One of the most important scientific advances of the space age was the discovery of Coronal Mass Ejections (CMEs). Travelling outward from the Sun at speeds up to 2000 km/s, CMEs appear as an important factor of the space-weather, which has multiple geospheric, biospheric and technological effects. Despite the importance of CMEs, there are still many open questions concerning their origin, evolution, structure or extent in the interplanetary space.

Further progress in understanding of fundamental nature and origin of CMEs requires detailed data on their 3-D structure. To perform this task the STEREO (Solar TErrestrial RElations Observatory) mission, consisting of two identical spacecraft, is launched on 25 October 2006. To provide the images for a stereo reconstruction of solar eruptions, one spacecraft (STEREO A) will lead Earth in its orbit and another (STEREO B) will be lagging. Both spacecraft will carry a similar cluster of telescopes and in-situ measurement equipment.

The STEREO science objectives are to:

• understand the origin and consequences of CMEs
• determine the processes that control CME evolution in the heliosphere and their interaction with the Earth's magnetosphere by tracking the CME-driven disturbances from the Sun to Earth's orbit
• discover the mechanisms and sites of solar energetic particle acceleration
• determine the 3D structure and dynamics of coronal and interplanetary plasmas and magnetic fields
• probe the solar dynamo through its effects on the corona and heliosphere, and provide early warnings of solar eruptions.

 

Each STEREO spacecraft carries two instruments:

• STEREO/WAVES (SWAVES) - an interplanetary radio burst tracker that traces the generation and evolution of travelling radio disturbances from the Sun to the orbit of Earth.
• PLAsma and Supra Thermal Ion and Composition (PLASTIC) - samples the solar wind and suprathermal particles, providing measurements of kinetic properties and composition.

 

and two instrument suites:

• Sun Earth Connection Coronal and Heliospheric Investigation (SECCHI) - consists of 5 telescopes that observe the solar corona and inner heliosphere from the surface of the Sun to the orbit of the Earth.
• In-situ Measurements of Particles and CME Transients (IMPACT) - provides 3D distribution and plasma characteristics of solar energetic particles and the local vector magnetic field.

 

IWF is participating in the SWAVES scientific team.

 

Further information on STEREO is found at NASA.