This report is the summary of a workshop held in May 2003 by the Space Studies Board's Committee on Solar and Space Physics to synthesize understanding of the physics of the outer heliosphere and the critical role played by the local interstellar medium (LISM) and to identify directions for the further exploration of this challenging environment.
In summary, we can conclude that the contributions of the different ionization processes to the total ionization rate for the most abundant interstellar species are basically known. The ionization of the noble gases He and Ne is almost completely dominated by photoionization, whereas for H charge-exchange with the solar wind is most important. For other species, such as 0 and Ar, both processes contribute significantly. Electron impact ionization can typically contribute by '" 10% to the total rate in the inner Solar System. Because direct measurements of the solar EUV flux are not yet continuously available, the variation of the ionization rate over the solar cycle still contains a relatively large uncertainty. The recent measurements of pickup ion distributions and of the neutral helium gas provide an independent tool to determine the total ionization rate that can be used to cross calibrate with the results obtained for the individual ionization processes. Acknowledgements The authors are grateful to M. Allen for supplying us with new data on photoioniza tion cross-sections compiled by him. We thank also M. Gruntman for drawing our attention to and support in collecting the most recent data on charge-exchange cross-sections. D. R. was supported by grant No. 2 P03C. 004. 09 from the Com mittee for Scientific Research (Poland). This work was also supported in part through NASA contract NAS7-918, NSF Grant INT-911637, NASA Grant NAGW- 2579.
"The Heliosphere in the Local Interstellar Medium", the Proceedings of the First ISSI Workshop 6-10 November 1995, Bern, Switzerland, edited by R. von Steiger, R. Lallement, and M.A. Lee and published in 1996, was the first International Space Science Institute (ISSI) book in the Space Sciences Series. This book covers the knowledge gained in the subsequent 27 years that revolutionized our understanding of the interaction of the heliosphere with the very local interstellar medium (VLISM). Entirely new regions of space have been explored! The Voyagers both crossed the termination shock, passed through the heliosheath, crossed the heliopause, and entered the interstellar medium. New Horizons was launched with more modern instrumentation and explores low-latitude regions of the outer heliosphere. Energetic neutral atoms observed by IBEX and CASSINI allowed exploration of the heliosphere over the whole sky. The initial reconnaissance of the heliosphere and VLISM is complete with in situ measurements, observations of energetic neutral atoms (ENAs), neutral VLISM H and He, UV emissions, and interstellar dust. This book is a collection reviews from experts in the many aspects of this field that describe the current state of knowledge of the heliosphere’s interaction with the interstellar medium, puzzles yet to be solved, and future plans to continue these studies.
Knowledge about the outer heliosphere and the interstellar medium, which were long treated as two separate fields, has improved dramatically over the past 25 years as a consequence of recent developments: The discovery of interstellar pickup ions and neutral helium inside the heliosphere, the determination of the interstellar hydrogen distribution in the heliosphere obtained using backscattered solar Lyman-alpha radiation, the prediction and subsequent detection of the hydrogen wall just outside of the heliopause, the development of detailed global models for the interaction of solar wind plasma with the interstellar medium, and most recently, direct in-situ plasma and field measurements inside of the heliosheath. At the same time, our understanding of the nearby galactic environment, including the composition and dynamics of the warm gas clouds and hot gas in the local bubble, has benefited greatly from absorption-line spectroscopy using nearby stars as background sources and dynamic modeling. The present volume provides a synopsis of these developments organised into seven sections: Dominant physical processes in the termination shock and heliosheath, three-dimensional shape and structure of the dynamic heliosphere, relation of the plasmas and dust inside and outside of the heliosphere, origin and properties of the very local interstellar medium, energy and pressure equilibria in the local bubble, physical processes in the multiphase interstellar medium inside of the local bubble, and the roles that magnetic fields play in the outer heliosphere and the local bubble. The last theme is probably the most basic of all as magnetic fields play important roles in most of the phenomena discussed here. The volume concludes with four papers providing the "big picture" by looking at the time evolution of both the heliosphere and the local bubble, looking beyond the local bubble, and finally addressing the challenges in modeling the interface between the two media.
Written by experts who created the field, this volume explores uncharted scientific territory, with articles discussing the effect of our galactic environment on the heliosphere, planetary system and Earth. Leading experts in diverse fields discuss the physical changes expected as the heliosphere adjusts to its galactic environment. Topics include the interaction between solar wind and interstellar dust and gas, cosmic ray modulation, magnetospheres, variations in the solar environment, and the cosmic ray isotope record preserved in paleoclimate data.
The eleventh COSPAR colloquium The Outer Heliosphere: The Next Frontiers was held in Potsdam, Germany, from 24-28 July, 2000, and is the second dedicated to this subject after the first one held in Warsaw, Poland in 1989. Roughly a century has passed after the first ideas by Oliver Lodge, George Francis Fitzgerald and Kristan Birkeland about particle clouds emanating from the Sun and interacting with the Earth environment. Only a few decades after the formulation of the concepts of a continuous solar corpuscular radiation by Ludwig Bierman and a solar wind by Eugene Parker, heliospheric physics has evolved into an important branch of astrophysical research. Numerous spacecraft missions have increased the knowledge about the heliosphere tremendously. Now, at the beginning of a new millenium it seems possible, by newly developed propulasion technologies to send a spacecraft beyond the boundaries of the heliosphere. Such an Interstellar Proce will start the in-situ exploration of interstellar space and, thus, can be considered as the first true astrophysical spacecraft. The year 2000 appeared to be a highly welcome occassion to review the achievements since the last COSPAR Colloquia 11 years ago, to summarize the present developments and to give new impulse for future activities in heliospheric research.
