Failed Stars and Super Planets

A Report Based on the January 1998 Workshop on Substellar-Mass Objects

SPACE STUDIES BOARD

NATIONAL RESEARCH COUNCIL



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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects Failed Stars and Super Planets A Report Based on the January 1998 Workshop on Substellar-Mass Objects SPACE STUDIES BOARD NATIONAL RESEARCH COUNCIL

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects Failed Stars and Super Planets A Report Based on the January 1998 Workshop on Substellar-Mass Objects Steering Group for the Workshop on Substellar-Mass Objects Space Studies Board Commission on Physical Sciences, Mathematics, and Applications National Research Council National Academy Press Washington, D.C. 1998

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the steering group responsible for the report were chosen for their special competences and with regard for appropriate balance. The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council. Support for this project was provided by Contract NASW 96013 between the National Academy of Sciences and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsor. Copyright 1998 by the National Academy of Sciences. All rights reserved. COVER: An image of the star Gliese 229A and its brown dwarf companion. Gliese 229B (lower right), obtained with a cryogenically cooled infrared coronagraph (see Figure 1.2 for details). Image courtesy of Robert H. Brown and David Trilling, University of Arizona, and Christ Ftaclas, Michigan Technical University. Copies of this report are available free of charge from: Space Studies Board National Research Council 2101 Constitution Avenue, NW Washington, DC 20418 Printed in the United States of America

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects STEERING GROUP FOR THE WORKSHOP ON SUBSTELLAR-MASS OBJECTS JONATHAN I. LUNINE, University of Arizona, Chair WILLIAM COCHRAN, University of Texas, Austin ANDREW GOULD, Ohio State University CAITLIN GRIFFITH, Northern Arizona University SHRINIVAS KULKARNI, California Institute of Technology D.N.C. LIN, University of California, Santa Cruz GERALD SCHUBERT, University of California, Los Angeles MICHAEL S. TURNER, University of Chicago Staff DAVID H. SMITH, Study Director JACQUELINE D. ALLEN, Senior Program Assistant SHARON S. SEAWARD, Project Assistant

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects SPACE STUDIES BOARD CLAUDE R. CANIZARES, Massachusetts Institute of Technology, Chair MARK R. ABBOTT, Oregon State University FRAN BAGENAL, University of Colorado, Boulder DANIEL N. BAKER, University of Colorado, Boulder LAWRENCE BOGORAD,* Harvard University DONALD E. BROWNLEE,* University of Washington ROBERT E. CLELAND, University of Washington GERALD ELVERUM, JR., TRW Space and Technology Group ANTHONY W. ENGLAND,* University of Michigan MARILYN L. FOGEL, Carnegie Institution of Washington RONALD GREELEY, Arizona State University BILL GREEN, former member, U.S. House of Representatives CHRISTIAN JOHANNSEN, Purdue University ANDREW H. KNOLL, Harvard University JONATHAN I. LUNINE, University of Arizona ROBERTA BALSTAD MILLER, CIESIN-Columbia University BERRIEN MOORE III,* University of New Hampshire GARY J. OLSEN, University of Illinois, Urbana MARY JANE OSBORN, University of Connecticut Health Center SIMON OSTRACH,* Case Western Reserve University MORTON B. PANISH,* AT&T Bell Laboratories (retired) CARLÉ M. PIETERS,* Brown University THOMAS A. PRINCE, California Institute of Technology PEDRO L. RUSTAN, JR., United States Air Force (retired) JOHN A. SIMPSON,* University of Chicago GEORGE L. SISCOE, Boston University EUGENE B. SKOLNIKOFF, Massachusetts Institute of Technology EDWARD M. STOLPER, California Institute of Technology NORMAN E. THAGARD, Florida State University ALAN M. TITLE, Lockheed Martin Advanced Technology Center RAYMOND VISKANTA, Purdue University PETER VOORHEES, Northwestern University ROBERT E. WILLIAMS,* Space Telescope Science Institute JOHN A. WOOD, Harvard-Smithsonian Center for Astrophysics MARC S. ALLEN, Director (through December 12, 1997) JOSEPH K. ALEXANDER, Director (from February 17, 1998) * Former member.

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS PETER M. BANKS, ERIM International, Inc., Co-chair W. CARL LINEBERGER, University of Colorado, Co-chair WILLIAM BROWDER, Princeton University LAWRENCE D. BROWN, University of Pennsylvania MARSHALL H. COHEN, California Institute of Technology RONALD G. DOUGLAS, Texas A&M University JOHN E. ESTES, University of California, Santa Barbara JERRY P. GOLLUB, Haverford College MARTHA P. HAYNES, Cornell University JOHN L. HENNESSY, Stanford University CAROL M. JANTZEN, Westinghouse Savannah River Company PAUL G. KAMINSKI, Technovation, Inc. KENNETH H. KELLER, University of Minnesota MARGARET G. KIVELSON, University of California, Los Angeles DANIEL KLEPPNER, Massachusetts Institute of Technology JOHN R. KREICK, Sanders, a Lockheed Martin Company MARSHA I. LESTER, University of Pennsylvania M. ELISABETH PATÉ-CORNELL, Stanford University NICHOLAS P. SAMIOS, Brookhaven National Laboratory CHANG-LIN TIEN, University of California, Berkeley NORMAN METZGER, Executive Director

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects This page in the original is blank.

