Electrical processes take place in all planetary atmospheres. There is evidence for lightning on Venus, Jupiter, Saturn, Uranus and Neptune, it is possible on Mars and Titan, and cosmic rays ionise every atmosphere, leading to charged droplets and particles. Controversy surrounds the role of atmospheric electricity in physical climate processes on Earth; here, a comparative approach is employed to review the role of electrification in the atmospheres of other planets and their moons. This book reviews the theory, and, where available, measurements, of planetary atmospheric electricity, taken to include ion production and ion-aerosol interactions. The conditions necessary for a global atmospheric electric circuit similar to Earth s, and the likelihood of meeting these conditions in other planetary atmospheres, are briefly discussed. Atmospheric electrification is more important at planets receiving little solar radiation, increasing the relative significance of electrical forces. Nucleation onto atmospheric ions has been predicted to affect the evolution and lifetime of haze layers on Titan, Neptune and Triton. For planets closer to Earth, heating from solar radiation dominates atmospheric circulations. Mars may have a global circuit analogous to the terrestrial model, but based on electrical discharges from dust storms, and Titan may have a similar global circuit, based on transfer of charged raindrops. There is an increasing need for direct measurements of planetary atmospheric electrification, in particular on Mars, to assess the risk for future unmanned and manned missions. Theoretical understanding could be increased by cross-disciplinary work to modify and update models and parameterisations initially developed for a specific atmosphere, to make them more broadly applicable to other planetary atmospheres. The possibility of electrical processes in the atmospheres of exoplanets is also discussed."

Since Luna and Lunar Orbiter photographed the far side of the Moon, the mysterious dichotomy between the face of the Moon as we see it from Earth and the side of the Moon that is hidden has puzzled lunar scientists. As we learned more from the Apollo sample return missions and later robotic satellites, the puzzle literally deepened, showing asymmetry of the crust and mantle, all the way to the core of the Moon. This book summarizes the author's successful search for an ancient impact feature, the Near Side Megabasin of the Moon and the extensions to impact theory needed to find it. The implications of this ancient event are developed to answer many of the questions about the history of the Moon.

"Weird Worlds" is the third book in David Seargent's "Weird" series. This book assumes a basic level of astronomical understanding and concentrates on the "odd and interesting" aspects of planetary bodies, including asteroids and moons. From our viewpoint here on Earth, this work features the most unusual features of these worlds and the ways in which they appear "weird" to us. Within our own Solar System, odd facts such as the apparent reversal of the Sun in the skies of Mercury, CO2-driven fountains of dust on Mars, possible liquid water (and perhaps primitive life!) deep within the dwarf planet Ceres, and a variety of odd facts about the planetary moons are all discussed. A special chapter is devoted to Saturn's giant moon Titan, and its methane-based weather system and "hydrological" cycle. This chapter also includes recent speculation on the possibility of methane-based organisms and the form that these might take, if they really do exist. Beyond our Solar System, the book looks at the range of worlds discovered and hypothesized. In "Weird Worlds," the author discusses planets where temperatures are so high that it rains molten iron, and others so cold that liquid methane floods across plains of ice! Worlds are described where the lightest element acts like a metal and where winds blow at thousands of miles per hour - as well as possible planets whose orbits are essentially parabolic. In keeping with previous titles in David Seargent's "Weird" series, "Weird Worlds" contains several projects that astronomers of all levels can undertake.

How did life originate on Earth? For over 50 years, scientists believed that life was the result of a chemical reaction involving simple molecules such as methane and ammonia cooking in a primordial soup. Recent space observations have revealed that old stars are capable of making very complex organic compounds. At some point in their evolution, stars eject those organics and spread them all over the Milky Way galaxy. There is evidence that these organic dust particles actually reached the early Solar System. Through bombardments by comets and asteroids, the young Earth inherited significant amounts of stardust. Was the development of life assisted by the arrival of these extraterrestrial materials? In this book, the author describes stunning discoveries in astronomy and solar system science made over the last 10 years that have yielded a new perspective on the origin of life. Other interesting topics discussed in this book The discovery of diamonds and other gemstones in space The origin of oil Neon signs and fluorescent lights in space Smoke from the stars Stardust in our hands Where oceans come from The possibility of bacteria in space

