Symposium for the COSPAR Scientific Assembly
in collaboration with the
International Astronautical Congress (IAC)
at the World Space Congress -- Houston, 2002

COSPAR Commission D; IAF; IAU Commission 49

Symposium Summary

Report by: Eberhard Möbius
Space Science Center, University of New Hampshire
Durham, NH, U.S.A.

This symposium was dedicated to two of our valued colleagues and friends, who would have been active participants in our discussions. Daniel Rucinski, who has been instrumental in the modeling of the interstellar gas in the inner heliosphere and has predicted the observation of doubly charged He pickup ions - now providing for a very accurate method to derive the interstellar helium density, passed away quite unexpectedly in March 2002. Robert Forward, who had actually agreed to give the key presentation on solar sailing techniques and who is widely known as an enthusiastic and innovative promoter of interstellar travel, learned only a few months ago that he was terminally ill and passed away two weeks before the World Space Congress. We miss both of them greatly.

Over the past decade there has been explosive growth in interest and observations con-cerning the structure and boundaries of the heliosphere, our galactic neighborhood, and mutual interactions: Voyager I is approaching the termination shock. Ulysses has surveyed the inner heliosphere in 3-D over one solar cycle. ACE, EUVE, IMAGE, SAMPEX, SOHO and WIND sample inflowing interstellar material (galactic and anomalous cosmic rays, neutrals, pick-up ions and dust) and the outflowing solar wind with increasing precision. The first astrospheres of nearby stars have been identified and studied. A first mission to the heliospheric boundary and into the Local Interstellar Cloud (LIC) proper is being seriously studied. Based on this progress the Symposium “To the Edge of the Solar System and Beyond” successfully brought together space scientists and astrophysicists, as well as engineers who work on mission, propulsion and instrumentation concepts. Likewise, the conveners have come together from these disciplines, representing the co-sponsorship by COSPAR, IAF and IAU. All sessions, including the poster session, were extremely rich, lively and filled with substantial discussion. Although this symposium carried into Saturday morning, all sessions were well attended. An attempt to summarize what has been presented and discussed in less than two pages must necessarily be incomplete. Therefore, just a few highlights will be mentioned below.

The Symposium started with a historical overview by Hans Fahr, which highlighted our current understanding of the heliosphere and its interaction with the local interstellar medium. In their highly appreciated overviews on interstellar properties from an astrophysical perspective, John Dickey and Ron Reynolds built an important bridge to the potential of local observations. They surprised the audience with the interesting possibility that in-situ observations may turn up some variations of the properties within the not too distant future, if observations become accurate enough (i.e. on the order of 10%) and can be maintained continuously on the scale of 10’s of years. Rosine Lallement, George Gloeckler and Manfred Witte showed that a coordinated effort between observations and modeling of interstellar helium has been very successful. Neutral atom, UV scattering, and pickup ion observations can now be modeled with a common physical parameter set, which is consistent with results from interstellar absorption measurements of our local neighborhood. Also the increasing slowdown of the solar wind, as the Voyager spacecraft move outward, due to pickup interactions with interstellar neutrals, leads to constraints on the hydrogen density consistent with those obtained from pickup ion observations, as discussed by John Richardson. This very visible convergence of previously widely varying results may indeed open the possibility to look for temporal changes as the solar system travels through its neighborhood. As pointed out by John Slavin and Priscilla Frisch, modeling of the ionization states together with the elemental composition from pickup ions and ACRs provide strong constraints on the radiation environment of the solar system.

Remarkable progress in the understanding of further acceleration of interstellar ions in ACRs (Berndt Klecker), of the transport and modulation of galactic cosmic rays (Stephan Ferreira), and of the sensing of the boundary regions with radio and energetic neutral atoms (Andrzeij Czechowski) were reported. In addition, much improved optical observation techniques have extended our firm knowledge about solar system objects beyond Pluto into the Kuiper Belt (Tadashi Mukai), and dust not only of solar system origin is being successfully probed in-situ. The scientific discussions were concluded with an amazing account of what has been already learned from sensing the slowdown of interstellar gas in the bow wave region of nearby stars using absorption in the Lyman a line. Brian Wood presented evidence that the global parameters of stellar winds, such as the total outflow, can be reliably compared with the solar wind, which allows valuable insight into the relation of stellar activity and winds with the evolution of stars.

The technological section was initiated by Richard Mewaldt with an overview of the objectives and the concept for an interstellar probe. Although enormous progress is being made and can be expected in the future with observations inside the heliosphere, the plasma component of the interstellar gas, the magnetic field, low energy galactic cosmic rays and low mass dust particles will only become accessible with a probe into the LIC proper. Michael Gruntman reminded us that, while it will be extremely important to miniaturize instrumentation to enable such a mission and get maximum return, all apertures important for the collection of the information cannot be miniaturized because of Liouville’s Theorem. Therefore, it is extremely important to concentrate on those observations that can only be made outside. Colin McInnes gave us an account of where the currently favored propulsion technique of solar sailing is right now. Rapid progress can be seen in the development of thin materials and necessary system technologies, and tests are underway, even with commercial backing. However, a test bed mission with realistic sizing is required. A Symposium on “Missions to the Outer Solar System and Beyond” in Aosta, Italy, July 2004 (Contact: Giancarlo Genta,, may provide an upcoming discussion forum.

The participants went away with satisfying confirmation that a true dialogue between space science, representing local measurements within our home system, and astrophysicists, representing observations on the grand scale of our galaxy, has started in earnest. The commitment was made to follow up with more dedicated meetings in the near future. It has also become very clear that further progress in this field requires patient observations on a time scale of more than the full solar cycle (> 22 years). First and foremost, the current assets of heliospheric spacecraft must be kept functional until improved data start to flow. Second, the emerging knowledge suggests a variety of new observations inside the heliosphere, including neutral gas, pickup ion, energetic particle and fields, which can be implemented with moderate missions. Finally, the community needs to embark on a real interstellar probe mission, whose scope, shape and technologies are emerging now.

Convener Teaqm: E. Möbius (MSO, COSPAR), G. Vulpetti (Convener, IAF), I. Cairns (COSPAR), H. Fichtner (COSPAR), P. Frisch (COSPAR, IAU), G. Genta (IAF), A. Hansson (IAF), B. Heber (COSPAR), V. Izmodenov (COSPAR), L. Johnson (IAF), I. Mann (COSPAR), G. Matloff (IAF), M. Potgieter (COSPAR), K. Scherer (COSPAR), S. Spangler (COSPAR/IAU), F. Verheest (IAU)