Geology topics

P.B. James

Publications and source records attributed to P.B. James.

6 recordsLinked to original sources

USGS2001

Mars Color Imager (MARCI) on the Mars Climate Orbiter

The Mars Color Imager, or MARCI, experiment on the Mars Climate Orbiter (MCO) consists of two cameras with unique optics and identical focal plane assemblies (FPAs), Data Acquisition System (DAS) electronics, and power supplies. Each camera is characterized by small physical size and mass (∼6×6×12 cm, including baffle; <500 g), low power requirements (<2.5 W, including power supply losses), and high science performance (1000×1000 pixel, low noise). The Wide Angle (WA) camera will have the capability to map Mars in five visible and two ultraviolet spectral bands at a resolution of better than 8 km/pixel under the worst case downlink data rate. Under better downlink conditions the WA will provide kilometer-scale global maps of atmospheric phenomena such as clouds, hazes, dust storms, and the polar hood. Limb observations will provide additional detail on atmospheric structure at 1/3 scale-height resolution. The Medium Angle (MA) camera is designed to study selected areas of Mars at regional scale. From 400 km altitude its 6° FOV, which covers ∼40 km at 40 m/pixel, will permit all locations on the planet except the poles to be accessible for image acquisitions every two mapping cycles (roughly 52 sols). Eight spectral channels between 425 and 1000 nm provide the ability to discriminate both atmospheric and surface features on the basis of composition. The primary science objectives of MARCI are to (1) observe Martian atmospheric processes at synoptic scales and mesoscales, (2) study details of the interaction of the atmosphere with the surface at a variety of scales in both space and time, and (3) examine surface features characteristic of the evolution of the Martian climate over time. MARCI will directly address two of the three high-level goals of the Mars Surveyor Program: Climate and Resources. Life, the third goal, will be addressed indirectly through the environmental factors associated with the other two goals.

Journal of Geophysical Research E: Planets↗

USGS2000

The 1997 Spring Regression of the Martian South Polar Cap: Mars Orbiter Camera Observations

The Mars Orbiter cameras (MOC) on Mars Global Surveyor observed the south polar cap of Mars during its spring recession in 1997. The images acquired by the wide angle cameras reveal a pattern of recession that is qualitatively similar to that observed by Viking in 1977 but that does differ in at least two respects. The 1977 recession in the 0 o to 120 o longitude sector was accelerated relative to the 1997 observations after LS = 240 o ; the Mountains of Mitchel also detached from the main cap earlier in 1997. Comparison of the MOC images with Mars Orbiter Laser Altimeter data shows that the Mountains of Mitchel feature is controlled by local topography. Relatively dark, low albedo regions well within the boundaries of the seasonal cap were observed to have red-to-violet ratios that characterize them as frost units rather than unfrosted or partially frosted ground; this suggests the possibility of regions covered by CO 2 frost having different grain sizes.

Icarus↗

USGS2000

The state and future of Mars polar science and exploration

As the planet's principal cold traps, the martian polar regions have accumulated extensive mantles of ice and dust that cover individual areas of ∼10 6 km 2 and total as much as 3–4 km thick. From the scarcity of superposed craters on their surface, these layered deposits are thought to be comparatively young—preserving a record of the seasonal and climatic cycling of atmospheric CO 2 , H 2 O, and dust over the past ∼10 5 –10 8 years. For this reason, the martian polar deposits may serve as a Rosetta Stone for understanding the geologic and climatic history of the planet—documenting variations in insolation (due to quasiperiodic oscillations in the planet's obliquity and orbital elements), volatile mass balance, atmospheric composition, dust storm activity, volcanic eruptions, large impacts, catastrophic floods, solar luminosity, supernovae, and perhaps even a record of microbial life. Beyond their scientific value, the polar regions may soon prove important for another reason—providing a valuable and accessible reservoir of water to support the long-term human exploration of Mars. In this paper we assess the current state of Mars polar research, identify the key questions that motivate the exploration of the polar regions, discuss the extent to which current missions will address these questions, and speculate about what additional capabilities and investigations may be required to address the issues that remain outstanding.

Icarus↗

USGS2000

North-south geological differences between the residual polar caps on Mars

Polar processes can be sensitive indicators of global climate, and the geological features associated with polar ice caps can therefore indicate evolution of climate with time. The polar regions on Mars have distinctive morphologic and climatologic features: thick layered deposits, seasonal CO2 frost caps extending to mid latitudes, and near-polar residual frost deposits that survive the summer. The relationship of the seasonal and residual frost caps to the layered deposits has been poorly constrained, mainly by the limited spatial resolution of the available data. In particular, it has not been known if the residual caps represent simple thin frost cover or substantial geologic features. Here we show that the residual cap on the south pole is a distinct geologic unit with striking collapse and erosional topography; this is very different from the residual cap on the north pole, which grades into the underlying layered materials. These findings indicate that the differences between the caps are substantial (rather than reflecting short-lived differences in frost cover), and so support the idea of long-term asymmetry in the polar climates of Mars.

Nature↗

USGS1999

Bright dunes on mars

Seasonal changes observed on the surface of Mars can in part be attributed to the transport of geological materials by wind. Images obtained by orbiting spacecraft in the 1970s showed large wind-formed features such as dunes, and revealed regional time-varying albedos that could be attributed to the effects of dust erosion and deposition. But the resolution of these images was insufficient to identify different types and sources of aeolian materials, nor could they reveal aeolian deposits other than large dunes or extensive surface coverings that were redistributed by dust storms. Here we present images of Mars with up to 50 times better resolution. These images show that martian dunes include at least two distinct components, the brighter of which we interpret to be composed of relatively soft minerals, possibly sulphates. We also find large areas of the martian surface that have several metres or more of aeolian mantle lacking obvious bedforms.

Nature↗

USGS1998

Early views of the Martian surface from the Mars Orbiter Camera of Mars Global Surveyor

High-resolution images of the martian surface at scales of a few meters show ubiquitous erosional and depositional eolian landforms. Dunes, sandsheets, and drifts are prevalent and exhibit a range of morphology, composition (inferred from albedo), and age (as seen in occurrences of different dune orientations at the same location). Steep walls of topographic depressions such as canyons, valleys, and impact craters show the martian crust to be stratified at scales of a few tens of meters. The south polar layered terrain and superposed permanent ice cap display diverse surface textures that may reflect the complex interplay of volatile and non-volatile components. Low resolution regional views of the planet provide synoptic observations of polar cap retreat, condensate clouds, and the lifecycle of local and regional dust storms.

Science↗