Martian Geomorphology: Introduction

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Martian Geomorphology: introduction

M. R. BALME1*, A. S. BARGERY2, C. J. GALLAGHER3 & S. GUPTA4 1Department of Earth Science, Open University, Walton Hall, Milton Keynes MK7 6AA, UK 2Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, UK 3UCD School of Geography, Planning and Environmental Policy, Newman Building, University College Dublin, Belfield, Dublin 4, Ireland 4Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2PB, UK *Corresponding author (e-mail: [email protected])

This book concerns the Martian landscape; that of geochemistry and age determination (among collection of volcanoes, valleys, impact craters and others), awaits future missions, funding and new ice caps that recent images reveal both to be strik- technology. ingly familiar but also strangely alien to the surface This lack of in situ data, combined with issues of of our own planet. The primary aim of studying pla- equifinality (or convergence of form wherein similar netary landscapes is to understand the process(es) landforms are created by dissimilar processes), by which they formed, with the larger goal of unra- presents a challenge to Martian geomorphological velling key questions about the origin, evolution and interpretations. Thus, we must be circumspect potential habitability of our solar system. when linking form to process, and must highlight Compared with Earth, Mars’ surface erosion where and when more than one working hypothesis rates are extremely low (Golombek & Bridges exists. These challenges are not insurmountable, 2000), so Martian landscapes ranging in age from and we suggest that the number of viable hypotheses the very ancient to the recent still remain preserved decreases as the breadth of data types increases, and and amenable to observation. Because so much of as their spatial resolution improves. For example, the planet’s geological history remains visible, recent and ongoing orbiting missions, including Martian geomorphology has the potential to pro- Mars Global Surveyor, Mars Odyssey, Mars vide even deeper insights into the early evolution Express and Mars Reconnaissance Orbiter, are gen- of the planet than is the case for terrestrial geomor- erating a vast quantity of visible-light, near-infrared phology. Furthermore, the lack of precipitation (at and thermal spectral data that allow researchers to least for much of Martian geological history: characterize the surface texture and composition Craddock & Howard 2002), vegetation or human of Mars in evermore spectacular detail. With the influence have preserved landforms on the surface 30 cm per pixel imaging data from the HiRISE of Mars that on Earth are obscured, degraded or (High Resolution Imaging Science Experiment) buried, and only recognizable from interpretation camera (McEwen et al. 2007) located on board the of the sedimentary rock record. These observations, Mars Reconnaissance Orbiter, we are now able to together with the fact that virtually all of the geo- subject competing hypotheses to closer and closer logical processes seen on Earth are believed to scrutiny until the weight of consilient evidence for have also occurred on Mars, make it a powerful one hypothesis brings it to the fore. laboratory for comparative studies of geomorpholo- On Mars, geomorphological analysis also lays gical processes. the groundwork for future targeted studies. Areas Like any dominantly remote-sensing approach, of Mars that the planetary community identifies as studies of the Martian surface must account for being of particularly high interest have the potential in situ data, but outcrop and hand-sample examin- to eventually become the destinations for in situ ation is a luxury afforded to only a few locations missions. A good example of this is the Mars on Mars and then only through robotic missions. Exploration Rover mission Opportunity (Squyres Similarly, the meteorite samples from Mars are et al. 2004) that was sent to the Terra Meridiani few in number (Meyer 2009) and also lack infor- region largely on the strength of orbital spec- mation on their source location. Targeted sample troscopy observations of enhanced concentrations return, for the examination of thin sections, analysis of the mineral hematite and its association with

From:Balme, M. R., Bargery, A. S., Gallagher,C.J.&Gupta, S. (eds) Martian Geomorphology. Geological Society, London, Special Publications, 356, 1–3. DOI: 10.1144/SP356.1 0305-8719/11/$15.00 # The Geological Society of London 2011. Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

