Comets and the Origin and Evolution of Life

Transcription

1 Comets and the Origin and Evolution of Life

2 Advances in Astrobiology and Biogeophysics springer.com This series aims to report new developments in research and teaching in the interdisciplinary fields of astrobiology and biogeophysics. This encompasses all aspects of research into the origins of life from the creation of matter to the emergence of complex life forms and the study of both structure and evolution of planetary ecosystems under a given set of astro- and geophysical parameters. The methods considered can be of theoretical, computational, experimental and observational nature. Preference will be given to proposals where the manuscript puts particular emphasis on the overall readability in view of the broad spectrum of scientific backgrounds involved in astrobiology and biogeophysics. The type of material considered for publication includes: Topical monographs Lectures on a new field, or presenting a new angle on a classical field Suitably edited research reports Compilations of selected papers from meetings that are devoted to specific topics The timeliness of a manuscript is more important than its form which may be unfinished or tentative. Publication in this new series is thus intended as a service to the international scientific community in that the publisher, Springer-Verlag, offers global promotion and distribution of documents which otherwise have a restricted readership. Once published and copyrighted, they can be documented in the scientific literature. Series Editors: Dr. André Brack Centre de Biophysique Moléculaire CNRS, Rue Charles Sadron Orléans, Cedex 2, France Brack@cnrs-orleans.fr Dr. Gerda Horneck DLR, FF-ME Radiation Biology Linder Höhe Köln, Germany Gerda.Horneck@dlr.de Prof. Dr. Michel Mayor Observatoire de Genéve 1290 Sauverny, Switzerland Michel.Mayor@obs.unige.ch Dr. Christopher P. McKay NASA Ames Research Center Moffet Field CA 94035, USA Prof. Dr. H. Stan-Lotter Institut für Genetik und Allgemeine Biologie Universität Salzburg Hellbrunnerstr Salzburg, Austria

3 Paul J. Thomas Roland D. Hicks Christopher F. Chyba Christopher P. McKay (Eds.) Comets and the Origin and Evolution of Life Second Edition With 65 Figures Including 13 Color Figures ABC

4 Paul J. Thomas University of Wisconsin Dept. of Physics and Astronomy Eau Claire WI , USA Christopher F. Chyba Center for the Study of Life in the Universe, SETI Institute 2035 Landings Drive Mountain View, CA 94043, USA Roland Dean Hicks University of Wisconsin Dept. of Physics and Astronomy Eau Claire WI , USA Christopher P. McKay Space Science Division Mail Stop 245-3, NASA Ames Research Center, Moffett Field CA 94035, USA Comet image on Front Cover: Comet Neat. Credit: Edward M. Henry; Clearview Farm Observatory; Humbird, Wisconsin. Source: < Paul J. Thomas et al., Comets and the Origin and Evolution of Life, Adv. Astrobiol. Biogeophys. (Springer, Berlin Heidelberg 2006), DOI /b Library of Congress Control Number: ISBN-10 ISBN Springer Berlin Heidelberg New York Springer Berlin Heidelberg New York This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted only under the provisions of the German Copyright Law of September 9, 1965, in its current version, and permission for use must always be obtained from Springer. Violations are liable for prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springer.com c Springer-Verlag Berlin Heidelberg 2006 Printed in The Netherlands The use of general descriptive names, registered names, trademarks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. Typesetting: by the authors and techbooks using a Springer LATEX macro package Cover design: design & production GmbH, Heidelberg Printed on acid-free paper SPIN: /techbooks

5 This volume is dedicated to the memory of Juan Oró ( ) and Carl Sagan ( ), two pioneers in the study of comets and the origins of life. Picture by Susan Magnolia Houge, c The University of Wisconsin System.

