Johannes Geiss – författare

Comet nuclei are the most primitive bodies in the solar system. They have been created far away from the early Sun and their material properties have been altered the least since their formation. Thus, the composition and structure of comet nuclei provide the best information about the chemical and thermodynamic conditions in the nebula from which our solar system formed. In this volume, cometary experts review a broad spectrum of ideas and conclusions based on in situ measurement of Comet Halley and remote sensing observations of the recent bright Comets Hale-Bopp and Hyakutake. The chemical character of comet nuclei suggests many close similarities with the composition of interstellar clouds. It also suggests material mixing from the inner solar nebula and challenges the importance of the accretion shock in the outer nebula. The book is intended to serve as a guide for researchers and graduate students working in the field of planetology and solar system exploration. Several special indexes focus the reader's attention to detailed results and discussions. It concludes with recommendations for laboratory investigations and for advanced modeling of comets, the solar nebula, and the collapse of interstellar clouds.

Mars is about one-eighth the mass of the Earth and it may provide an analogue of what the Earth was like when it was at such an early stage of accretion. The fur­ ther growth of the Earth was sustained by major collisions with planetesimals and planets such as that which resulted in the formation ofthe Earth's moon (Hartmann and Davis, 1975; Cameron and Ward, 1976; Wetherill, 1986; Cameron and Benz, 1991). This late accretionary history, which lasted more than 50 Myr in the case of the Earth (Halliday, 2000a, b), appears to have been shorter and less catastrophic in the case of Mars (Harper et ai. , 1995; Lee and Halliday, 1997). In this article we review the basic differences between the bulk composition of Mars and the Earth and the manner in which this plays into our understanding of the timing and mechanisms of accretion and core formation. We highlight some of the evidence for early cessation of major collisional growth on Mars. Finally, we reevaluate the isotopic evidence that Mars differentiated quickly. Fundamental differences between the composition of Mars and that of other terrestrial planets are apparent from the planet's slightly lower density and from the compositions of Martian meteorites. The low density is partially explicable if there is a greater proportion of more volatile elements.

This volume, number 16 in the Space Sciences Series of ISSI, reviews the present knowledgeonmanyaspectsofthehistoryofthesolarsystem. Itfocuses onisotopic signatures ofvolatile elements as tracers for the evolutionary processes during the formation of the Sun and the planets from an interstellar molecular cloud and, in tum, illuminates how the isotopic compositions of present-day solar system ob- jects had been established. This integrated collection of articles complements the information provided by previous ISSI volumes such as From Dust to Terrestrial Planets and Chronology and Evolution of Mars, expanding the time scale for the history ofthe solar system. The convenors, Therese Encrenaz, Observatoire de Paris, Meudon; Johannes Geiss, ISSI, Bern; Reinald Kallenbach, ISSI, Bern; Konrad Mauersberger, Max- Planck-Institut fUr Kernphysik, Heidelberg; Tobias Owen, University of Hawaii, Honolulu; and Fran~ois Robert, CNRS-Museum d'Histoire Naturelle, Paris, in- vited experts in planetary science, solar and heliospheric physics, astrophysics, mineralogy, and chemistry to an interdisciplinary workshop in Bern, 14-18 Jan- uary 2002.The resulting review articles are grouped into four sections 'Sun and Protosolar Nebula', 'Outer Solar System', 'Earth, Terrestrial Planets, and Moon', and 'Isotopic FractionationProcesses'.

Mars is about one-eighth the mass of the Earth and it may provide an analogue of what the Earth was like when it was at such an early stage of accretion. The fur­ ther growth of the Earth was sustained by major collisions with planetesimals and planets such as that which resulted in the formation ofthe Earth's moon (Hartmann and Davis, 1975; Cameron and Ward, 1976; Wetherill, 1986; Cameron and Benz, 1991). This late accretionary history, which lasted more than 50 Myr in the case of the Earth (Halliday, 2000a, b), appears to have been shorter and less catastrophic in the case of Mars (Harper et ai. , 1995; Lee and Halliday, 1997). In this article we review the basic differences between the bulk composition of Mars and the Earth and the manner in which this plays into our understanding of the timing and mechanisms of accretion and core formation. We highlight some of the evidence for early cessation of major collisional growth on Mars. Finally, we reevaluate the isotopic evidence that Mars differentiated quickly. Fundamental differences between the composition of Mars and that of other terrestrial planets are apparent from the planet's slightly lower density and from the compositions of Martian meteorites. The low density is partially explicable if there is a greater proportion of more volatile elements.