When in 1981 Louis and Walter Alvarez, the father and son team, unearthed a tell-tale Iridium-rich sedimentary horizon at the 65 million years-old Cretaceous-Tertiary boundary at Gubbio, Italy, their find heralded a paradigm shift in the study of terrestrial evolution. Since the 1980s the discovery and study of asteroid impact ejecta in the oldest well-preserved terrains of Western Australia and South Africa, by Don Lowe, Gary Byerly, Bruce Simonson, Scott Hassler, the author and others, and the documentation of new exposed and buried impact structures in several continents, have led to a resurgence of the idea of the catastrophism theory of Cuvier, previously largely supplanted by the uniformitarian theory of Hutton and Lyell. Several mass extinction of species events are known to have occurred in temporal proximity to large asteroid impacts, global volcanic eruptions and continental splitting. Likely links are observed between asteroid clusters and the 580 Ma acritarch radiation, end-Devonian extinction, end-Triassic extinction and end-Jurassic extinction. New discoveries of 3.5 3.2 Ga-old impact fallout units in South Africa have led Don Lowe and Gary Byerly to propose a protracted prolongation of the Late Heavy Bombardment ( 3.95-3.85 Ga) in the Earth-Moon system. Given the difficulty in identifying asteroid impact ejecta units and buried impact structures, it is likely new discoveries of impact signatures are in store, which would further profoundly alter models of terrestrial evolution..

Recent space missions to the outer solar system, Galileo (1996-2003) and Cassini-Huygens (2004-today), together with ground observations, have revealed that the moons of the outer solar system are enigmatic objects, introducing extraordinary challenges for geologists, astrobiologists, organic chemists, and planetologists. Chemical exchange exists through the different layers that form their interiors, and also from the interior to the surface. The most convincing evidence is certainly the discovery of water vapour and ice particles emerging from Enceladus's active south polar region. Evidence for exchange with a subsurface liquid ocean has also been provided by the inference of hydrated salts on the surfaces of Jupiter's moons, Europa and Ganymede, as well as the detection of sodium salts in particles originating in Enceladus's plumes. Aqueous exchange with the rocky core may also be possible, considering that 40Ar has been observed in the plumes of Enceladus during one flyby of Cassini and in the atmosphere of Titan. The ongoing CH4 replenishment in Titan's atmosphere is additional striking evidence of exchange processes within the moons.

The proposal of the School was made in 1998 to three institutions, which responded enthusiastically: The Abdus Salam International Centre for Theoretical Physics (ICTP), its main co-sponsor, the International Centre for Genetic Engineering and Biotechnology, both in Trieste, Italy, and the Chancellor's Office, Universidad Simon Bolfvar (USB). The secretarial and logistic support was provided in Trieste by the ICTP and in Caracas by USB and the IDEA Convention Center. In addition the event was generously supported by the following institutes, agencies, foundations and academies: NASA Headquarters, European Space Agency, TALVEN Programme, (Delegacion Permanente de Venezuela ante la UNESCO), The SETI Institute, Centro Latinoamericano .de Ffsica, The Third World Academy of Sciences, Academia de Ciencias Ffsicas, Matematicas y Naturales, Red Latinoamericana de Biologfa, The Planetary Society, The Latin American Academy of Sciences (Fondo ACAL), Alberto Vollmer Foundation, Inc, Fundacion J. Oro, Associated to the Catalonian Research Foundation, Red Latinoamericana de Astronomfa and Colegio Emil Friedman. A total of 36 lectures were delivered by 20 lecturers, of which 14 were from the following countries: Argentina, Mexico, Italy, Spain and the USA. Six lecturers were from the host country. In addition there were 5 chairpersons from the host country that were not participants; two participants acted as chairpersons (Pedro Benitez and Tomas Revilla).

Advances in Space Environment Research - Volume I contains the proceedings of two international workshops, the World Space Environment Forum (WSEF2002) and the High Performance Computing in Space Environment Research (HPC2002), organized by the World Institute for Space Environment Research (WISER) from 22 July to 2 August 2002 in Adelaide, Australia.
The articles in this volume review the state-of-the-art of the theoretical, computational and observational studies of the physical processes of Sun-Earth connections and Space Environment. They cover six topical areas: Sun/Heliosphere, Magnetosphere/Bow Shock, Ionosphere/Atmosphere, Space Weather/Space Climate, Space Plasma Physics/Astrophysics, and Complex/Intelligent Systems.
The authors are leading space physicists from 20 countries/regions, representing the WISER international network of research and training centers of excellence dedicated to promote cooperation in cutting-edge space environment research and training of first-rate space scientists, and to link nations for the peaceful use of the space environment.
This volume is useful for space physicists, astrophysicists and plasma physicists; and can be adopted as a reference book for advanced undergraduate and postgraduate students.

