Comets and the Origin of Life
The idea that comets may be connected with the origin of life on Earth was considered heresy a few decades ago, with scientists shying away from this possibility as if from a medieval superstition. However the case that comets may have contributed at least the complex organic building blocks of life has become very strong, and mechanisms have now been identified whereby comets may incubate and transfer microbial life from one cosmic habitat to another in the Galaxy. The latter process...
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The idea that comets may be connected with the origin of life on Earth was considered heresy a few decades ago, with scientists shying away from this possibility as if from a medieval superstition. However the case that comets may have contributed at least the complex organic building blocks of life has become very strong, and mechanisms have now been identified whereby comets may incubate and transfer microbial life from one cosmic habitat to another in the Galaxy. The latter process cometary panspermia was pioneered by the late Sir Fred Hoyle and one of the present authors in the early 1980's. A theory that was once controversial is slowly gaining scientific respectability and support.The recent surge of interest in astrobiology has led to a spate of books in astrobiology-combining astronomy and biology-but in most of these, cometary panspermia is dealt with only cursorily. The present book sets out the case for cometary panspermia in a cogent way, combining evidence from space science, celestial mechanics, geology and microbiology. It should be an essential part of any university course on astrobiology, and also serve as a reference textbook for researchers in the field.
Preface v1 Overview 11.1 Introduction 11.2 Cometary Panspermia 31.3 History of Panspermia 51.4 The Ultraviolet Problem 81.5 Resilience of Bacteria 91.6 Extremophiles 101.7 The Discovery of Organics in Cosmic Dust 111.8 Comets 131.9 The Origin of Life 141.10 Modern Advances 151.11 Protoplanetary Nebulae and Extra-solar Planetary Systems 161.12 Habitable Zone 202 Cosmic Dust and Life 232.1 Introduction 232.2 Constraints on Composition 252.3 Extinction by Spherical Particles 272.4 The Interstellar Extinction and Bacterial Dust 292.5 Infrared Evidence 372.6 Comet Dust and Biomaterial 402.7 The Identification of PAH and Biological Aromatics 432.8 Other Spectral Features 482.9 Fluorescence 502.10 The Origin of Organic Molecules in Space 532.11 Direct Analysis of Comet Dust 562.12 Capture of Comet Dust in the Stratosphere 583 The Origin of Comets 633.1 The Galactic Disc 643.2 The Formation of Stars 663.3 Planet Formation 693.4 The Formation of Comets 713.4.1 The structure of the comet population 713.4.2 Cornel chemistry 753.4.3 Cometary origin inferred 763.4.4 Other ideas about comet origins 794 Comets in the Galactic Environment 814.1 The Mechanism of Lithopanspermia 814.1.1 Transferring boulders between planetary systems 824.1.2 Erosion of ejected boulders 834.2 The Formation Sites of Comets 864.2.1 Origin in the planetary region 874.2.2 Origin in molecular clouds 904.2.3 Exocomets 934.3 The Sun's Orbit in the Galaxy 944.3.1 The effect of the vertical Galactic tide 954.3.2 Flux modulation due to the Sun's vertical motion 974.3.3 Perturbations by molecular clouds 1004.3.4 The effect on Oort cloud comets 1014.4 The Impact Cratering Record 1054.4.1 Impact melts in large craters 1094.4.2 Galactic periodicity 1115 Dark Comets: A Link to Panspermia 1175.1 A Mass Balance Problem 1185.1.1 Disintegration to dust 1195.1.2 Dark comets 1295.1.3 Super-dark comets 1305.2 The Impact Hazard and the Panspermia Connection 1346 Expulsion of Microbes from the Solar System 1376.1 Introduction 1376.2 Expectations from Impact Cratering Mechanisms 1376.3 Mechanisms for Ejection and Fragmentation of Boulders 1406.4 β-Meteoroids 1416.5 Protective Shielding in Small β-Meteoroids 1426.6 Carbonisation of the Surface Layers of Grains 1436.7 Radiation Pressure Effects 1446.7.1 Ratio of radiation pressure to gravity 1456.7.2 Results and dynamical considerations 1476.8 Surviving the Hazards of Galactic Cosmic Rays 1486.9 How Comets Distribute Life 1536.10 Dispersal of Life by Impacts 1547 Liquid Water in Comets 1577.1 Introduction 1577.2 Primordial Melting 1597.3 Evidence of Present-day Melting 1637.4 Results from Deep Impact 1697.5 Frozen Lake Surfaces 1787.6 Microbial Fossils in Carbonaceous Meteorites 1808 Origin of Life 1838.1 Preamble l838.2 Cometary Interiors as Incubators of Early Life 1888.3 Comparison with a Terrestrial Origin of Life 1899 Expanding Horizons of Life 193Bibliography 201Index 213