6 Preface The original volume of Comets and the Origin and Evolution of Life was published in 1997 as the product of a conference held on those topics in Eau Claire, WI. The timing of the conference seemed particularly opportune in light of the recent (1986) encounter of the Giotto and VEGA spacecraft with Comet Halley, recent improvements in the chemical analysis of interplanetary dust particles (IDPs) and chemical models of organic synthesis in meteorites and comets. In addition, the prospect of new data from spacecraft such as NASA s Comet Rendezvous/Asteroid Flyby mission (CRAF) and the joint ESA/NASA Rosetta mission promised exciting progress in our understanding of the nature of comets and their organic materials. In the 9 years since the publication of the original volume, great progress has been made in this dynamic field. Signature events include the detailed observations of Comet Hyakutake in 1996 and Comet Hale-Bopp in 1997, and new spacecraft encounters with comets: Deep Space 1 with Comet Borrelly in 2001, Stardust with Comet Wild 2 in 2004 (with coma samples to be returned to Earth in 2006), and Deep Impact with Comet Tempel 1 in There have also been disappointments: the CRAF mission was canceled, NASA s CONTOUR mission was lost shortly after launch in 2002, and the muchdelayed Rosetta mission (with mission capabilities now descoped from sample return to Earth to in situ analysis of Comet Churyumov Gerasimenko in 2014). But the editors agreed with the urging of our publishers that it was now an opportune time to update and rework the original 1997 volume. As in the original volume, we review the history of our study of comets and the origin of life while describing the current state of the field. Oró, Lazcano, and Ehrenfreund review the historical development of the key idea of this book and its predecessor that comets have played an important role in the origins of life by introducing vital prebiotic organic materials at a very early stage in Earth s history. It seems very likely now that the accumulation of the organic inventory of the Earth was likely a mix of exogenic organics with those endogenically synthesized in the early atmosphere or, perhaps, in other terrestrial or deep-sea locations. Delsemme (in an updated version of an earlier

7 VIII Preface chapter) estimates the volatile inventory brought to the early Earth during its formation by cometary impact. An important fraction of cometary material has been delivered to the Earth in the form of dust; perhaps the majority of the organic cometary material has been delivered in this way. The analysis of Antarctic Micrometeorites (AMMs), described in detail by Maurette, may provide important information on this cometary material. At the time of publication, however, a conclusive link between AMMs and comets remains to be made. While less dramatic than spacecraft missions, the continuing progress in discovering complex organic macromolecules in comets, protostars, and interstellar clouds has been spectacular since the publication of the first book. Huebner and Snyder review this active field, in particular, focusing on the discovery of many different organic molecules in the active chemical environments of the hot molecular cores of star forming regions (HMCs). Because synthesis can occur in HMCs at much faster rates than in cold interstellar clouds, they are of particular importance for the study of the organic molecules inside comets. The inevitable increase in computational power in the last decade has allowed numerical simulations of comet impacts to have increased spatial and temporal resolution. Pierazzo and Chyba present the results of recent simulations that model organic delivery to Mars, Europa, and the Moon, in addition to the Earth. As reported in the previous volume impact shocks, although high, do allow approximately 10% of the incoming organic material to survive the impact process although many uncertainties in such modeling remain, especially with the applicability of high-temperature pyrolysis data. This survivability is particularly high in the case of oblique impacts. On Mars, with its lower escape speed, higher survivability fractions are possible. The chapter by Chyba and Hand substantially updates its predecessor chapter in the 1997 volume, coauthored by Chyba and the late Carl Sagan. This chapter places the issue of impact delivery of organics by comets in the broad context of the history of the Heavy Bombardment and the very early history of the Earth. If both exogenous and endogenous sources of organics were present on the early Earth, it is of importance to attempt to compare the amounts of organics produced from either source. (Note that exogenous sources also include the synthesis of organics by impact shock and dust delivery as well as impact delivery.) Although such attempts are necessarily incomplete and limited by necessary assumptions, it seems as though atmospheric UV photolysis and delivery of IDPs probably dominated the origins of organics on the early Earth in roughly equal proportion, with other sources (e.g., hydrothermal vents and impact shocks) playing a smaller quantitative role. The original volume of Comets and the Origin and Evolution of Life also considered the role that comets and asteroids played in the destruction, or frustration, of life on Earth. In the first of three chapters linked by this theme, Zahnle and Sleep analyze the conditions under which life appeared on the Earth. These conditions were shaped by the end of the Heavy Bombardment,