The book presents current research into the effect that environmental conditions have on volcanic eruptions and the subsequent emplacement of volcanic products. This is accomplished through a series of chapters that investigate specific environments - both terrestrial and extraterrestrial - and the expression of volcanic materials found within those settings. Current state-of-the-art numerical, analytical and computer models are used in most chapters to provide robust, quantitative insights into how volcanoes behave in different environmental settings. Readership: Upper level undergraduates and new graduates. The book is primarily a presentation of research results rather than a tutorial for the general public. Textbook or supplementary reading for courses in volcanology or comparative planetology at college/university level.

nd The 2 SORO Workshop on "Mass Supply and Flows in the Solar Corona" was held in Marciana Mariana on the island of Elba, Italy, in the week September 27 to October 1, 1993, as part of a series of workshops planned by the Solar Corona and Particles Working Group of the SOHO Science Working Team (SWT). The purpose of this workshop series is to acquaint the solar community with the capabilities of SORO, and prepare scientific projects and observing plans for the mission. This Workshop, which was at tended by more than one hundred scientists from different countries, focused on the following topics: 1) Fine Scale Structures 2) Loops and Prominences 3) Coronal Streamers 4) Coronal Roles and Solar Wind Each of these four topics was introduced by an observational and a theo retical overview highlighting the most recent advances in their area. A third review illustrated how SORO might help in solving open problems. Oral pa pers and poster presentations were followed by Working Group sessions. On the last day of the Workshop the Group Leaders reported on the activities of their Working Group. These proceedings include most of the papers presented at the Work shop, including the poster papers and Working Group reports by the Group Leaders as well as two overview papers of the SORO mission. All papers have been refereed.

NASA's Genesis mission, launched on August 8, 2001 is the fifth mission in the Discovery series. Genesis addresses questions about the materials and processes involved in the origin of the solar system by providing precise knowledge of solar isotopic and elemental compositions for comparison with the compositions of meteoritic and planetary materials. This book describes the Genesis mission, the solar wind collector materials, the solar wind concentrator and simulations of its performance, the plasma ion and electron instruments, and the way these two instruments are used to determine the solar wind flow regime on board the spacecraft. The book is of interest to all potential users of the data returned by the Genesis mission, to those studying the isotopic and chemical composition of the early solar system whose work will be influenced by the measurements made by Genesis and by all those interested in the design and implementation of space instruments to study space plasmas.

The Hatfield Photographic Lunar Atlas has been long regarded as the finest photographic lunar atlas available and remains as a model of accuracy and clarity. This fully revised version is completely updated with new maps, names and technical data. The superb large-scale photographic plates and the accompanying full-scale maps make this an exceptionally easy-to-use lunar atlas for the field or observatory.

Fans of "Asterix the Gallic" know well that the only fear of people in Brittany is that the sky falls upon their head. So it must have been a shock for them (the fans of Asterix) to learn that a horde of Physicists and Dynamicists (some of them being actually Roman - ils sont fous ces Romains!) invaded the bay of Saint-Brieuc and spend a full week conjuring all the nastiness that the sky has in reserve, revelling in the horrors hidden beyond the blue dome; they talked with delight about "asteroids", "comets" and "meteor streams"; they grinned at the idea of "artificial satellites", these pots and pans of space always ready to fall upon you; some of them said strange things about the Moon, the planets, and evoked the "rings" of Saturn or of some other of their gods. One evening, a Roman from Pisa went as far as cornering some inhabitants in the large hut they used for their witchcraft and filled them with terror by describing the fate of the poor dinosaurs victims of a particularly nasty asteroid (or was it a comet?). You will be surprized to learn that Bretons did not exact a spectacular revenge for these offenses. On the contrary.

This book focuses on the recent advances in our understanding of solar convection and activity, and on new methods and results of helioseismic diagnostics. It provides a comprehensive overview of the current status of the field and presents new ideas and approaches.

