Geology topics

S. Squyres

Publications and source records attributed to S. Squyres.

9 recordsLinked to original sources

USGS2008

First in situ investigation of a dark wind streak on Mars

Prominent low‐albedo wind streaks issue from embayments at the north end of Victoria crater in Meridiani Planum, the site of surface investigations by the Mars Exploration Rover Opportunity. Opportunity was sent to examine the darkest of these wind streaks and compare it to the adjacent soil in the brighter corridor between the streaks. Two nearby sites inside and outside of the streak were selected for visible and infrared remote sensing and for elemental abundance measurements and images of the microscopic soil morphology. The rover was next sent to study the interaction of the wind streak with an obstacle, a small rock near the source of the streak. Opportunity's observations suggest that the Victoria wind streaks are deposits of basaltic sand blown out of the crater from the dark dunes nestled below the crater rim, particularly at the base of the alcove leading up to the darkest streak. No local sources of sand have been identified within the Victoria crater wall rock, suggesting that the sand is supplied from outside the crater and is presently escaping its temporary topographic trap. This process presents a possible explanation for the serrated margin of Victoria crater through abrasion of the soft rock as trapped sands are blown out of the crater and carve alcoves under various seasonal winds. Some indication of the rate of activity of these wind streaks will be provided by continued monitoring of the erasure of the rover's tracks.

Journal of Geophysical Research E: Planets↗

USGS2008

Hydrothermal processes at Gusev Crater: An evaluation of Paso Robles class soils

The Mars Exploration Rover Spirit analyzed multiple occurrences of sulfur-rich, light-toned soils along its traverse within Gusev Crater. These hydrated deposits are not readily apparent in images of undisturbed soil but are present at shallow depths and were exposed by the actions of the rover wheels. Referred to as 'Paso Robles' class soils, they are dominated by ferric iron sulfates, silica, and Mg-sulfates. Ca-sulfates, Ca-phosphates, and other minor phases are also indicated in certain specific samples. The chemical compositions are highly variable over both centimeter-scale distances and between the widely separated exposures, but they clearly reflect the elemental signatures of nearby rocks. The quantity of typical basaltic soil mixed into the light-toned materials prior to excavation by the rover wheels is minimal, suggesting negligible reworking of the deposits after their initial formation. The mineralogy, geochemistry, variability, association with local compositions, and geologic setting of the deposits suggest that Paso Robles class soils likely formed as hydrothermal and famarolic condensates derived from magma degassing and/ or oxidative alteration of crustal iron sulfide deposits. Their occurrence as unconsolidated, near-surface soils permits, though does not require, an age that is significantly younger than that of the surrounding rocks. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research E: Planets↗

USGS2006

Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 2. Opportunity

The Panoramic Camera (Pancam) on the Mars Exploration Rover Opportunity acquired visible/near‐infrared multispectral observations of soils and rocks under varying viewing and illumination geometries that were modeled using radiative transfer theory to improve interpretations of the microphysical and surface scattering nature of materials in Meridiani Planum. Nearly 25,000 individual measurements were collected of rock and soil units identified by their color and morphologic properties over a wide range of phase angles (0–150°) at Eagle crater, in the surrounding plains, in Endurance crater, and in the plains between Endurance and Erebus craters through Sol 492. Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of local facet orientation estimates. Outcrop rocks overall exhibited the highest single scattering albedos (≤0.9 at 753 nm), and most spherule‐rich soils exhibited the lowest (≤0.6 at 753 nm). Macroscopic roughness among outcrop rocks varied but was typically larger than spherule‐rich soils. Data sets with sufficient phase angle coverage (resulting in well‐constrained Hapke parameters) suggested that models using single‐term and two‐term Henyey‐Greenstein phase functions exhibit a dominantly broad backscattering trend for most undisturbed spherule‐rich soils. Rover tracks and other compressed soils exhibited forward scattering, while outcrop rocks were intermediate in their scattering behaviors. Some phase functions exhibited wavelength‐dependent trends that may result from variations in thin deposits of airfall dust that occurred during the mission.