8 Preface IX and the accompanying shocks and heating events, leading to rock vapor atmospheres with ocean-vaporizing consequences that would have persisted for months to millenia after each large impact. In a companion to the impact delivery analyses of Pierazzo and Chyba, Zahnle and Sleep consider the sterilizing aspect of such events on early Mars as well as on the Earth. The geological history of the early Earth is preserved only in a few locations on the Earth. Two of them are the Pilbara craton in Western Australia and the Kaapvaal craton in southern Africa. Glikson presents the current results of detailed explorations of both features with a focus on the identification of signatures of events from the early Precambrian. Among the exciting discoveries from this process are the apparent intermittent (perhaps because of impact sterilization events) appearance of stromatolites and possible connections between early impacts and hydrothermal vent activity and iron-rich sediments that may be associated with postimpact volcanism. In the final chapter liked with the theme of impact destruction of life, Morrison reviews the contemporary hazard of comet impacts. While a significant effort has been made to identify near-earth asteroids that may pose an impact threat to our civilization, identifying such threats from the comet population (which mostly resides in the outer solar system) is much more difficult. A perpetual survey will be required for such objects. If a comet is identified on an orbit that will likely result in an impact, we have to consider the possibility that a poorly determined orbit may produce a false alarm. Finally, the orbital velocities of comets, which are much higher than near-earth asteroids, present significant problems with interception and orbit change. If comet nuclei have a significant organic component, how likely is it that, in addition, they may have once contained liquid water? Podolak and Prialnik examine the role that intense internal heating from radioactive 26 Al may have played in creating temporary ( 10 5 y) liquid water environments inside comets of >10 km radius. Kissel and Krueger, in two concluding chapters, review the history and future of spacecraft missions to comets and the chemistry of interstellar and cometary dust. There are much exciting spacecraft data still to be gathered. The year 2006 will see the recovery of comet dust from the Stardust spacecraft and in 2014 Philae, the lander portion of Rosetta, will make the first softlanding on a comet nucleus. In the final chapter, Krueger and Kissel present the results of the analysis of dust from Comet Wild 2, using the CIDA instrument on the Stardust spacecraft. The results are compared with a scenario for the synthesis of organic material in cometary dust. This new volume has taken a long time to compile. The editors decided early in the process of preparation that, given the dynamic nature of this field, a limited rewrite of the previous edition would not suffice. The reader will notice a diversity of views and approaches in the chapters of the book. The editors felt that such a rapidly developing field is best served by conveying differences in ideas, and chose not to impose consensus on the authors. We

9 X Preface hope that this book encapsulates the excitement of the study of comets and the origins of life and gives some picture of the great developments in knowledge that surely lie ahead. The editors thank Dr. Christian Caron of Springer-Verlag for his constant encouragement throughout this project. The editors also thank Dr. Ramon Khanna, Ms. Birgit Muench, and Ms. Gabriele Hakuba of Springer-Verlag for their unfailing helpfulness. Dr. William Hartmann of the Southwest Research Institute gave important guidance during the planning of the book. We also, appreciate the generosity and wisdom of University of Wisconsin Eav Claire faculty and staff, Dr. Lauren Likkel, Dr. Alex Smith, Mr. John Stupak, Dr. Marty Wood, Mr. Don Zeutschel of the Office of Research and Sponsored Programs, and Mr. Susan Magnolia Hogue and Mr. Gene Leisz of the Learning and Technology Services (formerly the Media Development Center) at the University of Wisconsin Eav Claire. May 2006 P.J. Thomas R.D. Hicks C.F. Chyba C.P. Mckay

