Dynamic Mars: Recent and Current Landscape Evolution of the Red Planet

By Susan Conway

Dynamic Mars: Recent and Current Landscape Evolution of the Red Planet presents the latest observations, interpretations, and explanations of geological change at the surface or near-surface of this terrestrial body. These changes raise questions about a decades-old paradigm, formed largely in the aftermath of very coarse Mariner-mission imagery in the 1960s, suggesting that much of the interesting geological activity on Mars occurred deep in its past, eons ago. The book includes discussions of (1) Mars’ ever-changing atmosphere and the impact of this on the planet’s surface and near-surface; (2) the possible involvement of water in relatively new, if not contemporary, gully-like flows and slope streaks (i.e. recurring slope lineae); and (3) the identification of a broad suite of agents and processes (i.e. glacial, periglacial, aeolian, meteorological, volcanic, and meteoric) that are actively revising surface and near-surface landscapes, landforms, and features on a local, regional, and hemispheric scale.Highly illustrated and punctuated by data from the most recent Mars missions, Dynamic Mars is a valuable resource for all levels of research in the geological history of Mars, as well as of the three other terrestrial planets.

• Utilizes observational and model-based data as well as geological context to frame the understanding of the dynamic surface and near-surface of Mars
• Presents a broad spectrum of highly regarded experts and themes to discuss and evaluate the geological history of late and current Mars
• Includes extensive and detailed imagery to clearly illustrate these themes, discussions, and evaluations

• Language: English
• Publisher: Elsevier Science
• Release date: Aug 7, 2018
• ISBN: 9780128130193

Book preview

Dynamic Mars

Recent and Current Landscape Evolution of the Red Planet

Editors

Richard J. Soare

Susan J. Conway

Stephen M. Clifford

Table of Contents

Cover image

Title page

Copyright

List of Contributors

Mariners’ Way: Beyond the Future to the Past

Introduction

Section 1. Late Amazonian Epoch Climate

Chapter 1. Orbital (Climatic) Forcing and Its Imprint on the Global Landscape

1.1. Introduction

1.2. Climate Forcing

1.3. Volatile Emplacement

1.4. Morphological Evidence for Recent Climate Change

1.5. Conclusions

Section 2. Recent Surface Water AT/NEAR The Mid-Latitudes?

Chapter 2. Unraveling the Mysteries of Recurring Slope Lineae

2.1. Introduction

2.2. Methods

2.3. Observations

2.4. Discussion

2.5. Mechanisms

2.6. Summary and Implications

Chapter 3. Martian Gullies and Their Connection With the Martian Climate

3.1. Introduction

3.2. Climatic Origins for Martian Gullies

3.3. Approach

3.4. Results and Discussion

3.5. Conclusions

Chapter 4. Late Amazonian–Aged Channel and Island Systems Located East of Olympus Mons, Mars

4.1. Introduction

4.2. Methods and Terminology

4.3. The Northwestern Tharsis Channels and Islands

4.4. Streamlined Forms and Islands

4.5. Ages

4.6. Future Directions

4.7. Conclusions

Section 3. The Polar Regions

Chapter 5. The Exotic Processes Driving Ephemeral Seasonal Surface Change on Mars

5.1. Introduction

5.2. History of Dynamic Mars: From Disk Sketches to High-Resolution Imaging

5.3. High-Latitude Seasonal Processes

5.4. Midlatitude Seasonal Processes

5.5. Low Latitude Seasonal Processes

5.6. Conclusion

Chapter 6. CO2-Driven Geomorphological Processes: Landscape Evolution

6.1. Araneiforms

6.2. Furrows

6.3. New Dendritic Troughs

6.4. Polar Gullies

6.5. Residual Polar Cap Scarp Avalanches

6.6. Degradation of Swiss Cheese Terrain

6.7. Conclusion

Section 4. Glacial and Periglacial Landscapes

Chapter 7. Paleo-Periglacial and Ice-Rich Complexes in Utopia Planitia

7.1. Introduction

7.2. Methods

7.3. Observations

7.4. Periglaciation on Earth

7.5. Geological Conciliation

7.6. A Proposed Periglacial Geochronology

7.7. Conclusions

Chapter 8. Slow Periglacial Mass Wasting (Solifluction) on Mars

8.1. Introduction

8.2. Solifluction on Earth

8.3. Summary of Previous Work on Small-Scale Lobes in the Northern Hemisphere

8.4. Data and Methods

8.5. Key Geomorphological Observations and Interpretations

8.6. Discussion

8.7. Conclusions

Section 5. Volcanism

Chapter 9. Volcanic Disruption of Recent Icy Terrain in the Argyre Basin, Mars

9.1. Introduction

9.2. Observations

9.3. Discussion

Section 6. Aeolian Processes

Chapter 10. Dust Devils: Stirring Up the Martian Surface

10.1. Introduction

10.2. Observations

10.3. Dust Devil Characteristics

10.4. Dust Devil Tracks

10.5. Global Impact

10.6. Summary and Outlook

List of Abbreviations

Chapter 11. Dark Dunes of Mars: An Orbit-To-Ground Multidisciplinary Perspective of Aeolian Science

11.1. Introduction

11.2. Part 1. Geographic Information Science From Orbit

11.3. Geographic Information Science From Orbit—Sand Movement and Sand Types

11.4. Part 2. Eyes From Above: The Landscapes of Gale Crater

11.5. Part 3. Wheels on the Ground: The Bagnold Dunefield

11.6. Future Directions

Section 7. Other Surface-Modification Processes

Chapter 12. Modification of the Martian Surface by Impact Cratering

12.1. Introduction

12.2. Primary Impact Craters

12.3. Secondary Craters

12.4. Discussion

12.5. Conclusions

Chapter 13. Stone Pavements, Lag Deposits, and Contemporary Landscape Evolution

13.1. Introduction

13.2. Classification

13.3. Earth Analog Models

13.4. Gravel Source and Clast-Size Reduction

13.5. Nature of Martian Lag and Stone Pavement Surfaces

13.6. Clast Source and Size Reduction

13.7. Models of Lag Formation on Mars

13.8. A Model of Lag-Dominated Landscape Evolution

13.9. Models of Stone Pavement Formation on Mars

13.10. Conclusions

Chapter 14. Karst Landforms as Markers of Recent Climate Change on Mars: An Example From a Late Amazonian Epoch Evaporate-Karst Within a Trough in Western Noctis Labyrinthus