One of the most attractive features of the young discipline of Space Science is that many of the original pioneers and key players involved are still available to describe their field. Hence, at this point in history we are in a unique position to gain first-hand insight into the field and its development. To this end, The Century of Space Science, a scholarly, authoritative, reference book presents a chapter-by-chapter retrospective of space science as studied in the 20th century. The level is academic and focuses on key discoveries, how these were arrived at, their scientific consequences and how these discoveries advanced the thoughts of the key players involved. With over 90 world-class contributors, such as James Van Allen, Cornelis de Jager, Eugene Parker, Reimar Lüst, and Ernst Stuhlinger, and with a Foreword by Lodewijk Woltjer (past ESO Director General), this book will be immensely useful to readers in the fields of space science, astronomy, and the history of science. Both academic institutions and researchers will find that this major reference work makes an invaluable addition to their collection.

This volume, number 16 in the Space Sciences Series of ISSI, reviews the present knowledgeonmanyaspectsofthehistoryofthesolarsystem. Itfocuses onisotopic signatures ofvolatile elements as tracers for the evolutionary processes during the formation of the Sun and the planets from an interstellar molecular cloud and, in tum, illuminates how the isotopic compositions of present-day solar system ob- jects had been established. This integrated collection of articles complements the information provided by previous ISSI volumes such as From Dust to Terrestrial Planets and Chronology and Evolution of Mars, expanding the time scale for the history ofthe solar system. The convenors, Therese Encrenaz, Observatoire de Paris, Meudon; Johannes Geiss, ISSI, Bern; Reinald Kallenbach, ISSI, Bern; Konrad Mauersberger, Max- Planck-Institut fUr Kernphysik, Heidelberg; Tobias Owen, University of Hawaii, Honolulu; and Fran~ois Robert, CNRS-Museum d'Histoire Naturelle, Paris, in- vited experts in planetary science, solar and heliospheric physics, astrophysics, mineralogy, and chemistry to an interdisciplinary workshop in Bern, 14-18 Jan- uary 2002.The resulting review articles are grouped into four sections 'Sun and Protosolar Nebula', 'Outer Solar System', 'Earth, Terrestrial Planets, and Moon', and 'Isotopic FractionationProcesses'.

Comet nuclei are the most primitive bodies in the solar system. They have been created far away from the early Sun and their material properties have been altered the least since their formation. Thus, the composition and structure of comet nuclei provide the best information about the chemical and thermodynamic conditions in the nebula from which our solar system formed. In this volume, cometary experts review a broad spectrum of ideas and conclusions based on in situ measurement of Comet Halley and remote sensing observations of the recent bright Comets Hale-Bopp and Hyakutake. The chemical character of comet nuclei suggests many close similarities with the composition of interstellar clouds. It also suggests material mixing from the inner solar nebula and challenges the importance of the accretion shock in the outer nebula. The book is intended to serve as a guide for researchers and graduate students working in the field of planetology and solar system exploration. Several special indexes focus the reader's attention to detailed results and discussions. It concludes with recommendations for laboratory investigations and for advanced modeling of comets, the solar nebula, and the collapse of interstellar clouds.

Comet nuclei are the most primitive bodies in the solar system. They have been created far away from the early Sun and their material properties have been altered the least since their formation. Thus, the composition and structure of comet nuclei provide the best information about the chemical and thermodynamic conditions in the nebula from which our solar system formed. In this volume, cometary experts review a broad spectrum of ideas and conclusions based on in situ measurement of Comet Halley and remote sensing observations of the recent bright Comets Hale-Bopp and Hyakutake. The chemical character of comet nuclei suggests many close similarities with the composition of interstellar clouds. It also suggests material mixing from the inner solar nebula and challenges the importance of the accretion shock in the outer nebula. The book is intended to serve as a guide for researchers and graduate students working in the field of planetology and solar system exploration. Several special indexes focus the reader''s attention to detailed results and discussions. It concludes with recommendations for laboratory investigations and for advanced modeling of comets, the solar nebula, and the collapse of interstellar clouds.