The interaction of the solar wind with Mars is, to first order, determined by whether or not the planet has an intrinsic magnetic field.  From the very beginning of Mars exploration this question has been hotly debated.  When the first measurements were taken near Mars by Mariner 4 in 1965, a bow shock was observed by the magnetometer [Smith et al., 1965].  Its position was interpreted by some to indicate the presence of a small planetary field, while others argued against it [e.g., the review by Vaisberg, 1992, and references therein].
The next seven missions to Mars space, including the Viking mission, added only marginally to the understanding, primarily do to the lack of appropriate instrumentation carried on these spacecraft, and unsuitable trajectories.  Then the Phobos mission was launched in 1988, carrying a nearly complete suite of field and particle instruments on board.  Upon arrival in 1989, Phobos 2 entered a highly elliptical, 77 h period orbit, with periapsis at 850km altitude.  After four orbits the spacecraft was maneuvered into an 8 h period circular orbit of 6203 km altitude (2.8 Rm).  Unfortunately, after only three month contact with Phobos 2 was lost (Phobos 1 was lost during cruise), ending much too prematurely an exiting and ambitious mission.  But during its time in orbit, Phobos measurements showed that a complex and probably unique plasma environment existed around Mars.  However, it still could not been shown whether or not a planetary magnetic field was present.
This question was finally answered by the Mars Global Surveyor (MGS) mission.  After the loss of Mars Observer during its preparation for the Mars orbit insertion maneuver (1993), MGS was launched on November 7, 1996.  The primary objective of the MGS mission is to conduct a global mapping mission of Mars by performing an extended orbital study of the planet's surface, atmosphere, and gravitational and magnetic fields.
The spacecraft’s planned mapping orbit was at low altitude (about 350 km, near-circular, near-polar orbit that is Sun-synchronous with the day-side equatorial crossing at 2:00 PM local mean solar time.  To deliver the spacecraft into this orbit, aerobraking was used over a period of about 18 month (this was longer than originally planned because one of the solar panels was damaged during launch).  The extended aerobraking turned out to be a great bonus to the MAG/ER investigation, because it carried the spacecraft to about 100 km altitudes (many below 100 km) on each orbit, well below the ionospheric peak.  It was thus possible for the magnetometer to peek below the hiding cover of the ionosphere and check directly for any planetary magnetic field.
From these orbits MGS could show conclusively that no dipole-like, dynamo generated planetary field exist on Mars at present.  However, large remnant magnetic fields were detected in localized regions on the planet, indicating that a dynamo field did exist, probably until some 4 billion years ago [Acuna et al., 1999; Acuna et al., 1998; Connerney et al., 1999].  The absence of a planetary dipole filed sets stringent conditions on the solar wind/Mars interaction process, in fact it now clearly defines how we look at the near Mars plasma environment.
We knew before that the interaction was not lunar-like, because of Mars’ ionosphere, albeit the ionosphere was calculated too thin to routinely stand-off the solar wind.  We know now that the interaction is not magnetospheric, Earth-like.  However, the magnetic anomalies, larger than any seen on Earth, add a dynamic character to the interaction as they rotate into view of the solar wind every Mars rotation period.  There is thus a periodic addition of significant magnetic pressure to help standoff the solar wind.  So we know that the interaction is not purely ionospheric, Venus-like.  Rather, it is clear now that the Mars interaction with the solar wind is a complicated and dynamic mixture of all three possibilities.
It can easily be envisioned that this geometry leads to many boundaries within the Mars plasma environment.  In fact the Phobos and MGS literature is full of descriptions of boundaries found by individual instrument.  Many of the boundaries are controversial in that they where not seen by the other instruments.  Table 1 indicates the name, definition, and location of some of them.  The table indicates the complicated nature of the interaction.
MGS carried only two magnetometers and an Electron Reflectometer, and thus is blind to ion, plasma wave, and energetic particle events.  But it did gather the magnetic and electron data in great detail and with very good statistics from an optimal orbit.  Phobos 2 on the other hand, had many field and particle instruments, but took measurements at large distances and for a relatively short period of time.
The workshop has “dovetailed” the observations by Phobos and MGS, and theoretical and numerical work, to produce interpretations with greater fidelity and clarity.  Much work was expanded to integrate all the observations into a coherent picture of the Mars/solar wind interaction process.