14.1. Introduction

14.2. Methods

14.3. Study Area

14.4. Morphological and Morphometric Analyses of Noctis Labyrinthus Features

14.5. Discussion

14.6. Conclusions

An Epilogue

Index

Copyright

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ISBN: 978-0-12-813018-6

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Typeset by TNQ Technologies

MAIN IMAGE Slope Monitoring in Hale Crater Central Peaks ESP_049308_1440 credit: NASA/JPL/University of Arizona

FIRST BOX IMAGE New Impact Site Formed Between January 2007 and May 2009 ESP_015949_1795 credit: NASA/JPL/University of Arizona

SECOND BOX IMAGE Gullies on the Dunes of Russell Crater PSP_010446_1255 credit: NASA/JPL/University of Arizona

THIRD BOX IMAGE Spider Morphology ESP_011776_0930 credit: NASA/JPL/University of Arizona

FOURTH BOX IMAGE The Serpent Dust Devil of Mars ESP_026051_2160 credit: NASA/JPL/University of Arizona

List of Contributors

K.-Michael Aye,     University of Colorado at Boulder, Boulder, CO, United States

Davide Baioni,     Università degli Studi di Urbino Carlo Bo, Urbino, Italy

Mark A. Bishop,     Planetary Science Institute Tucson, AZ, United States

Susan J. Conway,     Laboratoire de Planétologie et Géodynamique de Nantes- UMR CNRS 6112, Nantes, France

John C. Dixon,     University of Arkansas, Fayetteville, AR, United States

James M. Dohm,     The University Museum, The University of Tokyo, Tokyo, Japan

Colman J. Gallagher,     University College, Dublin, Ireland

Virginia C. Gulick,     NASA Ames Research Center/SETI Institute, Mountain View, CA, United States

Henrik I. Hargitai,     NASA Ames Research Center/NPP, Moffett Field, CA, United States

Tanya N. Harrison,     School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, United States

Ernst Hauber,     Deutsches Zentrum für Luft- und Raumfahrt (DLR), Berlin, Germany

Harald Hiesinger,     Westfälische Wilhelms-Universität, Münster, Germany

Andreas Johnsson,     University of Gothenburg, Gothenburg, Sweden

Stephen R. Lewis,     Open University, Milton Keynes, United Kingdom

Michael A. Mischna,     Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA

Gordon R. Osinski,     University of Western Ontario, London, ON, Canada

Ganna Portyankina,     LASP/University of Colorado, Boulder, CO, United States

Dennis Reiss,     Westfälische Wilhelms-Universität, Münster, Germany

Frédéric Schmidt,     GEOPS, Univ. Paris-Sud, CNRS, Université Paris-Saclay, Orsay, France

Richard J. Soare,     Dawson College, Montreal, QC, Canada

David E. Stillman,     Southwest Research Institute, Boulder, CO, United States

Jean-Pierre Williams,     University of California, Los Angeles, CA, United States

Mariners’ Way: Beyond the Future to the Past

Richard J. Soare¹, Dorothy Oehler², and Michael Mischna³,     ¹Dawson College, Montreal, QC, Canada,     ²Planetary Science Institute, Tucson, AZ, United States,     ³California Institute of Technology, Pasadena, CA, United States

1. The Future

As Mariner 4 plotted its multimillion mile path through the heavens a little more than 50  years ago, people around the world gazed with wonder and awe at a bright red-pinkish dot in the sky. If all went well on the opening of Mariner’s (camera) eye at 20:24 (EDT), Wednesday, July 14th, 1965, its field of view would encompass: …the brilliant scenery of a Martian ‘oasis’ [possible evidence of intelligently-built structures], three deserts, one of the planets so-called ‘seas’, and perhaps the fringes of the receding south polar cap (Boston Globe [BG], 11-July-65).

Mariner 4 was expected to produce 21 pictures, taken within a total span of 25  min, as the spacecraft raced by Mars on its way to a celestial end somewhere in deep space two and a half years later (Fig. 1). Each of these pictures would require a journey of 134 million miles to reach the Earth and take 8  h and 35  min to do so. Each image would cover a planetary swath 125  miles wide and resolve surface details as small as 1.5  miles in diameter.

As the spacecraft approached Mars, a global audience paused and reflected on questions of the future past. What form of life is considered possible on Mars? Perhaps, some form of primitive vegetation—most likely mosses, lichens, or algae. Perhaps microbial life (BG, 29-Nov-64). What about intelligent life? Is it possible that an animal could have developed there with sufficient intelligence to alter his environment, to evolve a language, to build a civilization? (BG, 4-July-65). If so, then Lowell’s …much discussed canals should appear as thin lines on the surface and the test would be put to…[the] belief that a wiser and older civilization than ours built them to obtain a (seasonally-generated) water supply from polar regions (BG, 3-Jan-65). Seemingly consistent with this belief were Earth-based observations of white caps at the north and south Martian poles waxing and waning with the seasons. Spreading raggedly toward the equator from these caps are vast areas which darken in spring, as if there was vegetation fed by water from the melting polar ice; these oases lie astride of yellow-red deserts that girdle the equator but only where they are intercepted by a network of lines much like the irrigation canals in some of Earth’s deserts (BG, 4-July-65).

After much anticipation, the first grainy black and white picture of Mars was processed and released to the public on the 15th of July 1965 (Fig. 2). It was taken by Mariner 4 at a distance of 10,500  miles, framed an area on the Martian surface that comprised ∼200 miles, and imaged the Desert of Amazonis (BG, 16-July-65). Dr. Robert Leighton, chief of the Mariner television experiment, remarked that it is very hard to see anything in that picture; [however,] we were overjoyed to receive it. It showed Mars was there (BG, 16-July-65). The second and third photographs …resolved details as small as two miles across, as much as 30 times sharper than the best views available through the finest telescopes on Earth (BG, 18-July-65).

