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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.
eberhard.moebius@unh.edu
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, genta@polito.it), 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)
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