Kathryn Elspeth Fishbaugh

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.

North polar region of Mars: Topography of circumpolar deposits from Mars Orbiter Laser Altimeter (MOLA) data and evidence for asymmetric retreat of the polar cap

We have used high-resolution Mars Orbiter Laser Altimeter (MOLA) data to analyze the topography, morphology, stratigraphy, and geologic history of the Martian north circumpolar deposits. The present polar deposits are offset about toward 0°W from the rotational pole. An arc of irregular topography, concentric to Olympia Planitia and the cap, consists of polar material remnants, depressions which we interpret to be kettles, frost-covered and residual ice-filled craters, and frost patches. Olympia Planitia, originally thought to be a flat, sand-covered plain, is characterized by a convex-upward topography, contiguous with the polar cap. We interpret Olympia Planitia to represent a now dune-covered extension of the polar materials. Together, Olympia Planitia and the outlying deposits delineate a former extent of the polar cap. Topographic data have clarified relationships among the circumpolar deposits. Contributors to these deposits include local volcanics, fluvial and aqueous sediments (from outflow channels and a possible standing body of water), pyroclastic ash, sublimation lag from the Olympia Lobe, and eolian-reworked materials. Significant events in the history of the region include (1) formation of the northern lowlands; (2) emplacement of volcanic plains, fluvial and aqueous sedimentation, and subsequent desiccation, forming polygonal patterns which in part underlie the present polar layered deposits; (3) formation of the polar cap, composed primarily of layered deposits; (4) asymmetric retreat of the Olympia Lobe, resulting in sublimation lag deposits, polar remnants, and kettles; and (5) continued collection and reworking of sediments by eolian processes. The cause of the asymmetrical retreat of the Olympia Lobe is unknown.

The construction of Chasma Boreale on Mars

The polar layered deposits of Mars contain the planet’s largest known reservoir of water ice and the prospect of revealing a detailed Martian palaeoclimate record, but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits (NPLD) are unclear, despite decades of debate. Stratigraphic analyses of the exposed portions of Chasma Boreale—a large canyon 500 km long, up to 100 km wide, and nearly 2 km deep—have led most researchers to favour an erosional process for its formation following initial NPLD accumulation. Candidate mechanisms include the catastrophic outburst of water, protracted basal melting, erosional undercutting, aeolian downcutting and a combination of these processes. Here we use new data from the Mars Reconnaissance Orbiter to show that Chasma Boreale is instead a long-lived, complex feature resulting primarily from non-uniform accumulation of the NPLD. The initial valley that later became Chasma Boreale was matched by a second, equally large valley that was completely filled in by subsequent deposition, leaving no evidence on the surface to indicate its former presence. We further demonstrate that topography existing before the NPLD began accumulating influenced successive episodes of deposition and erosion, resulting in most of the present-day topography. Long-term and large-scale patterns of mass balance achieved through sedimentary processes, rather than catastrophic events, ice flow or highly focused erosion, have produced the largest geomorphic anomaly in the north polar ice of Mars.

Crater population and resurfacing of the Martian north polar layered deposits

Present-day accumulation in the north polar layered deposits (NPLD) is thought to occur via deposition on the north polar residual cap. Understanding current mass balance in relation to current climate would provide insight into the climatic record of the NPLD. To constrain processes and rates of NPLD resurfacing, a search for craters was conducted using images from the Mars Reconnaissance Orbiter Context Camera. One hundred thirty craters have been identified on the NPLD, 95 of which are located within a region defined to represent recent accumulation. High Resolution Imaging Science Experiment images of craters in this region reveal a morphological sequence of crater degradation that provides a qualitative understanding of processes involved in crater removal. A classification system for these craters was developed based on the amount of apparent degradation and infilling and where possible depth/diameter ratios were determined. The temporal and spatial distribution of crater degradation is interpreted to be close to uniform. Through comparison of the size-frequency distribution of these craters with the expected production function, the craters are interpreted to be an equilibrium population with a crater of diameter D meters having a lifetime of ~30.75D^(1.14) years. Accumulation rates within these craters are estimated at 7.2D^(−0.14) mm/yr, which corresponds to values of ~3–4 mm/yr and are much higher than rates thought to apply to the surrounding flat terrain. The current crater population is estimated to have accumulated in the last ~20 kyr or less.

Geology and Habitability of Terrestrial Planets

Introduction: A Multidisciplinary Approach to Habitability.- The Geology and Habitability of Terrestrial Planets: Fundamental Requirements for Life.- Emergence of a Habitable Planet.- Creating Habitable Zones, at all Scales, from Planets to Mud Micro-Habitats, on Earth and on Mars.- Conversations on the Habitability of Worlds: The Importance of Volatiles.- Water, Life, and Planetary Geodynamical Evolution.- to Chapter 6: Planetary/Sun Interactions.- A Comparative Study of the Influence of the Active Young Sun on the Early Atmospheres of Earth, Venus, and Mars.- Planetary Magnetic Fields and Solar Forcing: Implications for Atmospheric Evolution.- Planetary Magnetic Dynamo Effect on Atmospheric Protection of Early Earth and Mars.- Epilogue: The Origins of Life in the Solar System and Future Exploration.

Impact cratering in the solar system

Given that impact cratering is the most common geological process in the solar system, study of this topic provides an excellent means of interplanetary comparison. One can gain insight into the crustal properties of various solar system bodies, the population of asteroids and comets that potentially could cause impacts, and the varied ways in which impact cratering has influenced the geologic histories of the planets. The First International Conference on Impact Cratering in the Solar System recently was held at the 40th ESLAB (European Space Laboratory) Symposium at the European Space Agencys European Space Research and Technology Centre, in Noordwijk, the Netherlands. About 150 participants from around the world came to discuss the latest understanding of and issues related to impact cratering in the solar system. The uniqueness of this conference lay in its broad scope, covering everything from the late heavy bombardment controversy to impact-induced mass extinctions. Thus, the conference brought together many scientists of varying expertise who may otherwise have never interacted.