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2921 results in Planetary systems and astrobiology

Page 91 of 147

Planets and Life
  • The Emerging Science of Astrobiology
  • Edited by Woodruff T. Sullivan, III, John Baross
  • Published online:
    28 May 2018
    Print publication:
    13 September 2007
  • Astrobiology involves the study of the origin and history of life on Earth, planets and moons where life may have arisen, and the search for extraterrestrial life. It combines the sciences of biology, chemistry, palaeontology, geology, planetary physics and astronomy. This textbook brings together world experts in each of these disciplines to provide the most comprehensive coverage of the field currently available. Topics cover the origin and evolution of life on Earth, the geological, physical and chemical conditions in which life might arise and the detection of extraterrestrial life on other planets and moons. The book also covers the history of our ideas on extraterrestrial life and the origin of life, as well as the ethical, philosophical and educational issues raised by astrobiology. Written to be accessible to students from diverse backgrounds, this text will be welcomed by advanced undergraduates and graduates who are taking astrobiology courses.

  • Appendix C - The geological timescale

  • from PART VIII - Appendices
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 566-568

  • Summary

    The geological timescale is one of science's great triumphs. It represents “deep time” (McPhee, 1982), millions and billions of years ago, time beyond human comprehension. Geologists use two different ways to discuss geological time: (a) absolute time, and (b) relative time.

    Relative time was developed first, and is based on relative age relationships among rock units as determined by geometric relationships, fossils, and other distinctive attributes of the rock. Layered, sedimentary rocks (strata) are the most widely used, and during the nineteenth century allowed geologists to establish a relative geological timescale. The scale used strata with their contained fossils, and applied four fundamental principles of relative time: (1) original horizontality, (2) superposition, (3) original lateral continuity, and (4) fossil succession. Fossil succession refers to the particular vertical (stacked) order that fossils occur in strata. William Smith recognized this in 1799 and employed it to great effect in his geological map of England and Wales published in 1815. The other three principles were established much earlier by the Danish scholar Nicolaus Steno (1669). Original horizontality states that sediments are originally laid down in a horizontal or nearly horizontal manner. Superposition means that the oldest stratum is at the bottom and the youngest at the top. Original lateral continuity refers to the way strata extend laterally in all directions. The geometric relationship of bodies of rock to one another is also used; for example, an intrusion that cuts layered rock is younger than the layered rock it cuts.

  • Preface

  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp xix-xxii

  • Summary

    The emerging field of astrobiology encompasses a daunting variety of specialties, from astronomy to microbiology, from biochemistry to geology, from planetary sciences to phylogenetics. This is both exciting and frustrating – exciting because the potential astrobiologist is continually exposed to entirely new ways to look at the world, and frustrating because it is difficult to understand new results when venturing outside the confines of one's own specialty. There are now many excellent popular books on astrobiology, but a scientist wants more details and more sophistication than these afford. Where can an astronomer without any formal biology since high school learn the basics of cellular metabolism? Or the principles of evolution? Or notions about alternative forms of life? And where can a microbiologist with little physics and no astronomy learn the basics of how a planetary atmosphere works? Or how the Earth formed? Or how planets are detected around other stars? This book is designed to fill these needs.

    We have endeavored to cover all the important aspects of astrobiology at an advanced level, yet such that most of the contents in every chapter should be understandable to anyone versed in any relevant science discipline. We envision our youngest readers to be science majors near the end of undergraduate study or the beginning of graduate study. And at the other extreme, we aim to serve scientists who haven't taken an academic course for forty years, but are intrigued by the nascent field of astrobiology.

  • 10 - Evolution: a defining feature of life

  • from PART IV - Life on Earth
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 213-221

  • Summary

    In biology nothing makes sense except in the light of evolution. It is possible to describe living beings without asking questions about their origins. [But] the descriptions acquire meaning and coherence only when viewed in the perspective of evolutionary development.