Figure 1   NASA base map displaying the location of the images of Mars taken by the Mariner 4 spacecraft, July 14–15, 1964 ( http://www.planetary.org/blogs/emily-lakdawalla/2012/12100800-mariner-4-mars.html ).

From the earliest shots of Mars, Mariner’s gazing eye and probing instrumentation began to dissipate the fog of myth and fanciful speculation that had shrouded the red planet for hundreds of years. For example, Mars’ atmosphere was even thinner than anticipated. Surface pressures seemingly were no higher than 10–20  mbars, equivalent to a mountain range with peaks between 80,000 and 100,000 feet on Earth; 1000  mbars of air pressure support Earth life at sea level (BG, 16-July-65).

Biologically speaking, a thin, oxygen-poor atmosphere also engenders diurnal swings of temperature that are extremely wide and inhospitable; at some locations temperatures rise to 80°F at noon; [however] they plunge to 100°C below zero at midnight (BG, 4-July-65). Moreover: (1) nitrogen, …an essential element to forming the amino acid molecules related to terrestrial life, is…absent from the atmosphere (BG, 18-Jan-73); (2) despite its zones of apparent vegetation, analysis of light from Mars has [not] disclosed a trace of chlorophyll, the green substance in earth plants (BG, 4-July-65); and, 3) Mars’ atmosphere …is mostly carbon dioxide….; [this is] the same compound that dominates the dense [and noxious] atmosphere of the planet Venus. Here, any more so than on Venus, there is no reason to believe that life has or ever did arise (BG, 3-Aug-69).

Figure 2  This is the first close-up image ever taken of Mars by Mariner 4 (1965) (m04_01d, image resolution ∼5   km/pixel). It shows an area about 330   km across by 1200   km (205   miles by 745   miles) from limb to the bottom of the frame, centered at 37   N, 187   W. The area is near the boundary of Elysium Planitia to the west and Arcadia Planitia to the east. North is up. 

Image credit: NASA/JPL-CalTech.

Geologically speaking, evidence that Mars …is radically different from our own Earth and has always been so came in an electronic whisper [with the seventh Mariner 4 photograph]; …more than a dozen well-defined craters [were photographed] in only 32,400 square miles of Martian landscape. That is a concentration of meteorite hits comparable to those our Ranger [probe] spied on the moon (BG, 30-July-65). This suggested that the surfaces of both bodies had been largely unaltered since early in the history of the solar system when impacts large and small were intensely frequent (Fig. 3). At the same time, …evidence that there is or ever has been running springs or running water on Mars was fleeting (BG, 3-Aug-69). Lowell’s canals, for example, consistently …were showing up as indistinct low-contrast blotches, rather than as well-defined sharp features (BG, 3-Aug-69).

On the other hand, some of the images delivered by Mariner 9 in 1971 and 1972 tempered …the picture of a ‘dead’ Mars with a cold interior, [an ancient surface] and a thin, nearly waterless atmosphere (BG, 4-Dec-71). Huge, high craters near the Martian region called Tharsis strongly resemble volcanic features on Earth known as calderas (BG, 4-Dec-71); perhaps this indicates …that Mars underwent less interior heating in its early history than Earth but more than the moon (BG, 4-Dec-71), that Mars may still …have a molten core, that it is still possible that volcanic activity exists (BG, 18-Jan-73) and that temperatures sufficiently elevated for liquid water to be stable at the surface might have been in place at one time, i.e. …numerous sinuous channels with tributaries meandering for hundreds of miles across the planet [were being photographed]. They resemble river beds on Earth, according to Dr. Carl Sagan (Mariner experiment group-leader) (BG, 10-Mar-73). For example, one broad channel extends from the base of a landslide-covered ridge slope [and] looks like it might have been created by sudden floods of water that followed from the melting of ancient glaciers (BG, 18-Jan-73) (Fig. 4). Perhaps Mars was neither as hydrologically inanimate nor as lifeless, at least earlier in its geological history, as the first Mariner images had intimated.

Figure 3  An ancient, eroded impact crater (75   miles in diameter) in the Atlantis region of Sirenum Terrae. North is up. 

Image credit: NASA/JPL-CalTech.

2. The past

Enigmas wrapped in paradoxes shrouded in mystery: Mars…

1. airless and largely arid? currently yes; perhaps not always so

2. geologically dead? seemingly not, depending on the spatial scale and temporal span

3. inhabited? unknown

Absent of boots on the ground and a spade to hand, Dr. Robert Sharp, one of the lead scientists on the Mariner team, lamented the irreconcilability of planetary science practiced from afar with the need for Martian ground truth: we…are in the same boat as a veterinarian trying to understand how a strange elephant feels by studying wrinkles on his skin through high-powered binoculars (BG, 3-Aug-69). Are we any closer to understanding the origin and development of these wrinkles than we were 50  years ago? Only the past will tell….

Figure 4  Nirgal Vallis (∼28°S, ∼42°W), as imaged by Mariner 9. This large channel is ∼300   miles long; it borders the Coprates Quadrangle and the Margaritifer Quadrangle to the north of the Argyre impact crater. North is up. 

Image credit: NASA/JPL-CalTech.

3. Notes

BG references the Boston Globe, 29 November 1964–10 March 1973.

Introduction

Stephen M. Clifford,     Planetary Science Institute, Tucson, AZ, United States

Since the Mariner 4 provided the first close-up images of Mars in July of 1965, investigations by robotic spacecraft have provided substantial evidence that the atmosphere and surface of Mars have undergone a lengthy and complex evolution that continues to the present day (Soare et al., Prologue). This conclusion is supported by a variety of impact, volcanic, tectonic, fluvial, periglacial, and eolian landforms, many of which display a low density of superposed craters and are, therefore, thought to be geologically young (∼0–500  million  year, a period known as the Late Amazonian Epoch) (Hartmann, 2005; Tanaka et al., 2014; Williams, 2018; Chapter 12).

