Solar scientists converge as solar activity peaks
29 September 2000As the Ulysses spacecraft hurtles through space towards the Suns south pole, more than 100 scientists from 16 countries will be speeding their way through airspace next week towards ESTEC, ESAs technical centre near Amsterdam. They will converge to discuss the very latest results from the intrepid spacecraft.
Ulysses is about to pass over the Suns south pole, just as the 11 year cycle of solar activity peaks. During the spacecrafts previous south polar passage in 1994, solar activity was approaching a minimum. The scientists will be comparing observations taken then and now to see how changes in solar activity affect the heliosphere, the giant magnetic bubble blown out into space by the solar wind which engulfs all the planets.
During solar minimum, for example, Ulysses found a sharp boundary between relatively slow moving solar wind emanating from the Suns equatorial regions and fast wind emanating from the poles. Already during this latest polar pass, the spacecraft has found no such clear boundary: solar wind speeds are highly variable whatever the latitude. The meeting will discuss why this is should be so.
We already know that the Suns increased activity at solar maximum is a symptom of magnetic upheaval below the surface as the Suns magnetic field loses all polarity. This increased magnetic complexity leads to solar storms and coronal mass ejections, when the Sun spits out large volumes of coronal matter into the heliosphere. Once the maximum is over, polarity returns to the Sun, but in reverse. The south magnetic pole becomes the north and vice versa. The scientists will discuss how this tortuous process is reflected in the behaviour and structure of the heliosphere.
Another issue will be the fate of energetic particles and dust entering the heliosphere from elsewhere in the galaxy. At solar minimum, Ulysses found that the magnetic field carried by the solar wind was much more tangled than expected. This prevented cosmic rays entering the heliosphere from gaining easy access over the poles. What happens at solar maximum? Results presented from some of the Ulysses instruments will reveal the answer.
The scientists will be meeting at the 34 Eslab symposium on the '3D heliosphere at solar maximum' which also marks the 10th anniversary of Ulysses launch. The European spacecraft was sent on its journey to explore the region of space above the Suns poles by the Space Shuttle Discovery in October 1990. It completed its first solar polar orbit in 1998 and is expected continue observing until 2004.
Daily updates about the symposium results will be available on this website from 3 to 6 October.