some of which are organized into bed forms. Windblown grains include dust (inferred to be <3 μm in diameter), sands (up to a few hundred μm in diameter), and granules (>2 mm in diameter). Microscopic Imager data show the sands and granules to be rounded and relatively spherical, typical of grains transported long distances by the wind. The interior of bed forms exposed by rover operations suggests the infiltration of dust among the grains, indicating that these sands are not currently experiencing saltation. Orientations of 1520 features (such as bed forms and ventifacts) along Spirit's traverse from the landing site (the Columbia Memorial Station) to West Spur in the Columbia Hills suggest primary formative winds from the north‐northwest, which correlate with measurements of features seen in orbiter images and is consistent with afternoon winds predicted by atmospheric models. A secondary wind from the southeast is also suggested, which correlates with predictions for nighttime/early morning winds. Wind abrasion is indicated by ventifacts in the form of facets and grooves cut into rocks, the orientations of which also indicate prevailing winds from the north‐northwest. Orientations of many aeolian features in the West Spur area, however, have more scatter than elsewhere along the traverse, which is attributed to the influence of local topography on the patterns of wind. Active dust devils observed on the floor of Gusev from the Columbia Hills demonstrate that dust is currently mobile. Sequential images of some dust devils show movement as rapid as 3.8 m/s, consistent with wind velocities predicted by atmospheric models for the afternoon, when most of the dust devils were observed. Sands accumulated on the rover deck in the same period suggest that some sands in the Columbia Hills experience active saltation. “Two‐toned” rocks having a light band coating at their bases are considered to represent partial burial by soils and subsequent exposure, while “perched” rocks could represent materials lowered onto other rocks by deflation of supporting soils. Measurements of the heights of the light bands and the perched rocks range from <1 cm to 27 cm, indicating local deflation by as much as 27 cm.
Ejecta with flow features and discrete termini surround many fresh Martian craters. Several morphologies of the flow-like ejecta are observed; they are found globally and in nearly all terrains. It is suggested that the morphology of flow ejecta craters is related to the amount of subsurface volatiles and/or to atmospheric drag effects. It was attempted to constrain factors which could contribute to the ejecta morphology such as latitude, elevation, and terrain unit, however, they involved only one or two constrained variables or used global data sets based on Mariner 9 information. Viking-based data sets are becoming available and may provide a better base from which an understanding of the factors which governs ejecta morphology may be obtained. Block sizes of Martian flow ejecta may provide clues to the ejecta emplacement process.
Research Article| July 01, 1989 Shuttle radar images of wind streaks in the Altiplano, Bolivia Ronald Greeley; Ronald Greeley 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Search for other works by this author on: GSW Google Scholar Philip Christensen; Philip Christensen 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Search for other works by this author on: GSW Google Scholar Raul Carrasco Raul Carrasco 2Servicio Geológico de Bolivia, La Paz, Bolivia Search for other works by this author on: GSW Google Scholar Author and Article Information Ronald Greeley 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Philip Christensen 1Department of Geology, Arizona State University, Tempe, Arizona 85287 Raul Carrasco 2Servicio Geológico de Bolivia, La Paz, Bolivia Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1989) 17 (7): 665–668. https://doi.org/10.1130/0091-7613(1989)017<0665:SRIOWS>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation Ronald Greeley, Philip Christensen, Raul Carrasco; Shuttle radar images of wind streaks in the Altiplano, Bolivia. Geology 1989;; 17 (7): 665–668. doi: https://doi.org/10.1130/0091-7613(1989)017<0665:SRIOWS>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Shuttle imaging radar (SIR-A) coverage across Bolivia shows the major physiographic provinces, including the Andean Altiplano. The Altiplano contains a variety of eolian features, many of which are visible as radar-dark, radar-mottled, and radar-bright streaks aligned parallel to the prevailing winds. The streaks form downwind from hills and are as much as 15 km long and 800 m wide. Dark streaks originate between closely spaced hills, whereas bright streaks form in the immediate lee of hills. The radar brightness of the streaks is modulated by the proportion of sand cover, vegetation, and exposed substrate, all of which relate to the local wind regime. In the radar-dark streaks, vegetation is sparse and the sand is organized into dune forms, some of which can be recognized as barchan dunes on the radar image by outlining of the dark dune by bright substrate. Radar-mottled zones are covered by numerous 0.5-2-m-high coppice dunes, and in radarbright streaks, the sand forms flat sheets but also includes sand mounds and abundant vegetation. Measurements indicate that winds are strongest and most turbulent in the region of active sand sheets and dunes, inhibiting the growth of vegetation and the formation of mounds and resulting in a radar-dark zone. These results are consistent with previous studies that have demonstrated the existence of turbulent eddies in the wake of topographic obstacles that produce zones of increased surface wind shear and enhanced sand mobility. The relation between the radar signature and the wind regime allows inferences to be drawn for the wind regime from image interpretation. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Nearly all major planets and moons in our Solar System have been visited by spacecraft and the data they have returned has revealed the incredible diversity of planetary surfaces. Featuring a wealth of images, this textbook explores the geological evolution of the planets and moons. Introductory chapters discuss how information gathered from spacecraft is used to unravel the geological complexities of our Solar System. Subsequent chapters focus on current understandings of planetary systems. The textbook shows how planetary images and remote sensing data are analyzed through the application of fundamental geological principles. It draws on results from spacecraft sent throughout the Solar System by NASA and other space agencies. Aimed at undergraduate students in planetary geology, geoscience, astronomy and solar system science, it highlights the differences and similarities of the surfaces at a level that can be readily understood by non-specialists.
Any planet or satellite having a dynamic atmosphere and a solid surface has the potential for experiencing aeolian (wind) processes. A survey of the Solar System shows at least four planetary objects which potentially meet these criteria: Earth, Mars, Venus, and possibly Titan, the largest satellite of Saturn. While the basic process is the same among these four objects, the movement of particles by the atmosphere, the aeolian environment is drastically different. It ranges from the hot (730 K), dense atmosphere of Venus to the extremely cold desert (218 K) environment of Mars where the atmospheric surface pressure is only approximately 7.5 mb. In considering aeolian processes in the planetary perspective, all three terrestrial planets share some common areas of attention for research, especially in regard to wind erosion and dust storms. Relevant properties of planetary objects potentially subject to aeolian processes are given in tabular form.