Current conditions of low atmospheric surface pressure (∼6  mb) and latitudinally variable mean annual surface temperatures (which range from ∼218K at the equator to ∼154K at the poles) preclude the year-round existence of liquid water at Mars’ surface. However, during the hemispheric spring and summer, daytime surface temperatures can exceed the melting point of water for up to several hours a day, perhaps even longer, given the presence of potent freezing point–depressing salts in the regolith (Clark and Van Hart, 1981; Hecht et al., 2009).

The duration of melting is influenced by quasiperiodic variations in the Martian climate, caused by changes in the Martian obliquity, orbital eccentricity, and precession. Of these, the obliquity of Mars (currently ∼25  degrees) exerts the greatest influence, varying with a period of ∼1.2  ×  10⁵  years with a maximum amplitude of as much as 10–15  degrees about the obliquity mean. The amplitude of this oscillation varies chaotically on a timescale ≥10⁷  years, producing extreme values of obliquity ranging from 0  degree to over 60  degrees (Laskar et al., 2004). These variations in obliquity, eccentricity, and precession influence the planet’s climate on timescales as short as ∼10⁴–10⁶  years—particularly with regard to the exchange of water between its atmospheric, surface, and subsurface reservoirs (Mischna, 2018; Chapter 1).

This record of climatic exchange is best preserved in the stratigraphy of water ice and dust visible in the north and south polar layered deposits (PLD); the latter are the planet’s principal H2O cold traps. The extensive layering within the several kilometers-thick and ∼1000–1500-km wide PLD, combined with estimates of their age (inferred from the number of superposed craters), suggests that the PLD preserve a stratigraphic record of climate change that ranges from ∼10⁷ to >10⁹  years, modulated by the variations in insolation caused by the quasiperiodic changes in the planet’s obliquity and orbital elements (Byrne, 2009; Mischna, 2018; Chapter 1; Portyankina and Aye, 2018; Chapter 6).

The seasonal changes in polar insolation, due to the planet’s current 25  degrees obliquity, are sufficient to generate winter temperatures cold enough for CO2 (which comprises ∼96% of the gas in the Martian atmosphere) to precipitate onto the surface. Consequently, as much as 30% of the atmosphere condenses at the winter pole; this produces a seasonal deposit of ice and frost, from several microns up to ∼1–2-m thick, which extends from ∼50 degrees latitude to the respective hemispheric pole. This seasonal condensation of atmospheric CO2 contributes to the growth of the PLD by the cold-trapping of H2O vapor (which is present in trace amounts in the atmosphere) and by enhancing the precipitation of both H2O ice crystals and atmospheric dust (raised by local and global dust storms), which act as condensation nuclei for atmospheric CO2.

In some areas of the seasonal cap the CO2 ice forms a transparent slab, ∼1-m thick, which allows the spring sunlight to penetrate and warm the subsurface—causing the sublimation of CO2 at the base of the ice and a build-up of gas pressure (Portyankina and Aye, 2018; Chapter 6). Eventually, the gas pressure becomes great enough to rupture the slab—creating patterns of spider-like radial channels, dendritic troughs, and furrows beneath the ice as the escaping gas erodes and fluidizes the underlying sand, dust, and CO2 and vents it to the surface (Portyankina and Aye, 2018; Chapter 6).

By late spring, the increased insolation causes the seasonal cap to sublimate, revealing the underlying PLD. In the north, the surface of the PLD is composed of water ice. However, in the south, much of the PLD is covered by a ∼8-m thick residual layer of CO2 ice that persists throughout the year (Portyankina and Aye, 2018; Chapter 6). An unusual landform associated with this residual CO2 ice consists of quasicircular flat-floored depressions (with diameters ranging from ∼0.1–1  km) that looks like swiss cheese. The size of these circular pits grows during the southern summer, the result of the preferential sublimation of CO2 ice from the pit walls caused by the increased insolation they experience (vs. the pit floor) due to the low sun angles at polar latitudes.

At low obliquity, both the north and south PLD act as net cold traps for H2O. However, at high obliquities, water ice is preferentially sublimed from the PLD and redistributed to lower latitudes, where it precipitates—along with atmospheric dust—and forms icy mantles and glacier-like landforms over the mid- and high-latitude terrain (Soderblom et al., 1973; Kreslavsky and Head, 2002). The extent and ice content of these latitude-dependent mantles have been confirmed by the observation of recent small (∼5–10-m wide) impact craters by the HiRISE camera on NASA’s Mars Reconnaissance Orbiter spacecraft (Dundas et al., 2014), which show that, shortly after an impact, the interior of the resulting crater exposes a bright white material that slowly disappears over the course of several months—consistent with the predicted sublimation of exposed ice at these latitudes.

The preservation state of these latitude-dependent mantles varies from location to location. Utopia Planitia (46.7°N, 117.5°E) is one area where the icy mantle has apparently undergone extensive sublimation, showing substantial fragmentation and ablation. Antecedently, it is thought that the current icy mantle (or perhaps an earlier one) underwent a climatically-modulated freeze-thaw cycling of water, enabling the underlying terrain to become ice rich (Soare et al., 2018; Chapter 7). On Earth, the ice enrichment of sediments is required to develop periglacial ice-complexes, i.e. permafrost populated by thermokarst, clastically sorted and unsorted polygons, etc. Sublimation, subsequently, could have de-volatilised the terrain, forming the alas-like depressions that are ubiquitous in the region (Soare et al., 2008).

Glacier-like landforms are found in Utopia Planitia and elsewhere throughout the mid-latitudes. The best-known examples are called lobate debris aprons, which are found principally around topographic knobs and at the base of scarps and have convex longitudinal profiles that suggest that they flowed outward over the Martian landscape (Squyres, 1979; Head et al., 2005). Two related landforms, which share the same latitudinal distribution and morphologic indications of flow, are lineated valley fill (where the confined flow of ice-rich material in narrow valleys has resulted in the formation of parallel longitudinal grooves and ridges) and concentric crater fill (where flow has occurred down the interior slopes of craters forming a concentric pattern of compressional cracks and ridges) (Squyres, 1979; Levy et al., 2010). Crater dating indicates that all of the latitude-dependent mantle landforms are young—the likely remnants of Late Amazonian Epoch ice ages associated with high obliquities.

