Just as solar storms are brewing, the European-built space probe, Ulysses, is venturing over the Sun's south pole for the second time in its 10 year life. The intrepid spacecraft will pass 70o south on 8 September, shortly before the Sun's 11 year activity cycle is due to peak. Solar storms are already numerous and the high latitude solar wind (the stream of charged particles blowing away from the Sun) is chaotic and blustery.
Conditions are very different from those Ulysses encountered during its first south polar pass in 1994 when solar activity, which is related to the magnetic behaviour of the Sun, was very low. Then, the solar wind at high latitudes was fast, but steady. This latest polar pass gives scientists the opportunity to learn just how different the polar regions of the Sun are at solar maximum compared with minimum.
After spending four months above 70o south, Ulysses will swing towards the equator early next year to turn its attention to the northern hemisphere, beginning its passage over the north pole on 3 September 2001. Although it will be travelling the same path it followed six years ago, conditions will be quite different and new discoveries are eagerly awaited.
Since launch in October 1990, Ulysses has already proved one of the most successful interplanetary missions ever. A joint ESA/NASA mission, it is the first spacecraft ever to be launched into an orbit outside the ecliptic, the plane in which the planets orbit the Sun. From this unique vantage point, it has changed our view of the heliosphere, the region of space filled by the solar wind and over which our Sun exerts its influence.
At solar minimum, instruments on board Ulysses found that the fast solar wind, emanating from the Sun's poles, blows at a steady 750 km/s and fills a large fraction of the heliosphere. The state-of-the-art instruments were also able to show that the boundary between the fast wind and the slower, more variable wind from the equatorial regions, is surprisingly sharp. Another surprise was that the effects of collisions, occurring at low latitudes between fast and slow wind streams, continue to be felt all the way up to the poles.
Ulysses discoveries, however, have not been confined to the Sun and heliosphere. Instruments on board the spacecraft also made the first ever measurements of dust particles and neutral helium atoms originating outside the solar system. These findings have contributed to a major increase in our knowledge about the gas and dust clouds surrounding the heliosphere. Other measurements have lead to a better understanding of processes occurring even further away, in distant supernova explosions.
During the relative simplicity of solar minimum, Ulysses made many surprise discoveries. During the relative chaos and unpredictability of solar maximum, many more are expected. Exciting times are ahead in our quest to understand the Sun and its heliosphere.
For more information, please contact :
ESA - Communication Department
Media Relations Office
Dr. Richard Marsden,
ESA - Ulysses Project Scientist
Tel: +31 71 565 3583
Further information on Ulysses can be found at http://sci.esa.int/ulysses.
Information on the ESA Science Programme can be found at: http://sci.esa.int . Further information on ESA at: http://www.esa.int