As I write this short preface, the red orb of Mars is high in the eastern sky, and is brighter than it has been for many years. Last night my telescope again revealed the strange polar hood which is a feature of the planet at this time in its cycle. Because of its current prominence in the night sky, it is a very appropriate time to bring together and reappraise what we know of Mars and look forward to the next wave of planetary exploration. The initial notion of writing a book about Mars is an exciting one; the practicalities involved in working through and completing the project are, however, more than a trifle exacting. The first problem I encountered was the sheer vastness of the library of information about Mars which now exists. The second was the natural extension of the first, that is, how best to analyse it and reach widely acceptable interpretations. I have tried to write the story of Mars in a logical and unbiased way, however, we all have our individual prejudices, and I would be less than truthful if I did not admit to personal bias here and there. With this in mind, I apologise to any authors who may feel either misinterpreted or less than adequately acknowledged. The project is now completed and has been superbly prepared by Chapman & Hall.

This volume focuses on isotopic signatures of volatile elements as tracers for evolutionary processes during the formation of the Sun and the planets from an interstellar molecular cloud and, in turn, illuminates how the isotopic compositions of the present-day solar system objects have been established.
The book is an integrated collection of articles by experts in planetary science, solar and plasma physics, astrophysics, mineralogy and chemistry that met for an interdisciplinary workshop at the International Space Science Institute in Bern in January 2002. The authors present analyses of isotope abundance ratios for volatile elements in the sun, planets, satellites, comets, meteorites and interplanetary dust particles, as well as a review of isotopic ratios in star-forming interstellar clouds. This provides insight into the physical and chemical processes in the pre-solar molecular cloud that collapsed to form the Sun and the solar accretion disk. Furthermore, information is presented on dynamical processes and conditions inside this protoplanetary disk, in particular the degree of reprocessing of interstellar solid material, the formation of solids inside the disks, and the formation of terrestrial and giant planets and their satellites. Isotopic fractionation processes discussed in this book include chemical reactions such as ion-molecule and photochemical reactions, nuclear processes inside the sun and in its atmosphere, plasma processes, gravitational escape of gases from planetary atmospheres exposed to the solar wind and solar radiation, thermodynamic processes, a variety of accretion and adsorption processes and mixing of material from the interstellar environment with the material of the evolving solar system.
The volume is intended to provide active researchers in the fields of planetary science and space physics with an up-to-date status report on the topic, and also to serve graduate students with introductory material into the field.

Magnetic energy release plays an important role in a wide variety of cosmic objects such as the Sun, stellar coronae, stellar and galactic accretion disks and pulsars. The observed radio, X-ray and gamma-ray emission often directly results from magnetic flares', implying that these processes are spatially fragmented and of an impulsive nature. A true understanding of these processes requires a combined magnetohydrodynamical and plasma physical approach. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics provides a comprehensive, interdisciplinary summary of magnetic energy release in the Sun and stars, in accretion disks, in pulsar magnetospheres and in laboratory plasmas. These proceedings include papers on both theoretical and observational aspects. Fragmented Energy Release in Sun and Stars: the Interface between MHD and Plasma Physics is for researchers in the fields of solar physics, stellar astrophysics and (laboratory) plasma physics and is a useful resource book for graduate level astrophysics courses.

In June of 1996, at the idyllic seaside resort of Guaruja, Brazil, a renowned group of researchers in space and astrophysical plasmas met to provide a forum on Advanced Topics on Astrophysical and Space Plasmas at a school consisting of some 60 students and teachers, mainly from Brazil and Argentina, but also from all the other parts of the globe. The purpose was to provide an update on the latest theories, observations, and simulations of space-astrophysical plasma phenomena. The topics covered included space plasma mechanisms for particle acceleration, nonthermal emission in cosmic plasma, magnetohydrodynamic instabilities in solar, interstellar, and other cosmic objects, magnetic field line reconnection and merging, the nonlinear and often chaotic structure of astrophysical plasmas, and the advances in high performance supercomputing resources to replicate the observed phenomena. The lectures were presented by Professor Mark Birkinshaw of the Harvard-Smithsonian Center for Astrophysics and the University of Bristol; Dr Anthony Peratt, Los Alamos National Laboratory Scientific Advisor to the United States Department of Energy; Dr Dieter Biskamp of the Max Planck Institute for Plasma Physics, Garching, Germany; Professor Donald Melrose, Director, Centre for Theoretical Astrophysics, University of Sydney, Australia; Professor Abraham Chian of the National Institute for Space Research, Brazil; and Professor Nelson Fiedler-Ferrara of the University of Sao Paulo, Brazil. As summarized by Professor Reuven Opher, Institute of Astronomy and Geophysics, University of Sao Paulo, the advanced or interested student of space and astrophysical plasmas will find reference to nearly all modern aspects in the field of Plasma Astrophysics and Cosmology in the presented lectures.

