IMPACT: Science Goals and Firsts with STEREO

STEREO's IMPACT (In-situ Measurements of Particles and CME Transients) investigation provides the first opportunity for long duration, detailed observations of 1 AU magnetic field structures, plasma and suprathermal electrons, and energetic particles at points bracketing Earth's heliospheric location. The PLASTIC instrument, described in a companion presentation, will make plasma ion composition measurements completing STEREO's comprehensive in-situ perspective. Stereoscopic/3D information from the STEREO SECCHI imagers and SWAVES radio experiment, also described in this session, will make it possible to use both multipoint and quadrature studies to connect interplanetary Coronal Mass Ejections (ICME) and solar wind structures to CMEs and coronal holes observed at the Sun. IMPACT is also expected to test the patterns of solar energetic particle (SEP) events inferred from earlier statistical studies and multipoint measurements, and to resolve outstanding questions of source location(s) and seed populations with combinations of SEP composition measurements and other IMPACT and STEREO observations. Additional important insight will result from ongoing L1 viewpoint imaging and in-situ measurements from SOHO, WIND and ACE. In the late 1970s and early 1980s the Helios twin spacecraft mission obtained paired plasma, field and SEP in-situ data sets complemented by the Solwind and Solar Maximum Mission (SMM) coronagraph images of CMEs, and near-Earth in-situ data from IMP-8 and ISEE-3. IMPACT's updated instruments and modern data processing, transmitting, and analysis capabilities, with support from the other STEREO investigations and today's realistic 3D models of the corona, solar wind and CMEs, will prove or in some cases revolutionize the observational paradigms gleaned in the era of the Helios/Solwind/SMM/IMP-8/ISEE3 spacecraft combinations. The resulting views of in-situ space weather will without doubt leave us with a forever transformed perspective of L1 measurements and notions of what to expect from a CME.