Meeting concludes on launch anniversary
6 October 2000On 6 October 1990, the Ulysses spacecraft was launched. Today, ten years later, the international band of scientists attending the 34th ESLAB symposium are concluding proceedings with their sense of excitement and eager anticipation undimmed. The meeting has heard of numerous observations, made over recent months, that are leading to new insights about the behaviour of the Sun and the heliosphere at solar maximum. Many speakers have looked forward to further observations over the next four years as the solar cycle returns to minimum.
Ulysses continues to return results not just about the heliosphere, but also about the solar system's interstellar environment. This morning, for example, Bruce McKibben from the University of Chicago, revealed how the COSPIN high energy telescope on Ulysses found that the composition of cosmic rays originating elsewhere in the galaxy matches the composition of the building blocks of the solar system. This is a surprise: galactic cosmic rays are much younger than the solar system, which has undergone more evolution.
The Ulysses mission so far has revealed just how complex the heliosphere is, in particular the variety of sources of energetic particles within it. "We always used to think of the Sun as the only source of particles in the heliosphere. Then we found interstellar particles, and now it turns out that interplanetary dust is a source of particles, too," said Richard Marsden, Ulysses project scientist.
Ulysses had a chequered start to its career, having been modified and then delayed for many years. Peter Wenzel, Head of Solar System Division at ESTEC, however, remarked that this was fortuitous. "If Ulysses had set off on schedule, its first orbit would have occurred at solar maximum, which is a complex time. We were lucky enough to encounter solar minimum first, which enabled us to establish a basic understanding of the Sun, from which we are far better equipped to make sense of the turmoil at maximum."