Other potential examples of the deformation of ice-rich near-surface material on local slopes are small-scale lobate forms, which occur in both the northern and southern hemispheres at mid- to high-latitudes (Johnsson et al., 2018; Chapter 8). On Earth, the development of these landforms, by a process of periglacial mass-wasting known as solifluction, requires the presence of liquid water, which may occur on Mars when the ice-rich latitude-dependent mantle is warmed at times of high obliquity (Johnsson et al., 2018; Chapter 8). The association of ice with these lobate landforms is supported by their similar distribution and association with other periglacial landforms, such as small-scale polygons, whose origin may be due to thermal contraction cracking or repeated cycles of freeze–thaw (Soare et al., 2018; Chapter 7).

Gullies are another geologically recent (≤10⁷  years) landform whose distribution is associated with the latitudinal mantle (Conway et al., 2018; Chapter 3). They typically begin as alcoves, found near the top of steep slopes, from which a sinuous channel emerges that terminates in a downslope debris apron. Gullies are preferentially found on poleward-facing slopes in both hemispheres between the latitudes of ∼40–70  degrees—although gully orientations do vary, particularly at lower latitudes.

Initial observations seemed to suggest that gully flow was the result of a local discharge from a near-surface aquifer (Malin and Edgett, 2000). On the other hand, the presence of near-surface aquifers appears hydrologically and thermodynamically unlikely. More plausible origins include the melting of climatically deposited snowpacks during times of high obliquity, dry granular flow, and the fluidization of the regolith by subliming CO2 (Portyankina and Aye, 2018; Chapter 6). However, no single process appears to satisfy all of the observational constraints—suggesting a polygenetic origin (Conway et al., 2018; Chapter 3).

Although many of the Late Amazonian Epoch landforms related to water and ice are associated with the latitudinal mantle, other possible water-related features are found at low and equatorial latitudes. One recently discovered example of these are recurrent slope lineae (RSL)—narrow dark streaks that form on predominantly west- and equatorward-facing slopes, at low-to mid-latitudes, which appear to propagate downhill on a timescale of weeks to months during the hemispheric spring, and then fade away by the end of summer (McEwen et al., 2011; Stillman, 2018; Chapter 2). RSL occur on a variety of steep slopes—including canyon and crater walls, on the flanks of mesas, and on crater central peaks and pits. Their seasonal, latitudinal, and preferential slope-orientation initially suggested an association with transient flows of liquid water/brine. However, more recent studies indicate that RSL might also be explained by dry granular-flow processes involving the destabilization of eolian sediment on steep slopes by the thermally induced increase in CO2 pore gas pressure (Schmidt and Portyankina, 2018; Chapter 5).

Stillman (2018, Chapter 2) analyzed the characteristics of 748 candidate and confirmed RSL sites and concludes that no single formation mechanism can adequately explain all of the RSL observations. Discriminating between these different possibilities is likely to require a combination of enhanced remote sensing, more advanced modeling, or a larger set of in situ observations.

Whereas the involvement of liquid water in the formation of gullies and RSL is debated, persuasive evidence exists for the role of water in the formation of a number of Late Amazonian Epoch channels. Hargitai and Gulick (2018, Chapter 4) examined three groups of Late Amazonian Epoch fissure-fed channels that lie to the east–northeast of Olympus Mons. The morphology and superpositional relationships of the deposits within the channels suggest that they originated from multiple discharges of both lava and water from the fosse at their head—and have undergone additional modification by tectonism and collapse.

One of the more persuasive pieces of morphologic evidence supporting a fluvial formation hypothesis is the presence of streamlined forms within the channel interiors—features that typically are associated with fluvial processes on Earth. Streamlined islands are also found within the sinuous rilles that were carved by flowing lavas on the Moon, Venus, and Mercury—as confirmed by the vast lava-flow fields found at their termini (Leverington, 2004). However, there is little evidence of vast lava-flow fields at the termini of most Martian channels—suggesting that, like their terrestrial counterparts, they were carved by water.

In addition to the photogeologic and spectroscopic evidence that flows of liquid water and lava have sometimes occupied the same channels, there is widespread evidence of the interaction between water and volcanic processes elsewhere on Mars. For example, there are features that resemble terrestrial maars and cavi (Williams et al., 2018; Chapter 9). Maars are broad volcanoes with shallow, steep-sided craters at their centers. They form when ascending magma comes into contact with near-surface groundwater, causing the latter to flash into steam; this creates a massive explosion that pulverizes and ejects the overlying rock in an eruption of volcanic ash, steam, and magma. Morphologically, cavi are more subtle—consisting of depressions or pits that sometimes show evidence of internal lobate flows (Williams et al., 2018; Chapter 9). Cavi are believed to form when an ice-rich deposit is heated and melted from below by a magmatic intrusion. Examples of maar and cavi-like landforms are particularly evident in the Dorsa Argentea Formation; the latter is thought to be a relic of the south PLD that were more extensive in the Hesperian than they are today (Head and Wilson, 2007). However, Williams et al. (2018, Chapter 9) identify similar features in the northwestern part of the nearby Argyre impact basin, suggesting that it too contains ice-rich deposits. If these deposits were emplaced during one of the latest obliquity excursions, it argues for very recent local volcanic activity—perhaps the youngest on the planet.

