Astronomers Get The First Detailed Look At The Space Between The Earth And The Sun

The two spacecraft that make up the NASA STEREO mission were launched last October. One probe is now travelling in an orbit ahead of the Earth while the other lags behind. Together the probes are imaging the Sun in 3D. They also have a unique perspective - they can view the space between the Sun and the Earth (the so-called Earth-Sun line), giving scientists their first views of this region of space.

The Rutherford Appleton Laboratory (RAL) in Oxfordshire and the University of Birmingham led an international effort to develop two identical Heliospheric Imager (HI) instruments. One HI is mounted on each of the two spacecraft so astronomers can watch the Earth-Sun line. In particular, this view gives scientists a ringside seat when giant clouds of material (Coronal Mass Ejections or CMEs) travel from the Sun to the Earth.

CMEs can be made up of more than 1000 million tonnes of charged particles and travel at up to 1000 km per second. When a CME reaches the Earth it can have dramatic effects; compressing the terrestrial magnetic field, generating displays of the northern lights, disrupting radio communications, overloading power grids and damaging satellites.

The ability to track CMEs as they leave the Sun, to understand how they propagate and evolve and to predict their arrival at Earth are all goals of the unique HI system. As the STEREO spacecraft move into their orbits over the coming months we will see increasingly better views of the 3D Sun and the passage of Earth-directed clouds in space. However, the UK HI instruments have now made their first observations of CMEs in the inner solar system, showing spectacular images of these clouds and demonstrating that the instruments are operating flawlessly.

At the RAS National Astronomy Meeting in Preston, Professor Richard Harrison and Dr Chris Davis of the Rutherford Appleton Laboratory presented spectacular images and movies of these dramatic events taken by UK cameras mounted on the two STEREO spacecraft.

Images and animations are available at http://www.stereo.rl.ac.uk/STEREO_Gallery.html