Energetic particles from the Sun pose a threat to astronauts and satellites, and even to computers on the ground. Unlike much slower atomic particles in the solar wind, which travel straight out from the Sun, the energetic particles follow curved lines of the Sun's interplanetary magnetic field. The particles slant in towards the Earth from the west at about 45 degrees to the direction of the Sun.

Q & A on energetic particles

Which eruptions on the Sun produce energetic particles?

Some do, some don't. Cluster's great advantage in seeking an explanation is that bursts of particles can be directly related to events in the solar atmosphere seen by other instruments on the same spacecraft. The scientists hope to find ways of predicting the particle bursts.

What do the particles reveal about their origins?

By analysing the chemical elements present among the energetic particles, and their state of electric charge, scientists can learn about the circumstances of their acceleration. Some of the energetic particles don't even come from the Sun, but are 'anomalous cosmic rays' accelerated far out in space by shock waves in the solar wind.