ESA Science & Technology11-Jul-2005 10:12:37


Energetic particles

The magnetic explosion during a solar flare accelerates electrons and atomic nuclei to significant fractions of the speed of light. 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. When they hit SOHO, they appear as 'snow' in imaging instruments.


SOHO has two sets of telescopes for gauging the energetic particles:

  • COSTEP (Comprehensive Suprathermal and Energetic Particle Analyzer)
  • ERNE (Energetic and Relativistic Nuclei and Electron Experiment)

Both COSTEP and ERNE provide complementary detectors for various types of particles and energy bands, all angled to look along the magnetic field line that guides the particles. ERNE's detectors work at the higher energies.

3-D graph of galactic cosmic radiation identified by ERNE's high energy detector

Q & A on energetic particles

Which eruptions on the Sun produce energetic particles?

Some do, some don't. SOHO'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.

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