National Aeronautics and Space Administration Planetary Geology in the 1980s NASA SP - 467 Planetary Geology in the 1980s Joseph Veverka Cornell University Prepared for NASA Office of Space Science and Applications Scientific and Technical Information Branch 1985 NASA National Pieronautics and Space Administration Washington, DC Planetary Geology Working Group (PGWG) (1981-1982) Joseph Boyce Dag Nummedal NASA Headquarters, Dept. of Geology Code EL Louisiana State University Washington, DC 20546 Baton Rouge, LA 70803 Michael Carr Stephen Saunders USGS Jet Propulsion Laboratory, MS 345 Middlefield Road 183150 Menlo Park, CA 94025 4800 Oak Grove Drive Pasadena, CA 91103 Mark Cintala Dept. of Geological Sciences Eugene Shoemaker Brown University USGS Providence, RI 02912 2255 North Gemini Drive Flagstaff, AZ 86001 Merton E. Davies RAND Corporation Robert Strom 1700 Main Street University of Arizona Santa Monica, CA 90406 Lunar and Planetary Laboratory Tucson, AZ 85721 Everett Gibson Code TN7 Joseph Veverka, Chairman Johnson Space Center 312 Space Sciences Houston, TX 77058 Cornell University Ithaca, NY 14853 Ronald Greeley Arizona State University Donald Wise Dept. of Geology Dept. of Geology Tem~e.. AZ 85821 University of Massachusetts ~mherst,MA 01002 Kenneth Hamblin Brigham Young University Geology Department Provo, Utah 84602 Library of Congress Cataloging in Publication Data Main entry under title: Planetary geology in the 1980s. (NASA SP ; 467) Includes bibliographical rcfbrenccs. 1. Planets-Geology. I. i'cvrrka, .Joseph. 11. Series. QB603.G46P55 1988 559.9 88-1 6350 For sale by the National Technical Information Service, Springfield, VA 22151 Acknowledgments The original version of this report was written between 1981 and 1982 by members of the Planetary Geology Working Group with much advice and some participation from our colleagues. While the report represents a group effort, special thanks are due to the following individuals for drafting the original versions of the chapters or sections indicated: M. Carr and R. Greeley (Chapter 1); D. Wise (Section 2.1); M. Carr (Section 2.2); M. Cintala and J. Head (Section 2.3); R. Greeley (Section 2.4); D. Nummedal and V. Baker (Section 2.5); V. Hamblin (Section 2.6); R. Greeley (Section 2.7); R. Strom and E. Shoemaker (Chapter 3); E. Gibson and F. Fanale (Chapter 4); S. Saunders and J. Head (Chapter 5); M. Davies (Chapter 6). J. Veverka Preface This is the third document in a chronological series. The first appeared in 1970 at the request of NASA's former Planetology Program under the title, "A Strategy for Geologic Exploration of the Planets," edited by M. H. Carr and published as United States Geological Survey Circular No. 640. Then, as now, the objectives were to define the major goals of planetary geology and to set forth methods of meeting these goals. In 1976, the Carr study was updat- ed with the publication of A Geologzcal Basis for the Exploration of the Planets, edited by R. Greeley and M. H. Carr (NASA SP-417). The purpose of the present report is to once more provide an update and a future projection, this time into the 1980s. The basic objectives of the original strategy laid out in 1970 and in 1976 have changed little. Rather, it is our approach to realizing these goals that has matured and expanded. Now that Voyager has ventured beyond the asteroid belt into the realm of the outer planets, we have become keenly aware that the detailed study of satellites can teach us much about the geologic evolution of solid bodies in general. When the 1976 report was written, the bizarre nature of Titan's surface was hardly suspected; we were not aware of the intense volcanic activity of 10, or of the possibility that Neptune's Triton may have an ocean of liquid nitrogen. Another new emphasis that will be found in this report concerns the developing perception that the investigation of small bodies-asteroids, comets, and small satellites-can reveal much about the processes that were important during the earliest stages of the solar system's history. The en- hanced emphasis on satellites and small bodies does not imply that our traditional interest in the geology of Earthlike planets has de- creased; rather, it is a sign that as our discipline grows we are able vii to assimilate more and more diverse information in building a truer picture of the geologic evolution of the planets. We certainly expect that the 1980s will see a continuation of the vigorous effort to decipher the complex geologic history of Mars revealed by the Viking data. We also anticipate that as the quality of our geologic information concerning Venus continues to improve, a major goal of planetary geology research will be to understand the distinct evolutionary paths of Earth and Venus-two planets which