10 Contents 1 Comets and the Origin and Evolution of Life J. Oró, A. Lazcano, and P. Ehrenfreund Introduction Comets and the Origin on Life: An Idea with a Long History Chemical Evolution of Cometary Nuclei The Collisional History of the Early Solar System A Cometary Origin for the Terrestrial Volatiles? Comets and Prebiotic Synthesis Cometary Collisions and Biological Evolution References The Origin of the Atmosphere and of the Oceans A. Delsemme Introduction Hypothesis of the Volcanic Origin The Missing Primary Atmosphere The Origin of the Solar System Existence of Accretion Disks Numerical Models for a Protosolar Accretion Disk The Chondrites as Clues on Planetary Formation FromDusttoPlanets Temperature History of the Earth s Material Thermochemical Equilibrium in Solar Nebula Discussion: Was the Earth Outgassed? Formation of the Giant Planets Orbital Diffusion of Comets Chronology Chronology Discussion Observational Confirmations Cratering Record Geochemistry

11 XII Contents Geochemical Model Noble Gases Deuterium Nature of the Early Atmosphere Prebiotic Organic Syntheses Summary Verified Predictions of the Model Unverified Predictions of the Model Conclusion References Cometary Micrometeorites in Planetology, Exobiology, and Early Climatology M. Maurette Introduction Dark Micrometeorites in Blue Ices: Relationships with Hydrous Carbonaceous Chondrites Formation of the Earth s Atmosphere: Previous Scenarios Volcanism, Nebular Gases, and Comets A Wrong Neon in the Giant Asteroid? The Micrometeoritic Purity of the Earth s Atmosphere Concentrations of Volatiles in Antarctic Micrometeorites The Micrometeoritic Purity of the Earth s Atmosphere Formation of the Post-Lunar Earth s Atmosphere An Accretion Formula Born with the Moon Total Amounts of Micrometeoritic Volatiles in the Post-Lunar Atmosphere Micrometeoritic Siderophile Elements in Planetology Micrometeoritic Iridium in the Earth s Mantle A Difficult Extrapolation to the Moon and Mars Micrometeoritic Sulfur and Ferrihydrite in Exobiology Micrometeoritic Sulfur and the Worlds of Iron Sulfides andthioesters Ferrihydrite in Unmelted and Melted Micrometeorites A Post-Lunar Micrometeoritic Greenhouse Effect? Controversies About the Parent Bodies of Micrometeorites From Prospects to Unsolved Problems References Macromolecules: From Star-Forming Regions to Comets to the Origins of Life W.F. Huebner, Lewis E. Snyder Introduction Interstellar Ices Laboratory Simulations

12 Contents XIII 4.4 Observations from Massive Star-Forming Regions Current Research on Macromolecules in HMCs and Comets Sgr B2(N-LMH) Other Sources Comets Summary and Prognosis References Impact Delivery of Prebiotic Organic Matter to Planetary Surfaces E. Pierazzo, C.F. Chyba Introduction SourcesofOrganicMaterial Hydrocode Simulations Earth:SignificantDelivery Mars:BalancingFactors Europa:ImpactorLoss Amino Acids on the Moon: Impact Delivery? Summary and Conclusions References Comets and Prebiotic Organic Molecules on Early Earth C.F. Chyba, K.P. Hand The Uninhabitable Habitable Zone The Habitable Zone and Liquid Water Are the Earth s Oceans Extraterrestrial? D/H Ratios and Noble Gas Evidence The Time Window for the Origin of Life Frustration of the Origin of Life Microfossils and Stromatolites Molecular Biomarkers Carbon Isotope Fractionation Endogenous Production of Prebiotic Organic Molecules Nature of the Early Atmosphere Energy Sources and Atmospheric Organic Production Organic Production at Hydrothermal Vents TheLunarCrateringRecord A Terminal Lunar Cataclysm? Implications for the Mass Flux on Early Earth Impact Delivery of Intact Exogenous Organics Interplanetary Dust Particles and Micrometeorites Interstellar Dust Meteorites Catastrophic Airbursts Big Impacts

