The main activity in the field of near-Earth space plasma physics is the CLUSTER mission. This mission comprises, together with SOHO, the first "cornerstones" of ESA's scientific program 'Horizon 2000'. The prime purpose of CLUSTER is the identification and detailed study of the space-time structure of the processes at plasma boundaries in the Earth's magnetosphere. The four CLUSTERspacecraft with identical instrumentation fly in a variable tetrahedral formation when crossing regions of interest. This enables scientists for the first time to study three-dimensional and time-varying phenomena and makes it possible to distinguish between spatial and temporal variations.
After the loss of the CLUSTER mission due to the launch failure of the first Ariane 5 rocket on June 6, 1996, Cluster was repeated with 2 launches with Sojuz rockets in July and August 2000. The science phase began on 1. February 2001 and is presently planned to continue until the end of 2005.
MPE participates significantly in 2 of the 11 experiments onboard each spacecraft: the EDI (Electron Drift Instrument) for the measurement of electric fields, and the CIS (Cluster Ion Spectrometer) experiment for the determination of the 3D distribution function of ions in the energy range ~5 eV/e to 40 keV/e. CIS also provides mass/charge resolution and allows to determine the 3D distribution function of the most abundant ions in the near-Earth environment (H+, H2+, He+, O+).
The Sun and Heliosphere
In the field of solar and heliospheric physics we investigate active regions on the sun, and acceleration processes on the sun and in interplanetary space, for example at shock waves caused by coronal mass ejections. The in-situ measurements with the experiments CELIAS (Charge, Element, and Isotope Analysis System) onboard SOHO (Solar and Heliospheric Observatory) and SEPICA (Solar Energetic Particle Ionic Charge Analyzer) onboard ACE (Advanced Composition Explorer) provide direct measurements of isotopic, elemental, and ionic charge composition of the solar wind and suprathermal particles. These measurements provide insight into the location of the acceleration region and into fractionation and acceleration processes. Results from the SAMPEX (Solar, Anomalous and Magnetospheric Particle Explorer) satellite in a low altitude polar orbit provided during the last years important measurements of the ionic charge of Anomalous Cosmic Rays (ACR), using the Earth's magnetic field for the determination of the ionic charge of the ions. The same technique enabled us also to determine for the first time the ionic charge of particles of solar origin over the extended energy range ~ 0.5 - 70 MeV/nucleon.
Interplanetary and interstellar Dust, Comets
Outside of plasma physics studies of interstellar and cometary dust are planned for the STARDUST and ROSETTA missions. Stardust was launched on February 2, 1997 and has already provided first results. Because of problems with the Ariane 5 launcher Rosetta has been delayed and was finally successfully launched in March 2004. All activities in this field of research have been transferred during 2003 to the Max-Planck-Institute for Solar System Research ( MPS) and will be continued there in the group "Planets, Comets, Small Bodies in the Solar System".