    Theodosius Dobzhansky (1970: 6)

    From Lamarck to Darwin to the central dogma

    The basic notion of evolution is that inherited changes in populations of organisms result in expressed differences over time – these differences are at the gene level (the genotype) and/or expression of the gene into an identifiable characteristic (the phenotype). The important underlying fact of evolution is that all organisms share a common inheritance, or, put more dramatically, all extant organisms on Earth evolved from a common ancestor. We see this in the universal nature of the genetic code and in the unity of biochemistry: (a) all organisms share the same biochemical tools to translate the universal information code from genes to proteins, (b) all proteins are composed of the same twenty essential amino acids, and (c) all organisms derive energy for metabolic, catalytic, and biosynthetic processes from the same high-energy organic compounds such as adenosine triphosphate (ATP).

    In On the Origin of Species Charles Darwin (1859) (Fig. 10.1) built his theory of evolution using evidence that included an ancient Earth thought at the time by many geologists to have an age in millions of years. He also took the extinction of species to be a real phenomenon since fossils existed that were without living representatives.

  • Prologue

  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 1-6

  • Summary

    A new synthesis: the Biological Universe

    A remarkable shift in our scientific world picture is taking place, potentially as fundamental in its consequences as the new views put forth by Copernicus in the sixteenth century, or by Darwin in the nineteenth. Although astronomers have long been involved with the prospects for extraterrestrial life, their fundamental task since Newton has been to apply physics to a lifeless Universe. On the other hand, biologists have pursued their studies for centuries in cosmic isolation, meaning that biology considered life on Earth, with no attention paid to its cosmic context. Today, however, both camps are recognizing fruitful and exciting avenues of research created by a new synthesis. Biology is vastly enriched when attention is paid to a broader context for life as we know it, as well as the possibilities for other origins of life. And astronomy is coming to realize that the themes of cosmic, galactic, stellar, and planetary evolution, which have become central over the past century, must now also incorporate biological origin(s) and evolution(s). Historian of science Steven Dick (1996) has hailed this new synthesis as the Biological Universe. Although astronomy and biology are its two primary poles, many other disciplines are also vital components, in particular Earth and planetary sciences.

  • 15 - Life in ice

  • from PART IV - Life on Earth
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 292-312

  • Summary

    White men think of ice as frozen water, but Inuit think of water as melted ice. To us, ice is the natural state.

    Nuka Pinguaq, nineteenth-century native Arctic hunter (Kobalenko, 2002)

    Introduction

    Ice is the “natural state” or predominant form of water in our Solar System. The surfaces of most planets and moons are currently at temperatures well below the freezing point of pure water, including two of the more promising sites in the search for traces of extraterrestrial life, Mars and Europa. The amount of water-ice on Europa exceeds the volume of liquid water on Earth. Comets, considered potential vectors for precursors or early stages of life, are also icy bodies (Chapter 3). Even Earth may have undergone a series of complete (or near-complete) glaciations in its recent history, earning the title “Snowball Earth” (Section 4.2.4).

    The presence of the liquid phase of water, however, is essential to the prospering of life as we know it. In order to study where liquid water can occur, we must understand scales ranging from the structure of the water molecule to the temperatures possible on a planetary surface or subsurface. In our Solar System, only Earth allows for a planetary surface with abundant liquid water (Chapter 4). Mars, however, may well have some liquid water in permafrost (perennially frozen soil) beneath its surface today (Section 18.4.1), and the evidence is strong that Europa and perhaps other moons of Jupiter have water oceans below their icy crusts (Chapter 19).

  • 1 - History of astrobiological ideas

  • from PART I - History
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 9-45

  • Summary

    Overview

    Why history?

    The core questions of astrobiology are not new. They have always been asked and are central to Western intellectual history. How did life begin? How has it changed? What is the relation of humans to other species? Does life exist elsewhere? If so, where might it be and what is it like? Although these questions are ancient, what is new are the tools at hand to search for answers, ranging from robotic spacecraft to genome sequencing, from electron microscopes to radio telescopes. These tools and other factors (see the Prologue and Chapter 2) appear to have brought astrobiology to a point where it is gelling into something qualitatively different – our first sound attack on these questions. But is this so? Or is today no different from any other time in the past few centuries?

