B. J. Thomson

Paleoclimate of Mars as captured by the stratigraphic record in Gale Crater

A kilometers-thick sedimentary sequence in Gale Crater exhibits stratigraphic changes in lithology that are consistent with transitions in aqueous and climatic conditions purported to be global in scale. The sequence is divided into two formations, where the Lower formation exhibits a net transition in mineralogy from clay/sulfate to sulfate/oxide assemblages and is separated from the overlying Upper formation by an erosional unconformity. Superposition and crater counts suggest strata in the Lower formation lie along the Noachian-Hesperian time-stratigraphic boundary, whereas beds in the Upper formation, which lack signatures indicative of clay minerals or sulfates, are thinner, more regularly spaced, and clearly younger. The observed stratigraphic trends are consistent with the rocks at Gale Crater recording a global transition from a climate favorable to clay mineral formation to one more favorable to forming sulfates and other salts.

A Closer Look at Water-Related Geologic Activity on Mars

Water has supposedly marked the surface of Mars and produced characteristic landforms. To understand the history of water on Mars, we take a close look at key locations with the High-Resolution Imaging Science Experiment on board the Mars Reconnaissance Orbiter, reaching fine spatial scales of 25 to 32 centimeters per pixel. Boulders ranging up to ∼2 meters in diameter are ubiquitous in the middle to high latitudes, which include deposits previously interpreted as finegrained ocean sediments or dusty snow. Bright gully deposits identify six locations with very recent activity, but these lie on steep (20° to 35°) slopes where dry mass wasting could occur. Thus, we cannot confirm the reality of ancient oceans or water in active gullies but do see evidence of fluvial modification of geologically recent mid-latitude gullies and equatorial impact craters.

Planet-wide sand motion on Mars

Prior to Mars Reconnaissance Orbiter data, images of Mars showed no direct evidence for dune and ripple motion. This was consistent with climate models and lander measurements indicating that winds of sufficient intensity to mobilize sand were rare in the low-density atmosphere. We show that many sand ripples and dunes across Mars exhibit movement of as much as a few meters per year, demonstrating that Martian sand migrates under current conditions in diverse areas of the planet. Most motion is probably driven by wind gusts that are not resolved in global circulation models. A past climate with a thicker atmosphere is only required to move large ripples that contain coarse grains.

Hydrothermal formation of Clay-Carbonate alteration assemblages in the Nili Fossae region of Mars

Abstract The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has returned observations of the Nili Fossae region indicating the presence of Mg-carbonate in small (

Drilling in extreme environments : penetration and sampling on Earth and other planets

1 Introduction 2 Principles of Drilling and Excavation 3 Ground Drilling and Excavation 4 Ice Drilling and Coring 5 Underwater Drilling 6 Extraterrestrial Drilling and Excavation 7 Planetary Sample Acquisition, Handling and Processing 8 Instruments for In-Situ Sample Analysis 9 Contamination and Planetary Protection 10 Conclusions

Crater degradation on the lunar maria: Topographic diffusion and the rate of erosion on the Moon

Landscape evolution on the Moon is dominated by impact cratering in the post-maria period. In this study, we mapped 800 m to 5 km diameter craters on >30% of the lunar maria and extracted their topographic profiles from digital terrain models created using the Kaguya Terrain Camera. We then characterized the degradation of these craters using a topographic diffusion model. Because craters have a well-understood initial morphometry, these data provide insight into erosion on the Moon and the topographic diffusivity of the lunar surface as a function of time. The average diffusivity we calculate over the past 3 Ga is ~5.5 m2/Myr. With this diffusivity, after 3 Ga, a 1 km diameter crater is reduced to approximately ~52% of its initial depth and a 300 m diameter crater is reduced to only ~7% of its initial depth, and craters smaller than ~200–300 m are degraded beyond recognition. Our results also allow estimation of the age of individual craters on the basis of their degradation state, provide a constraint on the age of mare units, and enable modeling of how lunar terrain evolves as a function of its topography.

Utopia Basin, Mars: Characterization of topography and morphology and assessment of the origin and evolution of basin internal structure

Recently obtained Mars Orbiter Laser Altimeter (MOLA) topography has permitted a new assessment of the morphology, structure, and history of Utopia Planitia. The new topographic data convincingly demonstrate that the Utopia region is an impact basin, as originally proposed by McGill [1989], whose major topographic expression is a circular, 1–3 km deep depression ∼3200 km in diameter. Utopia Basin is the largest easily recognizable impact structure in the northern hemisphere of Mars and is the only portion of the northern lowlands that exhibits a distinct large-scale impact signature; its presence there and its ancient age verify that a significant part of the northern lowlands dates back to the Noachian period. Using slope maps derived from gridded topography, we have mapped a series of linear slope anomalies within the basin and have analyzed their origin. These features can be classified into two groups: one oriented dominantly radial to the basin and the other oriented dominantly circumferential. The circumferential features are tens of kilometers wide and hundreds of kilometers long and appear to remain relatively constant with respect to elevation. We explore end-member hypotheses (1) that the features formed by the direct action of water/ice or (2) that they are tectonic wrinkle ridges. We interpret the majority of these features to be due to tectonic deformation (primarily wrinkle-ridge formation), modified by later sedimentation associated with the emplacement of the outflow channels and the formation of the Vastitas Borealis Formation. On the basis of the characteristics of these features and their association with polygonal terrain, thumbprint terrain, smoothness of units, and evidence of sedimentary deposits, we find that our results support earlier hypotheses proposing that a significant volume of water occupied Utopia Basin during the late Hesperian period of outflow channel formation. Utopia Basin differs significantly in depth and degradation state from the deeper and fresher-appearing Hellas Basin, although the two are both Noachian in age. A significant part of this difference seems reasonably interpreted to be the result of the extensive sedimentary and volcanic infilling history of the northern lowlands.

Brazilian Analog for Ancient Marine Environments on Mars

Banded iron formations (BIFs) are iron oxide- and silica-rich chemical sedimentary rocks that were deposited in great abundance during an approximately 800-million-year span from the late Archean to the mid-Proterozoic eons (circa 2.7–1.9 billion years ago). At that time, the terrestrial atmosphere was changing in composition from early anoxic conditions to a more oxygenated state, due possibly to the increasing activity of photosynthetic organisms. It has been suggested that Mars and Earth were more similar in their early history than they are today, and that analogous geologic processes—including those responsible for BIF deposition—may have operated on both planets. Here we discuss BIF samples collected from drill cores at Carajas, Brazil, that represent a variety of fresh, weathered, and altered rocks. Laboratory and remote sensing measurements of these rocks show unique properties that may assist in the discovery of any similar deposits on Mars.

Principles of Drilling and Excavation

1 Introduction 2 Principles of Drilling and Excavation 3 Ground Drilling and Excavation 4 Ice Drilling and Coring 5 Underwater Drilling 6 Extraterrestrial Drilling and Excavation 7 Planetary Sample Acquisition, Handling and Processing 8 Instruments for In-Situ Sample Analysis 9 Contamination and Planetary Protection 10 Conclusions

Identifying cryptotephra units using correlated rapid, nondestructive methods: VSWIR spectroscopy, X‐ray fluorescence, and magnetic susceptibility

This is the publisher’s final pdf. The article is copyrighted by the American Geophysical Union and published by John Wiley & Sons, Inc. It can be found at: http://agupubs.onlinelibrary.wiley.com/agu/journal/10.1002/%28ISSN%291525-2027/