2 M. R. BALME ET AL. specific surface morphologies (Christensen et al. for Martian periglacial domains. Hauber et al. 2000). The mission found evidence of an ancient note that, although the two climates are different, groundwater table within aeolian sandstones – the landforms assemblages are closely matched. providing an explanation for the remotely sensed They conclude that the Martian mid-latitudes are interpretation that the hematite formed in the pres- evolving along the same lines as Svalbard, although ence of water (Squyres et al. 2009). While field much more slowly. Chapter 8 presents a ‘drier’ take trips such as this take a little more money and a on ice in the Martian near-surface, as Mangold little more time than most such expeditions on reviews landforms on Mars thought to have Earth, they are the natural end result of the process formed by sublimation of ice, rather than of thaw. that began with remotely sensed geomorphological Chapters 9 and 10 discuss Martian ‘gullies’, observations and analysis, and the development fluvial-like chutes and debris aprons first discovered and testing of multiple working hypotheses. in 2000 (Malin & Edgett 2000), and which heralded The chapters of this Special Publication include new interest in the concept of geologically recent examples both of the analysis of new datasets and liquid water flowing on the Martian surface. In the application of methodologies new to Mars Chapter 9 Aston et al. use a morphological classi- science. Chapter 2, by Bargery et al., provides fication of gullies to demonstrate that two or context for readers new to Mars by presenting more generations of gully formation occurred. In some background material on Martian geology, Chapter 10 Conway et al. present a methodology climate and exploration. In Chapter 3 Murray & that until now has not been applied to Mars by Illiff’s updated mapping of Mars’ larger moon, using a combination of slope-area and cumulative- Phobos, sheds new light on an ongoing debate: the area distribution analyses of very-high-resolution work uses new images from the High Resolution digital elevation models (DEMs). This is the type Stereo Camera (HRSC) on the European Space of work that has only become possible with the Agency’s (ESA’s) Mars Express spacecraft to con- advent of approximately 30 cm per pixel stereo strain the origin of Phobos’ enigmatic grooves. imaging data provided by NASA’s HiRISE instru- Chapters 4–12 of this Special Publication cover ment. Larger and older flows are discussed in various aspects of the influence of water in the Chapters 11 and 12. In Chapter 11 Balme et al. Martian near-surface. Ice and water are most cer- discuss catastrophic flood channel evolution in the tainly a ‘hot topic’ in Mars science, and one natu- Elysium Planitia region of Mars, while in Chapter rally reflected by the number of papers on that 12 Towner et al. consider whether sinuous channels theme in this volume. Of particular interest is the associated with volcanic landscapes in the Sucii question of whether the Martian climate has gener- Gordi region of Mars were carved by water or lava. ally been too cold to allow thaw or whether melting The final two chapters of the book look at even of near-surface ice has been a geomorphologically more ancient Martian landscapes. In Chapter 13 important process; in other words, what has the Kneissl et al. investigate the origin and erosion balance been between landscapes dominated by rate and style of the Tenuis Rupes – a distinctive sublimation and landscapes dominated by thaw? morphological unit that underlies the north polar In Chapter 4 van Gasselt et al. discuss the evolution cap. They use an exhaustive array of data, combin- of lobate debris aprons in the northern mid- ing observations of morphology, topography from latitude Tempe Terra region. These landforms are the Mars Orbiter Laser Altimeter (MOLA) instru- thought to have formed by creep of rock–ice ment and shallow ground-penetrating RADAR. mixtures. In Chapter 5 Rossi et al. find evidence Finally, in Chapter 14, Sowe et al. compare the for a suite of glacial and periglacial landforms in geomorphology and mineralogy of Interior Layer the southern mid-latitude Thaumasia Highlands. In Deposits, multi-kilometre-scale stacks of strata both of these chapters evidence is presented that that occur in settings such as canyons, jumbled these landforms have been evolving over at least ‘chaos’ terrain and larger impact craters. They con- hundreds of millions of years, and that they might clude that layered mounds in chaos terrains and still be active today. This is, perhaps, a reflection within the Vallis Marineris canyon system have of periodic climate change driven by the extreme similar origins and underwent similar post- variations in axial tilt that Mars undergoes (Laskar depositional weathering processes. et al. 2004). In Chapter 6 Gallagher et al. present very-high- The production of this Special Publication was made poss- resolution imaging data of high-latitude northern ible by the support afforded to the editors by the following agencies: M.R. Balme was supported by an ‘Aurora’ impact craters, and describe geologically young Research Fellowship awarded by the UK Science and patterned grounds and lobate hillslope features Technologies Facilities Council (STFC): and S. Gupta that point to a thaw origin. In Chapter 7 Hauber was supported by a UK STFC Astronomy Standard et al. present a synthesis of terrestrial observations Grant and a UK Royal Society/Leverhulme Trust Senior made in Svalbard that can serve as an analogue Research fellowship. Downloaded from http://sp.lyellcollection.org/ by guest on September 24, 2021

INTRODUCTION 3

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