Abstract

In October 2011, ESA announced the selection of Solar Orbiter as one of the Cosmic Vision M missions, with the launch envisioned for 2017. If the implementation of Solar Orbiter proceeds as planned, we might have again in 2020, 40 years
after the pioneering Helios mission, a spacecraft which will determine in-situ the properties and dynamics of plasma, fields and particles in the inner (as close as 0.3 AU from the Sun) heliosphere, and as well survey the details of the Sun’s magnetised atmosphere with sophisticated remote sensing instruments. While Solar Orbiter has the potential to initiate a big step in our understanding of the above science issues, we have to realize that due to the somewhat different design of the mission compared to Helios (three-axis stabilized spacecraft, larger weight on remote sensing instruments) it might not surpass the results of Helios in every respect. It seems therefore worthwhile also to revisit some of the outcome from Helios light of better theoretical understanding and advanced analysis and modelling techniques developed during the past 20 years. This International Team project intends to reach an assessment of the progress in the fields of dynamic processes in the solar wind plasma, and the interaction of energetic particles with shocks/CMEs which was obtained from the evaluation of 1975 – 1983 Helios. The goal is to bring together scientists who are still familiar with the analysis of Helios data and the subtleties of the corresponding instruments, those who have in the past decade contributed to advances in the theoretical understanding and modeling techniques of heliopheric processes which were not available in the Helios era, and those who are now working on instrumentation for future missions which will explore the inner Heliosphere. As several of the envisioned Team members are co-investigators of particle and plasma instruments for the ESA/NASA Solar Orbiter mission, the outcome of the Team effort could result in valuable input to the planning of science objectives of that mission and allow a fine-tuning of some instrument capabilities. We plan to take a second look at the evaluation of multipoint observations from IMP8, ISEE-3, the Solar Maximum Mission (SMM), and will also explore possibilities to organize similar observations from particle and plasma instruments on current (STEREOA/ B, Wind, ACE, MESSENGER) and future (Solar Orbiter, BepiColombo, Solar Probe Plus, and possibly Interheliozond/Russia) missions in the inner Heliosphere.