    In every era, including our own, scientists can do no more than tackle questions with the best tools available, apply the best insight they can muster, and struggle to fashion a consensus as to the nature of the world. In this manner our understanding has progressed, for example, from the “animalcules” that van Leeuwenhoek described three hundred years ago to the richness of contemporary microbiology. To understand such a thread as it meanders through history, we need to document more than the accumulation of facts. When evaluating a given episode, historians of science look carefully at evidence of not only the science itself, but also of the larger enveloping context.

  • 19 - Europa

  • from PART V - Potentially habitable worlds
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 388-423

  • Summary

    Introduction

    Europa, one of the four large satellites of Jupiter, is nearly the size of Earth's Moon. Tidal flexing driven by Jupiter's gravity and sustained by an orbital resonance with two other jovian satellites, Io and Ganymede, results in significant heat dissipation within Europa. Calculations indicate that this tidal heating is sufficient to maintain liquid water beneath Europa's ice crust. Moreover, observational evidence suggests that it is indeed probable, but not yet completely certain, that Europa harbors a subsurface ocean of liquid water whose volume is about twice that of Earth's oceans. The likely presence of abundant liquid water places Europa among the highest priority targets for astrobiology.

    To support life, Europa would also require an inventory of biogenic elements and a source of sufficient free energy. The ability to support life does not of course guarantee that the origin of life took place on Europa, or that life is present today; answering these questions will require further exploration. This chapter considers Europa in an astrobiological context, distinguishing among what is known, what is supported by evidence but still uncertain, and what remains more speculative. We conclude with a discussion of future missions that will be needed to address current geological and astrobiological questions.

    Jupiter and its satellites

    The planet Jupiter, orbiting the Sun at 5.2 AU, is more massive than the other planets in the Solar System combined; it is 3.3 times more massive than Saturn and 318 times more than the Earth.

  • 22 - How to search for life on other worlds

  • from PART VI - Searching for extraterrestrial life
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 461-472

  • Summary

    Introduction and summary

    In the original Star Trek series, Episode 26 (“The Devil in the Dark”), Mr. Spock uses a hand-held tricoder to remotely detect a silicon-based lifeform known as a “Horta.” Unfortunately, NASA engineers have not yet invented the tricoder to aid in our own search for life on Mars or Europa. In fact they are not even close to understanding the principle by which a tricoder is able to distinguish lifeforms, either carbon or silicon, from non-living matter. Even The Physics of Star Trek (Krauss, 1995) is notably silent on the operating physics behind the tricoder. How then do we achieve the Prime Mission of Astrobiology: to boldly go and seek out new lifeforms on distant worlds? The answer, not surprisingly, is that we base our search for life elsewhere on what we know about life on Earth. The basic elements of this approach can be summarized as follows.

  • There is no specific definition of life that usefully contributes to the search for life (see Chapter 5). Don't wait for one.

  • In searching for either extant or extinct life the most useful guide is the short list of the ecological requirements for life. These are: (a) energy, (b) carbon, (c) liquid water, and (d) other elements such as N, P, and S. On the planets of our Solar System liquid water is the limiting factor.

  • Life is composed of, and produces, organic (carbon-based) matter. Forget silicon-based life for now.

  • Organic matter of biological origin can be differentiated from other organic matter because life preferentially selects and uses a few specific organic molecules. This selectivity is probably a general feature of life.

  • […]

  • 17 - Mass extinctions

  • from PART IV - Life on Earth
  • Edited by Woodruff T. Sullivan, III, University of Washington, John Baross, University of Washington
  • Book:
    Planets and Life
    Published online:
    28 May 2018
    Print publication:
    13 September 2007, pp 335-354

  • Summary

    Introduction

    The frequency of animal life in the Universe must be some function of how often it arises, and then how long it survives after evolving. Both of these factors may be significantly influenced by the frequency and intensity of mass extinctions, brief intervals of time when significant proportions of a planet's biota are killed off. They are killed by one or some combination of too much heat or cold, not enough food or nutrients, too little (or too much) water, oxygen, or carbon dioxide, excess radiation, incorrect acidity in the environment, or environmental toxins. Based on the history of Earth's life, mass extinctions seemingly have the potential to end life on any planet where it has arisen.

