From Habitability to Life on Mars

Nathalie A. Cabrol, Edmond A. Grin

• Publisher: Elsevier
• Year: 2018
• Print ISBN:
  9780128099353
• eBook ISBN:
  9780128099360
• Topic: Physical Sciences
• Subtopic: Geophysics

From Habitability to Life on Mars explores the current state of knowledge and questions on the past habitability of Mars and the role that rapid environmental changes may have played in the ability of prebiotic chemistry to transition to life. It investigates the role that such changes may have played in the preservation of biosignatures in the geological record and what this means for exploration strategies. Throughout the book, the authors show how the investigation of terrestrial analogs to early Martian habitats under various climates and environmental extremes provide critical clues to understand where, what and how to search for biosignatures on Mars. The authors present an introduction to the newest developments and state-of-the-art remote and in situ detection strategies and technologies that are being currently developed to support the upcoming ExoMars and Mars 2020 missions. They show how the current orbital and ground exploration is guiding the selection for future landing sites. Finally, the book concludes by discussing the critical question of the implications and ethics of finding life on Mars. - Edited by the lead on a NASA project that searches for habitability and life on Mars leading to the Mars 2020 mission - Presents the evidence, questions and answers we have today (including a summary of the current state of knowledge in advance of the ESA ExoMars and NASA Mars 2020 missions) - Includes contributions from authors directly involved in past, current and upcoming Mars missions - Provides key information as to how Mars rovers, such as ExoMars and Mars 2020, will address the search for life on Mars with their instrumentation

Color Plate 1

Plate 1 From habitability to life? Forty years of exploration has provided converging evidence that early Mars was habitable for life as we know it. Whether life ever took hold is a question that will be addressed by the next generation of missions, starting with Mars 2020 and ExoMars. Credit image: NASA/JPL-Caltech/MSSS. Dingo Gap captured by the Curiosity rover at Gale crater, Mars.

Color Plate 2

Plate 2 Elements of Martian habitability. Top left—Mastcam image of a section of the Murray Buttes at Gale crater captured by the Curiosity rover on 8 September 2016. The buttes and mesas are eroded remnants of ancient sandstones. Credits: NASA/JPL-Caltech/MSSS. Top right—Lava deposits and sequences of sedimentary layered deposits in the background captured in the foothill of Mount Sharp, Gale crater, Mars. Credits: NASA/JPL-Caltech/MSSS. Middle panel—The Comanche outcrop holds key mineralogical evidence for an ancient lake in Gusev crater. Image by NASA/JPL-Caltech/Cornell University: Mars Exploration Rover mission and Spirit rover. Bottom left—Opaline silica deposits in a series of depressions in Noctis Labyrinthus as viewed from orbit by HiRISE onboard MRO. The opal could have formed by chemical weathering of basaltic lava flows or ash in the presence water. Credit image: NASA/JPL/University of Arizona. Image ID: ESP_023359_1710. Bottom right—Mastcam image showing a pattern typical of a lake-floor sedimentary deposit not far from where flowing water entered a lake. Credits: NASA/JPL-Caltech/MSSS: NASA's Curiosity Mars rover.

Chapter 1

Habitability as a Tool in Astrobiological Exploration

Jack D. Farmer

Abstract

While “follow the water” has been an extraordinarily effective strategy in the search for habitable environments in the solar system, astrobiologists will require a more refined approach to exploration during the next phase of exploration when we will begin to target specific habitable sites for deploying a new generation of in situ life detection experiments. Identifying the best sites for in situ experiments or for selecting samples for return to Earth will likely require a more refined knowledge of past and/or present aqueous environments, with an ability to detect HZs at the microscale. Success in detecting extraterrestrial life may require a spatially integrated sampling strategy that includes the ability to measure multiple microenvironmental factors at each study site. Such microscale, multidimensional approaches have been employed in the past by microbial ecologists to refine and quantify biological concepts like the niche. Such approaches may prove useful in more effectively conveying the concept of habitability.

