Solar physics in STEREO

Abstract

The twin spacecraft of the NASA STEREO mission were launched successfully on 26 October 2006 and are now in heliospheric orbit with all instruments operating well. The mission was designed to make observations of the Sun from two distinct viewing directions in order to provide 3-D information about structures in the solar chromosphere and corona. These unprecedented measurements will help solar scientists to understand the complex interactions between plasma and magnetic fields which result in sudden dramatic eruptions known as coronal mass ejections (CMEs). In order to achieve the required separation, the two spacecraft used lunar fly-bys to inject them into heliospheric orbits at distances of approximately 1 AU from the Sun, one travelling ahead of the Earth and the other lagging behind. The two spacecraft (accordingly named Ahead and Behind, “A” and “B”) will continue to move away from the Earth at around half a million miles per year (as the Earth–Sun–spacecraft angle increases by 22.5° per year). Each spacecraft carries seven instruments (figure 1). Four of these form SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation): an extreme ultraviolet imager (EUVI); two white-light coronagraphs (COR-1 and COR-2); and a heliospheric imager (HI). These instruments will study the 3-D evolution of CMEs from birth at the Sun’s surface through the corona and interplanetary medium to its eventual impact at Earth. As well as SECCHI there are instruments to make in situ measurements: PLASTIC (PLAsma and SupraThermal Ion Composition), which IMPACT (deployed boom)