    Mass extinctions do more than threaten biota. They may also play a large part in evolutionary novelty. On Earth there have been about 15 such episodes during the last 500 Myr, five of which eliminated more than half of all species then inhabiting our planet. These events significantly affected the evolutionary history of Earth's biota: for example, if the dinosaurs had not been suddenly killed off following a comet collision with the Earth 65 Ma, there probably would not have been an Age of Mammals, since mammals were held in evolutionary check so long as dinosaurs existed. The wholesale evolution of mammalian diversity took place only after the dinosaurs were swept from the scene. Mass extinctions are thus both instigators as well as foils to evolution and innovation.

  • 18 - Volcanism on Io: a post-Galileo view

  • Ashley Gerard Davies
  • Book:
    Volcanism on Io
    Published online:
    05 October 2014
    Print publication:
    09 August 2007, pp 287-293

  • Summary

    By the end of the Galileo mission, many characteristics of Io's volcanism had been identified for the first time. Processes were observed that continue to yield insight into the way volcanic activity helped shape the Earth and other terrestrial planets. This chapter summarizes the post-Galileo view of Io.

    Volcanism and crustal structure

    Galileo revealed a world dominated by silicate volcanism, putting to rest a major point of contention that dated back to Voyager. Galileo discovered many active volcanic centers on Io (Appendix 1), considerably more than were detected by Voyager. The global distribution of activity and volcanic features favors the heating of Io by tidal dissipation taking place, in large part, in the aesthenosphere – the partially molten upper mantle.

    The upper few kilometers of Io's crust appear to be mostly mafic silicates interbedded with deposits of sulphur, sulphur dioxide, and silicate pyroclasts. The thickness of this volatile-rich layer probably varies from location to location but provides plenty of material that is easily mobilized by thermal interaction with mafic magma. Ultramafic magmas may be present, but the wide error bars ascribed to the data do not show this conclusively. If recent data analyses (Keszthelyi et al., 2004a, 2005a) are confirmed, ultramafic volcanism may not be present or widespread, and the presence of a global magma ocean (e.g., Keszthelyi et al., 1999) may not be required.

  • 2 - Between Voyager and Galileo: 1979–1995

  • Ashley Gerard Davies
  • Book:
    Volcanism on Io
    Published online:
    05 October 2014
    Print publication:
    09 August 2007, pp 27-38

  • Summary

    After the Voyager encounters, analysis of the data continued. More hot spots were identified in IRIS data (see McEwen et al., 1996; also see Appendix 1). Early post-Voyager models of Io incorporated a sulphur-rich crust with an ocean of sulphur beneath (e.g., Sagan, 1979; Smith et al., 1979b, 1979c). The sulphur was kept liquid and mobile through interaction with hot or molten silicates within the crust (e.g., Lunine and Stevenson, 1985). This model was supported by the abundance of sulphur compounds on Io's surface and sulphur in the Io plasma torus and neutral clouds, and by the fact that silicates had not been detected on the surface. The occasional eruption of silicate lava was still possible, but Io's volcanism was dominated by sulphur lavas.

    Silicate volcanism on Io?

    The case for ubiquitous silicate activity was made by Carr (1986), who argued on the basis of crustal strength that the “sulphur ocean” postulated to lie close to the surface was unlikely, based on the strength of the crust needed to support the steep walls of many paterae, where temperatures in excess of 650 K would literally melt the caldera walls. Heat transport from Io's interior to the surface was via silicate volcanism. To support the observed mountains, Io required a predominantly silicate lithosphere at least as thick as the mountains were high (>15 km in some cases).

Page 91 of 147