Keywords

Habitability; Astrobiology; Extremophiles; Solar system exploration

Contents

• 1.1 Overview
• 1.2 Introduction
• 1.3 Defining Habitability
  • 1.3.1 Follow the Water
  • 1.3.2 Follow the Bioessential Elements
  • 1.3.3 Follow the Energy Sources
• 1.4 Exploring the Extremes of Life
• 1.5 Niche-Based Multivariate Approach to Habitability
• 1.6 Conclusions
• References
• Further Reading

1.1 Overview

The exploration strategy currently guiding the search for life in the solar system begins with a short list of the fundamental resources required by terrestrial life. The most important of these requirements is liquid water. Second in importance are sources of biologically essential elements, the so-called CHNOPS elements (required for all living systems), plus a dozen or so transition metals that fulfill important roles in coenzyme functions in cells. Third, life requires sources of energy, obtained through chemical redox reactions. This simple, three-pronged strategy is usually embodied in the phrase “follow the water.” This approach to habitability has served astrobiology well, with recent missions reporting evidence for past and present water on Mars and in the subsurface of tidally heated icy moons (e.g., Enceladus and Europa). While the “follow the water” strategy has proved successful in discovering potentially habitable zones (HZs) of liquid water in these and potentially other extraterrestrial environments, understanding the potential for life to actually develop and persist in these places remains unclear. On Earth, habitability depends on the coexistence of three things: liquid water, energy sources and chemical building blocks. However, it is also clear that, on Earth, life exists within a complex web of ecological interactions that, through evolution, have continually reshaped the origin, nature, and distribution of species. Stated differently, life on Earth is a powerful ecological force that itself shapes habitability.

As a testimonial to the power of eco-evolutionary forces to shape the history of the biosphere, discoveries of extremophiles have revealed that terrestrial life occupies a much broader range of environmental extremes than once thought possible. On planetary surfaces, organisms have evolved metabolic strategies that extract energy from sunlight, over an impressive range of environmental conditions (e.g., temperature, pH, and water activity). Particularly impactful, however, are life forms that do not require sunlight but rather subsist on chemical energy from their surrounding environment. These “chemotrophic” microorganisms are part of an extensive subsurface biosphere that resides in deep subsurface habitats on the Earth. Of particular interest for astrobiological exploration are “chemolithoautotrophic” microorganisms that obtain energy from the chemical by-products of aqueous weathering of mafic crustal rocks. These microbes require no connection to the surface and can exist unseen from surface exploration.

Wh...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• List of Contributors
• Foreword
• Color Plate 1
• Color Plate 2
• Chapter 1: Habitability as a Tool in Astrobiological Exploration
• Chapter 2: An Origin of Life on Mars?
• Chapter 3: Remote Detection of Phyllosilicates on Mars and Implications for Climate and Habitability
• Chapter 4: Martian Habitability as Inferred From Landed Mission Observations
• Chapter 5: Archean Lakes as Analogues for Habitable Martian Paleoenvironments
• Chapter 6: Evolution of Altiplanic Lakes at the Pleistocene/Holocene Transition: A Window Into Early Mars Declining Habitability, Changing Habitats, and Biosignatures
• Chapter 7: Siliceous Hot Spring Deposits: Why They Remain Key Astrobiological Targets
• Chapter 8: Habitability and Biomarker Preservation in the Martian Near-Surface Radiation Environment
• Chapter 9: UV and Life Adaptation Potential on Early Mars: Lessons From Extreme Terrestrial Analogs
• Chapter 10: Are Recurring Slope Lineae Habitable?
• Chapter 11: The NASA Mars 2020 Rover Mission and the Search for Extraterrestrial Life
• Chapter 12: Searching for Traces of Life With the ExoMars Rover
• Chapter 13: Concluding Remarks: Bridging Strategic Knowledge Gaps in the Search for Biosignatures on Mars—A Blueprint
• Index