Collision-or interaction-induced spectroscopy refers to radiative transitions, which are forbidden in free atoms or molecules, but which occur in clusters of interacting atoms or molecules. The most common phenomena are induced absorption, in the infrared region, and induced light scattering, which involves inelastic scattering of visible laser light. The particle interactions giving rise to the necessary induced dipole moments and polarizabilities are modelled at long range by multipole expansions; at short range, electron overlap and exchange mechanisms come into play. Information on atomic and molecular interactions and dynamics in dense media on a picosecond timescale may be drawn from the spectra. Collision-induced absorption in the infrared was discovered at the University of Toronto in 1949 by Crawford, Welsh and Locke who studied liquid O and N. Through the 1950s and 1960s, 2 2 experimental elucidation of the phenomenon, particularly in gases, continued and theoretical underpinnings were established. In the late 1960s, the related phenomenon of collision-induced light scattering was first observed in compressed inert gases. In 1978, an 'Enrico Fermi' Summer School was held at Varenna, Italy, under the directorship of J. Van Kranendonk. The lectures, there, reviewed activity from the previous two decades, during which the approach to the subject had not changed greatly. In 1983, a highly successful NATO Advanced Research Workshop was held at Bonas, France, under the directorship of G. Birnbaum. An important outcome of that meeting was the demonstration of the maturity and sophistication of current experimental and theoretical techniques.

Les deuxiernes "Rencontres de l'Observatoire", qui ont eu lieu a l'Observatoire de Paris a Meudon du 10 au 14 Janvier 2000, ont reuni autour du theme "Problernes ernergents en physique de I'espace" 120 physiciens et astrophysiciens venus d'une vingtaine de pays differents. Nous avons voulu honorer a cette occasion Jean-Louis Steinberg pour ses con- tributions majeures a la recherche spatiale, ala radioastronomie et a la physique de I'espace. L'approche explicitement pluridisciplinaire de ce colloque, qui ne s'est pas laisse confiner dans les limites etroites de la physique spatiale ni dans celles imposees par certains programmes officiels, suit l'esprit de sa carriere scientifique: sortir des limites des sujets deja etudies ou sur Ie point de l'etre, et appliquer les connaissances acquises pour explorer de nouveaux domaines. Ce dernier quart de siecle a vu une croissance vertigineuse des performances spatiales. La technologie moderne ne perrnet pas encore de jongler avec les univers comme Ie prestidigitateur de Grandville (Grandville, Un autre monde, ed. H. Four- nier, Paris, 1844); mais quelques decades ont suffi pour voir des instruments soph- istiques explorer les frontieres du systerne solaire, et la cornmunaute de la recher- che spatiale a depasse rapidement Ie sujet etroit de I'environnement soleil-terre pour s'interesser a I'ensemble de l'heliosphere, OU les memes processus physiques sont a I'ceuvre.

IAU Colloquium 165, Dynamics and Astrometry of Natural and Artificial Celestial Bodies, was held in Poznan, Poland, in July 1996, bringing together over 200 scientists from 27 countries who discussed their work in 179 oral and poster presentations. The present volume contains 83 of the papers presented at the meeting. The meeting brought together specialists from diverse fields who focused on the very close collaboration between dynamics and astrometry, where one discipline contributes to the progress of the other. The oral sessions were organized into general categories pertaining to: solar system dynamics; new observational techniques, catalogues, and astrometry; dynamics and observational problems of artificial satellites and space debris; rotation of solar system objects; reference systems and astronomical standards; new mathematical techniques; and three all-day poster sessions. This volume is divided into seven parts, comprising 83 contributions, a list of participants and an index.