at first sight appear to be similar in many of their bulk physical properties. As before, this report is not concerned with advocating any particular spacecraft mission, or series of missions, nor does it outline a sequence of solar system exploration programs. Rather, it is restricted to defining the kinds of experiments, observations, and measurements that need be made by Ear~h-based,Earth-orbit, and spacecraft exploration techniques to address major issues of con- cern to planetary geology. It also discusses important goals of data analysis and data synthesis in the area of planetary geology. This document was written by the Planetary Geology Working Group during 1981-1982. The Group attempted to produce a consensus document based on drafts of individual chapters and sections written by specific members (the individual contributions are identified in the Ac- knowledgments). We also received numerous comments on several draft versions of the report from many of our colleagues; we hope that this helpful criticism has enabled us to maintain a balanced and a represen- tative perspective throughout this document. J. Veverka .. Vlll Table of Contents 1. Introduction .......................................................................... 1.1 Relevance of Planetary Geology .................................... 1.1.1. Origin and Evolution of the Solar System ........ 1.1.2. Origin and Evolution of Life ............................. 1.1.3. Our Terrestrial Environment ............................ 1.2 The Planetary Geology Approach .................................. 1.2.1. Present Geologic State ...................................... 1.2.2. Geological Evolution of Planets ........................ 1.3 Comparative Planetology ............................................... 2 . Surface Features and Processes ............................................ Structural Geology and Tectonics ................................. 2.1.1. Basic Questions ................................................. 2.1.2. Geologic Maps ................................................... 2.1.3. Experimental Stress/Strain Studies ................... 2.1.4. Stress Field Indicators ....................................... 2.1.5. Tectonic Energy and the Generation of Stress Fields .............................................................. 2.1.6. Methodology ...................................................... 2.1.7. Summary ............................................................ 2.2 Volcanism ....................................................................... 2.2.1. Geomorphology of Volcanic Landforms ........... 2.2.2. Modeling of Volcanic Processes ........................ 2.2.3. Experimental Petrology ..................................... 2.2.4. Summary ............................................................ 2.3 Cratering ......................................................................... 28 2.3.1. Impact Cratering: An Introduction ................... 28 2.3.2. Methods of Study .............................................. 30 2.3.3. Craters in Geologic Studies: Some Established and Emerging Uses ........................................ 32 2.3.4. Persistent Problems and Unanswered Questions ....................................................... 34 2.3.5. Summary ............................................................ 36 2.4 Eolian Processes ............................................................. 36 2.4.1. Review of Eolian Activity on the Planets .......... 37 2.4.2. Relevance of Eolian Studies to Planetary Geology .......................................................... 41 2.4.3. Suggested Approach for Investigating Eolian Processes ........................................................ 46 2.4.4. Summary ............................................................ 47 2.5 Fluvial Processes ............................................................. 49 2.5.1. Water as a Geologic Agent ................................ 49 2.5.2. Dynamics of Fluvial Sedimentation ................... 50 2.5.3. Channel and Valley Morphology on Mars ........ 53 2.5.4. Summary ............................................................ 59 2.6 Mass Movement .............................................................. 59 2.6.1. Mass Movement on Earth .................................. 60 2.6.2. Mass Movement on the Moon and Mercury ..... 61 2.6.3. Mass Movement on Mars ................................... 61 2.6.4. Mass Movement on Other Bodies ..................... 62 2.6.5. Summary ............................................................ 63 2.7 Glacial and Periglacial Processes ................................... 64 2.7.1. Physical Properties of Water Ice of Interest to Geology .........................................................