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects Preface This report is based in part on the presentations made at the Workshop on Substellar-Mass Objects (WSMO), held under the auspices of the National Research Council's Space Studies Board (SSB), at the National Academies' Beckman Center in Irvine, California, on January 24-25, 1998. The workshop was organized by a steering group charged with the responsibility for structuring it, inviting speakers, summarizing the workshop in the form of this report, and drafting appropriate findings based upon its deliberations. The SSB initiated this study about substellar-mass objects (SMOs) in response to a request from Edward Weiler, NASA's science program director for the Astronomical Search for Origins, to address the following issues: What are the current research activities devoted to the identification and study of SMOs? What are the most compelling issues concerning near-term studies of SMOs as objects of intrinsic interest as end members of the population of stars and planets? What studies of SMOs are likely to contribute to broader goals in astrophysics and the planetary sciences such as galactic structure, star and planet formation, formation and evolution of planetary atmospheres, and the orbital evolution of many-body systems? What are the opportunities for interdisciplinary collaborations related to the study of SMOs? How can studies of SMOs augment, enhance, or enable the achievement of long-term scientific priorities such as the detection and characterization of extrasolar terrestrial planets and the identification of the missing mass in the universe? Given the cross-disciplinary nature of these topics, the steering group included members drawn from the SSB's Committee on Planetary and Lunar Exploration and the SSB's and the Board on Physics and Astronomy's Committee on Astronomy and Astrophysics. Organization of the workshop followed from a series of discussions on topics related to SMOs held by the steering group (seven of eight members present) and seven invited guests at the University of Arizona 's Lunar and Planetary Laboratory on November 10-11, 1997. The deliberations at this organizational meeting resulted in a guest list containing a balanced cross section of the community of scientists interested in SMOs. The draft guest list closely mirrored the final list of participants and included ground- and space-based observers as well as theorists interested in the formation, structure, and evolution of SMOs. The workshop itself was attended by the steering group (seven of eight members present); 21 invited speakers, including Harley Thronson from the National Aeronautics and Space Administration and Hugh M. Van Horn from the National Science Foundation; two non-presenting guests, M. Creech-Eakman and B.R. Oppenheimer; the SSB's study director; and one member of the press. The invited participants' overall response to the workshop was strongly positive; in particular, the workshop was considered to have covered well the important issues in the field over the 2 days allotted for the events. Each presenter was asked to prepare an expanded abstract of his/her presentation, and these are included verbatim in the body of the report.

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects Following the workshop, the steering group met on January 26, 1998, to discuss the presentations and to deliberate regarding formulation of the findings contained in this report. The steering group elected to organize the report along the lines of the workshop itself, for intellectual clarity and coherence. Some of the highlights of current understanding of SMOs in each of the seven topical areas of the workshop are summarized at the beginning of each of the first five chapters of this report. These summaries are followed by relevant abstracts. Given the scope of the charge, the brevity of the deliberative period, and the small size of the steering group, formulation of specific priorities and detailed recommendations was deemed inappropriate. Nevertheless, the steering group was able to address the questions motivating the workshop, formulate suggested avenues for future work, and reach agreement on a number of findings relating to how further progress in this field can be made. These issues are addressed in Chapter 6, which draws on the presentations and discussions at the workshop and the steering group's subsequent deliberations. Chapter 6 represents the views of the steering group and does not necessarily represent the views of the workshop's guest participants. Similarly, the views presented in the signed abstracts represent the opinions of their authors and are not, necessarily, those of the steering group. The material in this report contributed by the steering group was reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council's (NRC's) Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The contents of the review comments and draft manuscripts remain confidential to protect the integrity of the deliberative process. The steering group thanks reviewers Bernard Burke (Massachusetts Institute of Technology), Kim Griest (University, of California, San Diego), Ivan King (University of California, Berkeley), Geoffrey Marcy (University of California, Berkeley), and David J. Stevenson (California Institute of Technology) for many constructive comments and suggestions. Responsibility for the final content of those parts of this report not drafted by the guest presenters rests solely with the steering group and the NRC.

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Failed Stars and Super Planets: A Report Based on the January 1998 Workshop on Substellar-Mass Objects Foreword Until a few years ago, astronomers could only speculate about the existence of objects smaller than the smallest stars but larger than the giant planets of our solar system. Thanks to new technologies, clever techniques, and dogged perseverance, they can now point to the locations and quote the orbital parameters of nearly two dozen such substellar-mass objects (SMOs). New SMOs are being found every few months. These discoveries have opened a new subfield of astronomy. Sitting as it does at the intersection of planetary science and stellar astrophysics, this is an interdisciplinary activity that attracts researchers who usually attend different scientific meetings and publish in different journals. Moreover, because SMOs emit little detectable radiation, they are a form of “dark matter” of interest to cosmologists as well, whose gaze is normally focused millions of light-years beyond our Milky Way galaxy. Moreover, SMO studies are highly relevant to the popular search for extrasolar planets. Calling this area of research multidisciplinary might be even more accurate. This broad sweep of interest in SMOs is both intellectually exciting and administratively challenging—multidisciplinary activities often fall between the cracks in funding agencies (or even between agencies) and in academic institutions organized along traditional lines. The workshop whose activities are reported here captures the breadth and vigor of this young and emerging area. As evidence of the keen interest it inspires, all but one of the 21 invited speakers on the initial list accepted the offer to participate. The rapid advances of the past few years whet the appetite for more observational data and theoretical understanding. In its findings, the workshop's steering group is clearly upbeat about the prognosis for continued progress and identifies areas of particular promise. It also addresses some potential, but avoidable, pitfalls that attend this kind of multifaceted research. This is a subfield that deserves to be nurtured. Claude R. Canizares, Chair Space Studies Board

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