Observations conducted from orbit by the Mars Express OMEGA and Mars Reconnaissance Orbiter CRISM infrared spectrometers have revealed the presence of evaporite mineral deposits in many areas across the planet (Bibring et al., 2006; Murchie et al., 2009). Such deposits are formed when readily soluble crustal minerals, such as gypsum and sulfate, are dissolved by rain or groundwater that pool on the surface and evaporates—leaving behind deposits of the dissolved minerals. Should these deposits be exposed to liquid water again (say, from the melting of surface ice deposits), then the resulting dissolution of the evaporites can create a complicated but identifiable landscape of broad depressions, sinkholes, towers, and caves. Baioni (2018, Chapter 14) discussed a possible evaporite landscape in western Noctis Labyrinthus (6.8°N, 261.1°E), at the western end of Valles Marineris; the landscape has no superposed craters (indicating a young age) and its formation is consistent with transient episodes of equatorial ice deposition and melting during the Late Amazonian Epoch.

Eolian processes are the most active of all the erosional and depositional processes on Mars. The evidence for eolian activity is pervasive and includes observations of local and global dust storms and extensive dune fields (Hayward et al., 2007; Bishop, 2018; Chapter 11). The geographic distribution and orientation of dune fields is an important marker of both past and present wind patterns and the nature of the climate that created them (Bishop, 2018; Chapter 11).

The amount of dust entrained in the atmosphere is important because: (1) it acts as nucleation centers for the formation of clouds (Kok et al., 2012); (2) it affects the climate by the reflection of incoming sunlight and the absorption of outgoing thermal radiation (Reiss, 2018; Chapter 10); and, (3) it contributes to the formation of the latitude-dependent mantle and other eolian deposits across the planet (Tanaka, 2000; Head et al., 2003; Bishop, 2018; Chapter 11). Atmospheric general circulation models indicate that roughly half of the dust load of the Martian atmosphere originates with dust devils (Kahre et al., 2006; Whelley and Greeley, 2006; Reiss, 2018; Chapter 10)—tornado-like convective vortices that are driven by solar radiation. As a result, most dust devils develop in the spring and summer of both hemispheres, when solar insolation is at a maximum.

The Martian regolith is the result of a variety of impact, erosional, and weathering processes that have resulted in a diverse mixture of particles, with a variety of shapes, ranging in size from clays to boulders. The erosion of the surface by wind or water can remove the smaller particles of sand and dust, leaving behind the larger rocks. Over time, this can create a stone pavement consisting of a thin layer of rocks that overly more fine-grained soil, where the development of the rock layer helps protect the local surface from further erosion (Dixon, 2015a,b, 2018; Chapter 13). In this respect, the resulting stone pavement represents a lag deposit—which is left behind when the action of wind or water has removed the original regolith matrix of dust and sand.

A similar process can occur in a volatile-rich unit composed of a mixture of ice and dust (such as the PLD). If such a unit is exposed to warmer conditions—as might occur at the poles at times of high obliquity—it can cause the ice to sublime away, leaving behind a lag deposit of the previously embedded dust. As the sublimation of ice continues, the lag deposit of dust grows thicker—providing both a layer of thermal insulation (which protects the underlying ice from diurnal temperature extremes, thus reducing the sublimation rate) and creating a diffusive barrier that physically inhibits the escape of subliming H2O molecules from the ice. Perhaps the best example of this is the 1500  km in diameter south-polar layered-deposits of which all but the central 350  km is covered by a lag deposit of Martian dust (Byrne, 2009). Lag deposits and stone pavements are ubiquitous on Mars and their formation is part of an ongoing process that has occurred throughout Martian geologic history and continues today (Dixon, 2018; Chapter 13).

Finally, impact processes have played a major role in the structural evolution of the Martian crust. Impacts modify the structure of a planetary surface in two important ways: by the production and dispersal of large quantities of ejecta and through the intense fracturing of the surrounding and underlying basement. Because the population of potential impactors (asteroids) crossing the orbit of Mars increases dramatically with decreasing size, the frequency of small impacts (craters ∼1–10  m diameter) is considerably greater than the frequency of large impacts (craters with diameters ≥100  km). Indeed, the high-resolution cameras onboard the Mars Global Surveyor and Mars Reconnaissance Orbiter have recorded many hundreds of small impacts over their mission lifetimes (McEwen et al., 2015). On the other hand, Mars has experienced only one impact as large as 13.8  km in diameter in the past 100  million  years (Williams, 2018; Chapter 12) and a handful of impacts resulting in craters >100  km in diameter over the past several billion years (Robbins et al., 2013).

Because the impact flux has been nearly constant over the past few billion years, the crater size frequency distribution (CSFD) of the surface can be used to date that surface’s age (Hartmann, 2005; Williams, 2018; Chapter 12). Thus, the longer a surface has been exposed to this constant impact flux, the greater the number of superposed craters per unit area. Likewise, the fewer craters present, the younger the terrain. This provides a relative way of dating Martian surfaces; absolute age estimates are based on a comparison between the Martian CSFD and that of the Moon, although the latter exhibits a cratering flux that is ∼3× greater than Mars (Williams, 2018; Chapter 12).

Large impacts produce sizable ejecta that reimpact the surface over considerable distances. These secondary craters often are difficult to distinguish from the primary impacts that occur in the same size range, creating a problem in the blind application of CSFDs to determine the absolute age of a surface (Hartmann, 2007; McEwen and Bierhaus, 2006). This, and other impact-related issues, are discussed by Williams (2018, Chapter 12).

This book is a collection of perspectives on the recent and current landscapes of Mars, as well as the processes that shaped them. The geologic evidence indicates that Mars remains a dynamic planet where the actions of water and ice, wind, volcanism, impacts, and climate continue to leave their mark on the planet’s surface. Our understanding of these processes and landforms is still evolving but will be made clearer by the continued acquisition and analysis of data from ongoing robotic exploration of Mars (Garvin, 2018; Epilogue).