Journal of Geophysical Research E: Planets↗

USGS2006

Spectrophotometric properties of materials observed by Pancam on the Mars Exploration Rovers: 1. Spirit

Multispectral observations of rocks and soils were acquired under varying illumination and viewing geometries in visible/near‐infrared wavelengths by the Panoramic Camera (Pancam) on the Spirit Mars Exploration Rover to provide constraints on the physical and mineralogical nature of geologic materials in Gusev Crater. Data sets were acquired at six sites located near the landing site, in the surrounding plains, and in the West Spur and Husband Hill regions of the Columbia Hills. From these ∼600 images, over 10,000 regions of interest were selected of rocks and soils over a wide range of phase angles (0–130°). Corrections for diffuse skylight incorporated sky models based on observations of atmospheric opacity throughout the mission. Disparity maps created from Pancam stereo images allowed inclusion of estimates of local facet orientations in the sky models. Single‐term and two‐term phase functions derived from Hapke scattering models exhibit a dominantly broad backscattering trend for soils and “Red” rocks inferred to be covered with variable amounts of dust and other coatings, consistent with the results from the Viking Lander and Imager for Mars Pathfinder cameras. Darker “Gray” rock surfaces (inferred to be relatively less dust covered) display more narrow, forward scattering behaviors, consistent with particles exhibiting little internal scattering. Gray and Red rocks are macroscopically rougher than most soil units, although a “dust‐cleaning” event observed near the Paso Robles site caused an increase in soil surface roughness in addition to a substantial decrease in surface single scattering albedo. Gray rocks near the rim of Bonneville Crater exhibit the largest macroscopic roughness ( ) among all units, as well as the greatest backscattering among Gray rocks. Photometric properties of coated Red rocks vary in the West Spur region, possibly as a result of weathering differences related to elevation‐dependent aeolian regimes.

Journal of Geophysical Research E: Planets↗

USGS2006

Sedimentary textures formed by aqueous processes, Erebus crater Meridiani Planum, Mars

New observations at Erebus crater (Olympia outcrop) by the Mars Exploration Rover Opportunity between sols 671 and 735 (a sol is a martian day) indicate that a diverse suite of primary and penecontemporaneous sedimentary structures is preserved in sulfate-rich bedrock. Centimeter-scale trough (festoon) cross-lamination is abundant, and is better expressed and thicker than previously described examples. Postdepositional shrinkage cracks in the same outcrop are interpreted to have formed in response to desiccation. Considered collectively, this suite of sedimentary structures provides strong support for the involvement of liquid water during accumulation of sedimentary rocks at Meridiani Planum.

Geology↗

USGS2005

An astrobiological perspective on Meridiani Planum

Sedimentary rocks exposed in the Meridiani Planum region of Mars record aqueous and eolian deposition in ancient dune and interdune playa-like environments that were arid, acidic, and oxidizing. On Earth, microbial populations have repeatedly adapted to low pH and both episodic and chronic water limitation, suggesting that, to a first approximation, the Meridiani plain may have been habitable during at least part of the interval when deposition and early diagenesis took place. On the other hand, the environmental conditions inferred for Meridiani deposition would have posed a challenge for prebiotic chemical reactions thought to have played a role in the origin of life on Earth. Orbital observations suggest that the combination of sulfate minerals and hematite found in Meridiani rocks may be unusual on the martian surface; however, there is reason to believe that acidity, aridity, and oxidizing conditions were broadly distributed on ancient Mars. When these conditions were established and how much environmental heterogeneity existed on early Mars remain to be determined. Because sulfates and iron oxides can preserve detailed geochemical records of environmental history as well as chemical, textural and microfossil signatures of biological activity, Meridiani Planum is an attractive candidate for Mars sample return. ?? 2005 Elsevier B.V. All rights reserved.