• Papers and articles that have resulted from the workshop, published in “Mars’ Magnetism and its Interaction with the Solar Wind”, and in Space Science Reviews (Kluwer, 2004):
 “Mars Crustal Magnetism”, J. E. P. Connerney, M. H. Acuña, N. F. Ness, T. Spohn, and G. Schubert.
“The Plasma Environment of Mars”, A. F. Nagy, D. Winterhalter, K. Sauer, T. E. Cravens, S. Brecht, C. Mazelle, D. Crider, E. Kallio, A. Zakharov, E. Dubinin, M. Verigin, G. Kotova, W. I. Axford, C. Bertucci, and J. G. Trotignon.
“Bow Shock and Upstream Phenomena at Mars”, C. Mazelle, D. Winterhalter, K. Sauer, J.G. Trotignon, M.H. Acuña, K. Baumgärtel, C. Bertucci, D.A. Brain, S.H. Brecht, M. Delva, E. Dubinin, M. Øieroset, and J. Slavin.
“The Magnetic Field Pile-Up And Density Depletion in the Martian Magnetosheath: A Comparison with the Plasma Depletion Layer Upstream of the Earth’s Magnetopause”, Marit Øieroset, David L. Mitchell, Tai D. Phan, Robert. P. Lin, Dana H. Crider and Mario H. Acuña.
“Mars Global Surveyor Observations Of Solar Wind Magnetic Field Draping Around Mars”, Dana H. Crider, David A. Brain, Mario H. Acuña, Didier Vignes, Christian Mazelle, Cesar Bertucci.
“Magnetic Flux Ropes in the Martian Atmosphere: Global Characteristics”, D. Vignes, M.H. Acuña, J.E.P. Connerney, D.H. Crider, H. Reme and C. Mazelle.
“Unusually Distant Bow Shock Encounters at Mars: Analysis of the March 24, 1989 Event”, M. I. Verigin, J. Slavin, A. Szabo, G. A. Kotova, A. P. Remizov, H. Rosenbauer, S. Livi, K. Szegö, M. Tátrallyay, K. Schwingenschuh, and T.-L. Zhang.
“MarsExpress and MARSIS”, Erling Nielsen.

• Team members:

Mario Acuna, Goddard Space Flight Center/NASA, Greenbelt, USA;
Ian Axford, Max Planck Institut, Lindau, Germany;
Klaus Baumgaertel, Max Planck Institut, Lindau, Germany;
Siegfried Bauer, University of Graz, Graz, Austria;
Cesar Bertucci, Centre d'Etude Spatiale des Rayonnements/CNRS, Toulouse, France;
David Brain, University of Colorado, Boulder, USA;
Stephen Brecht, Bay Area Res Corp,  Orinda, CA 94563, USA;
Tamara Breus, Space Research Institute, Moscow, Russia;
Paul Cloutier, Rice University, Houston, USA;
Jack Connerney, Goddard Space Flight Center/NASA, Greenbelt, USA;
Tom Cravens, University of Kansas, Lawrence, USA;
Dana Crider, Goddard Space Flight Center/NASA, Greenbelt, USA;
Magda Delva, Österr. Akademie der Wissenschaften, Graz, Austria;
Eduard Dubinin, Max Planck Institut, Lindau, Germany;
Mats Holmstrom, Swedish Institute of Space Physics, Kiruna, Sweden;
Galina A. Kotova, Space Research Institute, Moscow, Russia;
Esa Kallio, Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland;
Alexander M. Krymskii, Rostov State University, Rostov-on-Don, Russia;
Robert Lin, University of California, Berkeley, USA;
Kiyoshi Maezawa, Institute of Space and Astronautical Science, Tokyo, Japan;
Christian Mazelle, Centre d'Etude Spatiale des Rayonnements/CNRS, Toulouse, France;
David Mitchell, University of California, Berkeley, USA;
Diedrich Möhlmann, Deutsches Zentrum für Luft- und Raumfahrt, Cologne, Germany;
Andy Nagy, University of Michigan, Ann Arbor, USA;
Norman Ness, Bartol Research Institute,  Newark, USA;
Erling Nielsen, Max Planck Institut, Lindau, Germany;
Marit Oieroset, University of California, Berkeley, USA;
Henri Reme, Centre d'Etude Spatiale des Rayonnements/CNRS, Toulouse, France;
Konrad Sauer, Max Planck Institut, Lindau, Germany;
Gerald Schubert, University of California, Los Angeles, USA;
Konrad Schwingenschuh, Österr. Akademie der Wissenschaften, Graz, Austria;
Jim Slavin, Goddard Space Flight Center/NASA, Greenbelt, USA;
Tilman Spohn,  Westfälische Wilhelms-Universität, Münster, Germany;
Jean-Gabriel Trotignon, LPCE/CNRS, Orleans, France;
Misha I. Verigin, Space Research Institute, Moscow, Russia;
Didier Vignes, Goddard Space Flight Center/NASA, Greenbelt, USA;
Daniel Winterhalter, Jet Propulsion Laboratory/Caltech, Pasadena, USA;
Alexander Zakharov, Space Research Institute, Moscow, Russia;