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Section 1

Late Amazonian Epoch Climate

Outline

Chapter 1. Orbital (Climatic) Forcing and Its Imprint on the Global Landscape

Chapter 1

Orbital (Climatic) Forcing and Its Imprint on the Global Landscape

Michael A. Mischna     Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, USA

Abstract

In this chapter, we review the history of Mars climate observations and discuss our current understanding of how the martian climate evolves with time, focusing on recent Mars history covering the past several tens of millions of years. There is substantial observational and theoretical evidence to suggest that there have been dramatic, and regular, shifts in Mars' climate that would have periodically made the Mars of the past unrecognizable to modern day observers. Changes in the axial tilt, orbital eccentricity, and precession of Mars' perihelion work in concert to redistribute water across the surface, forming residual deposits which are readily observed, but which do not align with the present-day surface deposits of water ice, and which indicate a different climate equilibrium at times in the past. The climate forcing mechanisms that influence these deposits are addressed, and we discuss what this means for establishing a timeline of Mars' recent climate history. We subsequently address the means by which volatiles are emplaced on, and within, the surface, distinguishing between diffusive processes that migrate water vapor into and out of the subsurface, and those depositional processes that emplace water ice directly on the surface as snowfall. We further consider the role of periglacial activity and putative liquid water availability on the vertical migration of water in the subsurface. Lastly, we review various ways in which water provides visual, textural, and morphological evidence for recent climate change. We illustrate several examples of observed features that establish the distribution of water ice throughout recent Mars history, the climates required for its emplacement, and the residuals of its subsequent removal. By following this relict evidence of martian water ice, we can begin to weave a story of Mars' recent past—one that shows the breadth of climate states over time, of which the present day is but one example.

Keywords

Atmosphere; Climate; Eccentricity; Glacial; Ice; Obliquity; Periglacial; Water

Chapter Outline

1.1 Introduction

1.1.1 A Brief History of Mars Climate Observations

1.1.2 The Present Atmosphere of Mars

1.2 Climate Forcing

1.2.1 Obliquity

1.2.2 Eccentricity

1.2.3 Argument of Perihelion

1.2.4 Total Insolation

1.2.5 Orbital-Driven Circulation

1.2.6 Surface Properties

1.2.7 Putting It Together

1.3 Volatile Emplacement

1.3.1 Surface Layering

1.3.2 Atmospheric Dust

1.3.3 Subsurface Ice and Vapor Diffusion

1.3.4 Liquid Water

1.4 Morphological Evidence for Recent Climate Change

1.4.1 Polar Ice

1.4.2 High-Latitude Ice

1.4.2.1 Observations by Mars Odyssey Gamma Ray Spectrometer

1.4.2.2 Measurements by the Mars Phoenix Lander

1.4.3 Mid-Latitude Ice

1.4.3.1 Latitude-Dependent Mantle

1.4.3.2 Pedestal Craters

1.4.3.3 Other Impact Craters

1.4.3.4 Expanded Impact Craters

1.4.3.5 Scalloped Depressions

1.4.3.6 Putative Periglacial Landforms

1.4.3.7 Terraced Craters

1.4.4 Other Mid- and Low-Latitude Ice Deposits

1.4.4.1 Pasted-on Terrain and Gullies

1.4.4.2 Lobate Debris Aprons, Lineated Valley Fill, and Ice-Rich Flows

1.4.4.3 Radar Observations

1.4.4.4 Tropical Mountain Glaciers

1.5 Conclusions

Acknowledgments

References

1.1. Introduction

1.1.1. A Brief History of Mars Climate Observations

Mars climate science has been an active field of study since the earliest days of planetary exploration, preceding even humankind’s first robotic exploration of the Red Planet in the 1960s. Of the keenest interest has been the question of the availability of water at the martian surface. Water is a required element for life as we know it, and its presence on Mars opens the door to many tantalizing ideas about the existence of life on our celestial neighbor. As presented in this book’s introduction (Prologue: Mariner’s Way: Beyond the Future to the Past), the first scientific results from Mariner 4 and subsequent findings from her sister Mariner spacecraft truly rewrote the book on questions of Mars’ habitability and its surface environment, at once turning a hypothesized verdant and inhabited planet into a dry and deserted Moon-like wilderness. This transition, however, was just the first of several marked shifts in how we have perceived the climate and environment of Mars over the past 60+  years.

Following these groundbreaking studies of the Mariner spacecraft, it was the two Viking Landers and Orbiters of the late 1970’s and early 1980s, with their multiyear life span and dedicated instrumentation, which revealed a strikingly more complex water cycle than previously anticipated from analysis of Mariner data—one involving year-round polar caps, seasonal frost deposits, and an atmosphere actively shuttling water across the planet over the course of the year (Fig. 1.1). Highly detailed images of complex valley networks and outflow channels and the ability to age-date these features to different historical epochs forced reconsideration of the then-dismissed idea that Mars supported recent surface activity, including flowing water, precipitation, and perhaps transient bodies of liquid water. The Mars Atmospheric Water Detector (MAWD) on the Viking Orbiters found trace amounts of water in the atmosphere (on the order of 10’s of pr-μm¹) and a highly repetitive annual cycle of atmospheric water vapor transport. Mars had now gone from having what was presumed to be a static evolutionary history to one apparently evolving with time, and which continues to evolve up to the present day. This was yet another major paradigm shift in our interpretation of the martian environment.

A two-pronged legacy of the Viking missions persists to the present day. First, Viking established that the climate history of Mars was not stagnant, but rather constantly evolving and, second, it abolished the notion that Mars was a dry, Moonlike world. Though not as green as once envisioned, it was nevertheless a significantly more dynamic environment than once anticipated.

Figure 1.1  Mars Atmospheric Water Detector (MAWD) column water vapor for two martian years. Note that the water vapor maximum occurs in northern summer. Blue bars in the left panel indicate period of the 1977a and 1977b global dust storms. See Section 1.2.3 for definition of areocentric longitude of the Sun (L s ). 

Copyright 2002 Wiley. Used with permission from Richardson, M.I., Wilson, R.J., 2002a. Investigation of the nature and stability of the martian seasonal water cycle with a general circulation model. J. Geophys. Res. 107 (E5), 5031, Wiley; data from Farmer, C.B., Davies, D.W., Holland, A.L., Laporte, D.D., Doms, P.E., 1977. Mars—water vapor observations from the Viking Orbiters. J. Geophys. Res. 82, 4225–4248; Jakosky, B.M., Farmer, C.B., 1982. The seasonal and global behavior of water vapor in the Mars atmosphere—complete global results of the Viking atmospheric water detector experiment. J. Geophys. Res. 98, 2999–3019.