13 XIV Contents 6.6 Atmospheric Shock Synthesis of Organic Molecules Shocks from Meteors Shocks from Airburst Shocks from Giant Impact Plumes Postimpact Recombination Amino Acids at the K/T Boundary An Inventory of Organic Production on Early Earth Organic Sinks and Concentrations Prebiotic Organics on the Early Earth References Impacts and the Early Evolution of Life Kevin Zahnle, Norman H. Sleep Prologue Introduction TheLunarRecord Energies of Basin-Forming Impacts Crustal Contamination by Chondrites Chronology of the Late Bombardment TheLateBombardmentontheEarth Impactor Mass Distribution Scaling the Lunar Impact Record to the Earth Environmental Effects of Large Impacts on the Earth An Ocean Vaporizing Impact Imbrium on the Earth Evolutionary Filters TheLateBombardmentonMars Environmental Effects of Large Impacts on Mars Local Panspermia Conclusions Epilogue References Extraterrestrial Impact Episodes and Archaean to Early Proterozoic ( Ga) Habitats of Life A. Glikson Introduction PRE 3.8-Ga Events Post 3.8-Ga Extraterrestrial Impacts Archaean to Early Proterozoic Impacts, Pilbara, and Kaapvaal Cratons About 3.5-Ga Impact Cluster About Ga Asteroid Bombardment About Ga Impact Clusters and Associated Tsunami

14 Contents XV 8.5 Possible and Demonstrated Connections Between Extraterrestrial Impacts and Habitats of Life References The Contemporary Hazard of Comet Impacts D. Morrison Introduction Impactor Population NatureoftheHazard Penetration Through the Atmosphere Globally Catastrophic Impacts Threshold for a Globally Catastrophic Climate Perturbation HazardAnalysis Risk Reduction and Mitigation Impact Prediction Deflection or Destruction The Challenge of Comets Summary and Conclusions References The Conditions for Liquid Water in Cometary Nuclei M. Podolak, D. Prialnik Introduction Reconsidering Internal Heat Sources Radioactive Heating Amorphous Crystalline Transition Cooling Mechanisms Thermal Diffusivity Simple Physics Energy Considerations Timescales Numerical Models What Further Studies May Show References Spacecraft Missions to Comets J. Kissel, F.R. Krueger Overview The Relevance for Issues of the Origin of Life Space Missions to Comets Results and Expectations The Measurements at Halley Current Missions Future Missions Conclusions

15 XVI Contents References Interstellar and Cometary Dust in Relation to the Origin of Life F.R. Krueger, J. Kissel First In Situ Chemical Analysis of Interstellar Dust Quinone Derivatives as Main Organic Component Hydrated Dirty PAHs as Products of Radiative ChemistryinNebulae Possible Thermochemical Implications for the Accretion Process to Comets New In Situ Analysis of Cometary Dust at p/wild Corroboration of the Cometary Dust Prevalence ofnitrogenchemistry Precursors of Amino Acids, Sugars, and Some Other Building Blocks in Cosmic Dust Combined Scenario of Origin of Life with Both Dust Types Hydrolysis Mechanisms of Cometary Dust in Water Some Necessary Conditions for Systemic Chemical Self-Organization The Question of Redox Catalysis Needed Possibilities and Limitations of Heterocatalysis bymineralsurfaces Interstellar Dust and the PQQ-Enigma for Catalysis Conclusions and Further Goals References Index...341

16 List of Contributors C.F. Chyba A. Delsemme P. Ehrenfreund A. Glikson K.P. Hand W.F. Huebner J. Kissel F.R. Krueger A. Lazcano M. Maurette D. Morrison J. Oró E. Pierazzo M. Podolak D. Prialnik N.H. Sleep L.E. Snyder K. Zahnle