Earth and Planetary Science Letters↗

USGS2004

Surficial deposits at Gusev crater along Spirit Rover traverses

The Mars Exploration Rover Spirit has traversed a fairly flat, rock-strewn terrain whose surface is shaped primarily by impact events, although some of the landscape has been altered by eolian processes. Impacts ejected basaltic rocks that probably were part of locally formed lava flows from at least 10 meters depth. Some rocks have been textured and/or partially buried by windblown sediments less than 2 millimeters in diameter that concentrate within shallow, partially filled, circular impact depressions referred to as hollows. The terrain traversed during the 90-sol (martian solar day) nominal mission shows no evidence for an ancient lake in Gusev crater.

Science↗

USGS2002

Remotely sensed geology from lander-based to orbital perspectives: Results of FIDO rover May 2000 field tests

Blind field tests of the Field Integration Design and Operations (FIDO) prototype Mars rover were carried out 7-16 May 2000. A Core Operations Team (COT), sequestered at the Jet Propulsion Laboratory without knowledge of test site location, prepared command sequences and interpreted data acquired by the rover. Instrument sensors included a stereo panoramic camera, navigational and hazard-avoidance cameras, a color microscopic imager, an infrared point spectrometer, and a rock coring drill. The COT designed command sequences, which were relayed by satellite uplink to the rover, and evaluated instrument data. Using aerial photos and Airborne Visible and Infrared Imaging Spectrometer (AVIRIS) data, and information from the rover sensors, the COT inferred the geology of the landing site during the 18 sol mission, including lithologic diversity, stratigraphic relationships, environments of deposition, and weathering characteristics. Prominent lithologic units were interpreted to be dolomite-bearing rocks, kaolinite-bearing altered felsic volcanic materials, and basalt. The color panoramic camera revealed sedimentary layering and rock textures, and geologic relationships seen in rock exposures. The infrared point spectrometer permitted identification of prominent carbonate and kaolinite spectral features and permitted correlations to outcrops that could not be reached by the rover. The color microscopic imager revealed fine-scale rock textures, soil components, and results of coring experiments. Test results show that close-up interrogation of rocks is essential to investigations of geologic environments and that observations must include scales ranging from individual boulders and outcrops (microscopic, macroscopic) to orbital remote sensing, with sufficient intermediate steps (descent images) to connect in situ and remote observations.

Journal of Geophysical Research E: Planets↗

USGS2001

Mars Descent Imager (MARDI) on the Mars Polar Lander

The Mars Descent Imager, or MARDI, experiment on the Mars Polar Lander (MPL) consists of a camera characterized by small physical size and mass (∼6×6×12 cm, including baffle; <500 gm), low power requirements (<2.5 W, including power supply losses), and high science performance (1000×1000 pixel, low noise). The intent of the investigation is to acquire nested images over a range of resolutions, from 8 m/pixel to better than 1 cm/pixel, during the roughly 2 min it takes the MPL to descend from 8 km to the surface under parachute and rocket-powered deceleration. Observational goals will include studies of (1) surface morphology (e.g., nature and distribution of landforms indicating past and present environmental processes); (2) local and regional geography (e.g., context for other lander instruments: precise location, detailed local relief); and (3) relationships to features seen in orbiter data. To accomplish these goals, MARDI will collect three types of images. Four small images (256×256 pixels) will be acquired on 0.5 s centers beginning 0.3 s before MPL's heatshield is jettisoned. Sixteen full-frame images (1024×1024, circularly edited) will be acquired on 5.3 s centers thereafter. Just after backshell jettison but prior to the start of powered descent, a “best final nonpowered descent image” will be acquired. Five seconds after the start of powered descent, the camera will begin acquiring images on 4 s centers. Storage for as many as ten 800×800 pixel images is available during terminal descent. A number of spacecraft factors are likely to impact the quality of MARDI images, including substantial motion blur resulting from large rates of attitude variation during parachute descent and substantial rocket-engine-induced vibration during powered descent. In addition, the mounting location of the camera places the exhaust plume of the hydrazine engines prominently in the field of view.

Journal of Geophysical Research E: Planets↗