Some of the most exciting observations to have arisen from the Galileo mission has resulted from the close flybys of the Galileo orbiter past the four Galilean moons. These observations have revealed the existence of an internal magnetic field at Ganymede and possibly also at Io. This is rather a surprise since it has long been assumed that small planetary bodies have cooled down sufficiently that internal dynamo processes were no longer an issue. Magnetometer measurements have also revealed that both Europa and Callisto have conducting interiors resulting in induced magnetic field signatures which can be used to aid interpretation of the internal structure of these moons.

While originally scheduled for launch in 1995 the Oersted satellite kept being postponed by delays at the US Air Force Argos satellite, the main mission of the planned Delta II launch. Then, after a record-setting series of 10 scrubbed count-downs, the Oersted satellite was finally launched on 23 February 1999. Successfully in orbit all instruments, basically, functioned well. However, the boom deployment gave problems, the attitude control was poor, the timing of some data sets was uncertain and important house-keeping data were missing. As a consequence the vectorial geomagnetic observations, Oersteds prime data, were patchy and poor. It took hard work through an extended commissioning phase of almost 6 month's duration to solve the problems. Satellite software was modified, parameters and procedures were changed, time stamping and other complicated issues were re-analyzed. And finally, like in a fairy tale with happy end, the satellite came to function properly and is now supplying a wealth of high-quality geomagnetic observations. The talk will present the background for the Oersted mission and outline its scientific goals. The instrumentation and orbit of the satellite will be briefly described. The actual status for the mission and the prospects of future operation will be reviewed. The geomagnetic data sets provided by the Oersted satellite has now been accepted by IAGA to form the basis for the IGRF2000 geomagnetic field model. This issue and other uses of the Oersted data for geomagnetic field modelling will be discussed. Further, the use of Oersteds high-precision magnetic measurements for exploring ionospheric and magnetospheric current systems will be reviewed. The emphasis will be on investigations of high-latitude field-aligned current systems and their relations to conditions in the solar wind and in the outer magnetosphere and their connection to ionospheric current systems.

Models of the Earth's main magnetic field have both academic and commercial applications and are derived from magnetic measurements on land, air and sea and by satellites in low Earth orbit. We discuss current techniques and data treatments that help isolate the core-generated component from the fields of other sources. We examine the legacy of Magsat, the last high quality satellite mission in 1979-1980, and present some recent models and results from the Oersted mission.

The heliospheric magnetic field is a consequence of the Sun's magnetic field being carried out into interplanetary space, frozen in to the solar wind. As such its large scale structure is related to the structure of the magnetic fields in the solar corona and to the dynamics of the outflowing solar wind. The greatest advance in our understanding in recent years has come from the Ulysses mission which is the first spacecraft to explore the heliosphere over the full range of solar latitudes away from the ecliptic plane. This talk will review the key results of the first Ulysses polar orbit of the Sun which has given us a clear picture of the 3D structure of the heliospheric field at solar minimum. Ulysses is now undergoing a second orbit at a time of high solar activity. The recent results so far will be contrasted with those obtained from the first orbit.

Lunar magnetic fields were discovered by the Apollo missions some 26 years ago and recently have been studied in detail by Lunar Prospector (LP) from a polar mapping orbit. The discovery within the last two years of strong remanent magnetization in the Martian crust by the Mars Global Surveyor (MGS) MAG/ER Experiment, has challenged our fundamental understanding of Mars' early history and thermal evolution. The lack of existence of a planetary dynamo coupled with the surprising correlation of crustal magnetic sources with the age of the terrain, provide a unique window into the thermal history of Mars and the dynamic evolution of the crust. Linear features with alternate polarity radial magnetization, extending more than 2000 Km, are found over a third of the southern hemisphere. Their interpretation in terms of Earth-like tectonic processes and equivalent crustal magnetization strength is not readily apparent and is largely an unsolved problem at the present time. At the Moon, the strongest magnetized regions are found over the antipodal regions to the Imbrium, Orientale, Serenitatis and Crisium impact basins. At Mars, the Hellas, Argyre and Isidis impact basins and the Tharsis volcanos do not exhibit detectable crustal magnetization. The MAG/ER results from the LP and MGS missions are providing exciting and new information about the dramatic role that giant impacts may have played in modifying the crustal magnetization of planetary objects in the early Solar System.

In much earlier work towards the interpretation of the irregular time series (including superchrons) of polarity reversals in terms of the magnetohydrodynamic "geodynamo" operating within the Earth's liquid metallic outer core, I invoked the influence of modest lateral variations in the physical conditions prevailing at the core-mantle boundary and their fluctuations on geological timescales, whose effects on core motions are greatly enhanced by the action of Coriolis forces due to the Earth's rotation. Here I discuss a further useful working hypothesis (R. Hide, Philos. Trans. Roy. Soc. A, March 2000), which invokes the additional recently-discovered process (see R. Hide, Nonlinear Processes in Geophysics, 4, 201-205 (1998)) of nonlinear quenching of fluctuations in self-exciting dynamos, which could also be tested when suitable numerical geodynamo models become available.

Direct observations of the magnetic field taken from the Earth's surface play a vital role in understanding the magnetic field generated in the fluid core. We present the latest images of the historical core field from 1590 onwards, derived primarily from observations made on commercial and naval ships, and discuss the latest contributions made by satellite missions such as Oersted.

The interplanetary magnetic field of the solar wind is recognised to be a fully-developed turbulent medium by, for example, the power law form of its power spectrum, and the self-affine behaviour of its structure functions. Here we show new evidence of its scale-free properties by the power law form of occurrence frequency distributions of burst sizes, durations, and inter-burst intervals of the Poynting flux. Similar burst distributions (as well as similar properties in the other scaling measures) have been reported both in the solar corona and in the earth s magnetosphere, to which the solar wind is coupled. In both these systems this scale-free aspect has been attributed to Self-Organized Criticality (SOC). This leads us to discuss two questions: First, what is the relationship of SOC to turbulence and the distinction between them? Second, is turbulence or SOC an internal property of the solar wind and magnetosphere or is it externally driven by a turbulent or SOC solar corona?