The book presents the most recent developments of laboratory studies in astrophysics and space research. The individual chapters review laboratory investigations under simulated space conditions, studies for the design of successful space experiments or for supporting the interpretation of astronomical and space mission recorded data. Related theoretical models, numerical simulations and in situ observations demonstrate the necessity of experimental work on the Earth's surface. The expertise of the contributing scientists covers a broad spectrum and is included in general overviews from fundamental science to recent space technology. The book intends to serve as a reference for researchers and graduate students on the most recent activities and results in laboratory astrophysics, and to give reviews of their applications in astronomy, planetology, cosmochemistry, space research and Solar System exploration.

NASA's Advanced Composition Explorer (ACE) was launched on August 25, 1997, carrying six high-resolution spectrometers that measure the abundances of the elements, isotopes, and ionic charge states of energetic nuclei in space. Data from these instruments is being used to measure and compare the composition of the solar corona, the nearby interstellar medium, and cosmic-ray sources in the Galaxy, and to study particle acceleration processes in a variety of environments. ACE also includes three instruments that monitor solar wind and energetic particle activity near the inner Lagrangian point, "1.5 million kilometers sunward of Earth, and provide continuous, real-time data to NOAA for use in forecasting space weather. Eleven of the articles in this volume review scientific progress and outline questions that ACE will address in solar, space-plasma, and cosmic-ray physics. Other articles describe the ACE spacecraft, the real-time solar-wind system, and the instruments used to measure energetic particle composition.

Overview xiii COMETS IN PERSON 1 A Comet Passes 3 COMETS IN GENERAL 2 Anatomy of a Ghost 27 3 Dirty Snowballs and the Nurseries of Leviathans 51 4 The Spectacular Deaths of Comets 61 5 Swords of Damocles 86 6 Observing and Discovering Comets 110 HALLEY AND THE SHORT PERIOD COMETS 7 Halley and Its Periodic Kin 133 8 Through the Ages with Halley's Comet 157 COMETS WILD 9 What Makes a Comet Great? 197 10 The Comets Before 1700 204 11 The Comets from 1700 to 1995 229 vii viii COMET OF THE CENTURY THE LATEST GREATS 12 The Grand Approach of Comet Hale-Bopp 273 13 Hyakutake Lightning 291 14 A Narrative Calendar for Observing Hale-Bopp 305 15 Comet of the Century 328 Appendix A: Periodic Comet Numbers 331 Appendix B: Great Comets in History 335 AppendixC: Closest Comets in History 339 Appendix D: Celestial Coordinates 344 Appendix E: Orbital Elements 346 Appendix F: Comet Brightness Formula and Estimating Brightness 348 AppendixG: How to Report a Comet Discovery 351 AppendixH: Ephemeris for Comet Hale-Bopp 354 Glossary 359 Sources of Information 367 Credits 371 Generaiindex 373 Comet Index 381 PRtl7ACt This book may be loaded with a richness of facts, but what it's about, through and through, is simple and blazing: the way comets, throughout history, and up to the present, have stirred the human spirit.

J 2 J. MICHAEL SHl: LL, HARLEY A. THRO: \SOX, JR., A: '>D S. ALAN STER: \3 I University of Colorado, Dept. of Astrophysical. Planetary, &. Atmospheric Sciences 2 University of Wyoming and KASA Headquarters, Code SR 3 Southwest Research Institute, Boulder Office On May 15-17. 1995, three Rocky Motultain research institutions hosted a confererJce to dis cuss the scientific basis, teclmological options, and programmatic implications of a large-scale effort to find and study Earth-like planets outside the Solar System. Our workshop attracted scientists, erJgineers, space agency administrators, and the public media to discuss and debate the most promising teclmological options and opportunities. Major programs and proposals to search for and study exo-planets were preserJted and discussed. In addition, our meeting - incided .with NASA's "roadmap" study for the Exploration of Neighboring Planetary Systems ( "'\PS). Our meeting was the first international confererJce on this subject, affording an op portunity for several members of this study to participate in the debates over new technologies. Our meeting proyed to be timely. Shortly thereafter, in late 199.5 and early 1996, two groups of astronomers annotulced the first discoveries of planetary companions to nearby stars. using high-precision radial velocity measuremerJts to detect the gravitational reflex motion of the star. The first three detections include a Jupiter-mass companion to the solar-like star. 51 Pegasi, and two remarkable objects of mass at least 2. 3 and 6."