Following the achievements of Viking, it was nearly 20  years before the next successful long-term encounters with Mars. A flotilla of orbiting spacecraft has now studied Mars continuously since the late 1990s—including the Mars Global Surveyor in 1997, Mars Odyssey in 2001, Mars Express in 2003, the Mars Reconnaissance Orbiter in 2005, MAVEN and the Indian Mars Orbiter Mission in 2013 and, most recently, the ExoMars Trace Gas Orbiter in 2016. These orbiting spacecraft have yielded, and will undoubtedly continue to yield, a wealth of new data about Mars, including information about its present climate and surface environment, and observations of ongoing surface change, including the possible effects of liquid water. Further discoveries by stationary and mobile spacecraft, including Mars Pathfinder, the twin Mars Exploration Rovers Spirit and Opportunity, in 2004, Phoenix in 2007, and the Mars Science Laboratory Curiosity in 2011 have confirmed that liquid water on the martian surface was widespread in the past and that conditions may yet still be conducive to liquid even at the present.

What we have seen from the growing archive of post-Viking observations is that the evolution of Mars’ climate has not been a secular process. In addition to large-scale shifts in climate over billions of years (for example, the evolution from what was almost certainly a warmer, wetter early climate to the present-day dry conditions), there is evidence for more intermediate-scale shifts of hundreds of thousands to tens of millions of years, and even small-scale shifts on decadal to millennial timescales. The observable and quantifiable consequences of these changes are well-documented across the planet. The presence of seemingly out-of-equilibrium water deposits in the martian tropics, different geomorphological and geochemical signatures, and a host of theoretical and numerical arguments are the key to dissecting Mars’ recent² climate. These, and other signatures of recent climate change on Mars, are the subject of this chapter.

1.1.2. The Present Atmosphere of Mars

Let us pause a moment to quantify the present state of the martian atmosphere and climate, from which we may then draw comparisons to past martian environments. Presently, the atmosphere has a surface pressure that falls in the range of ∼3–12  mb—about 1% that of Earth, and which comprises 95.97% carbon dioxide, 1.93% argon, and 1.89% nitrogen, with the remaining ∼1% consisting of various trace species, the most important of which is water vapor (Mahaffy et al., 2013). Surface temperatures on Mars are sufficiently cold (with a mean annual temperature of ∼200K) so as to seasonally reach the frost point temperature of CO2 (∼148K) at both poles during winter, resulting in the condensation of up to 25% of the total mass of the atmosphere during the solstice seasons (Fig. 1.2). At the cold martian temperatures, only traces of water vapor are found in the atmosphere—the mean global water vapor content is only ∼10–20  pr-μm—and liquid water is not generally stable at the surface.

The poles of Mars are covered by permanent water ice caps, much like Earth. In the south, the polar cap is covered by a permanent, thin veneer of CO2 ice of unknown provenance. Every winter season, the condensing atmosphere forms thicker seasonal CO2 ice deposits over the winter pole during the long polar night. The permanent water ice caps play a key role in regulating the martian water cycle and, hence, the present climate, and will serve as the cornerstone for our present discussion of recent climate change. Nearly all of the evidence of such change stem from variations and variability in Mars’ water ice deposits, as we shall see.

A small fraction of Mars’ water budget is found in atmospheric clouds, which are most prevalent in two distinct reservoirs. During the cooler northern summer season, which occurs at aphelion, when Mars is furthest from the Sun, clouds form along a band straddling the equator, referred to as the aphelion cloud belt. Thicker and more expansive water ice clouds, known as the polar hood, form over the polar caps during the winter season. We shall return to a discussion of water ice clouds in a later section.

Additionally, we shall explore the importance of atmospheric dust on the changing climate, and so a few words about the present role of dust are warranted here. Dust has a significant influence on the present martian atmosphere. With respect to the annual cycle of atmospheric dust, the martian year can be loosely divided into two halves, the clear season and dust storm season, which encompass the northern spring/summer and southern spring/summer, respectively. During the clear season, when Mars is more distant from the Sun, atmospheric circulation is relatively muted, dust is found in smaller quantities in the atmosphere, and it has only a slight influence on atmospheric heating. Dust storm activity is generally limited to the smallest storms, which can be numerous, but which are transient and local in nature. During the dust storm season, however, when Mars is closer to the Sun, dust is much more widespread in the atmosphere. Its presence is prompted by more energetic atmospheric circulation and enhanced surface lifting in the dust storm season (which roughly centers around perihelion), and it strongly affects the thermal balance of the planet by stirring up both local (10–100  km) and regional scale (100s–1000s  km) dust storms. On occasion during the dust storm season, planet-encircling global dust storms form, which enshroud the entire planet in a thick, dusty haze, obscuring the surface from view. The Mariner 9 orbiter encountered Mars during the height of one of these storms and the Viking Landers and MER rovers witnessed similar storms from the martian surface. This clear/dusty cycle is highly repetitive, year over year, although the development of global dust storms occurs only infrequently and irregularly.

Figure 1.2  The annual pressure cycle at Mars, as measured by Viking Lander 1 (green colors), Viking Lander 2 (gray colors), Mars Pathfinder (black), Mars Phoenix Lander (purple), and Mars Science Laboratory (red/orange colors). The offset between the curves is real and reflects the different elevations of the spacecraft. The jump in surface pressure seen by Viking 2 around northern winter solstice in MY 12 is a consequence of a global dust storm, which erupted during the Viking Lander missions. The MY nomenclature refers to a Mars year, as defined in Clancy et al. (2000) . 

From Martínez, G.M., et al., 2017. The modern near-surface martian climate: A review of in-situ meteorological data from Viking to Curiosity. Space Sci. Rev. 212, 295–338. The figure is modified from the original source, and is provided under the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/).

1.2. Climate Forcing

What ultimately regulates the climate on Mars is, like all celestial bodies, the distribution of insolation at the surface. The distribution of insolation on any planet