ESA Science & Technology30-Jun-2005 16:42:11

Science Highlights from the Second Solar Orbit

Energetic Particles

One of the key discoveries made during the high-latitude passes at solar minimum was the unexpected ease with which energetic particles, accelerated at low-to-middle latitudes, were able to reach the polar regions of the heliosphere. This discovery prompted theorists to re-assess existing models of the heliospheric magnetic field, leading ultimately to new suggestions regarding the source of the solar wind itself. An obvious question when Ulysses returned to high latitudes at solar maximum was: do energetic particles have the same easy access when the heliosphere is much more chaotic? The observations provided an unequivocal answer: yes. The Ulysses data confirmed the presence of large fluxes of energetic particles over the poles, and revealed that the absolute intensity of these particles is comparable to that measured simultaneously in the ecliptic near 1 AU. This has lead to the idea of the inner heliosphere near solar maximum acting as a "reservoir" for solar energetic particles.

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