From: baalke@zagami.jpl.nasa.gov   
      
   European Space Agency   
   Science News Release SNR 13-2003   
   Paris, France			   
   18 August 2003   
      
   ESA sees stardust storms heading for Solar System   
      
   Until ten years ago, most astronomers did not believe stardust could enter our   
   Solar System. Then ESA's Ulysses spaceprobe discovered minute stardust   
   particles   
   leaking through the Sun's magnetic shield, into the realm of Earth and the   
   other   
   planets. Now, the same spaceprobe has shown that a flood of dusty particles is   
   heading our way.   
      
   Since its launch in 1990, Ulysses has constantly monitored how much stardust   
   enters the Solar System from the interstellar space around it. Using an   
   on-board   
   instrument called DUST, scientists have discovered that stardust can actually   
   approach the Earth and other planets, but its flow is governed by the Sun's   
   magnetic field, which behaves as a powerful gate-keeper bouncing most of it   
   back. However, during solar maximum -- a phase of intense activity inside the   
   Sun that marks the end of each 11-year solar cycle -- the magnetic field   
   becomes   
   disordered as its polarity reverses. As a result, the Sun's shielding power   
   weakens and more stardust can sneak in.   
      
   What is surprising in this new Ulysses discovery is that the amount of stardust   
   has continued to increase even after the solar activity calmed down and the   
   magnetic field resumed its ordered shape in 2001.   
      
   Scientists believe that this is due to the way in which the polarity changed   
   during solar maximum. Instead of reversing completely, flipping north to south,   
   the Sun's magnetic poles have only rotated at halfway and are now more or less   
   lying sideways along the Sun's equator. This weaker configuration of the   
   magnetic shield is letting in two to three times more stardust than at the end   
   of the 1990s. Moreover, this influx could increase by as much as ten times   
   until   
   the end of the current solar cycle in 2012.   
      
   The stardust itself is very fine -- just one-hundredth of the width of a human   
   hair. It is unlikely to have much effect on the planets but it is bound to   
   collide with asteroids, chipping off larger dust particles, again increasing   
   the   
   amount of dust in the inner Solar System. On the one hand, this means that the   
   solar panels of spacecraft may be struck more frequently by dust, eventually   
   causing a gradual loss of power, and that space observatories looking in the   
   plane of the planets may have to cope with the haze of more sunlight diffused   
   by   
   the dust.   
      
   On the other hand, this astronomical occurrence could offer a powerful new way   
   to look at the icy comets in the Kuiper Belt region of the outer Solar System.   
   Stardust colliding with them will chip off fragments that can be studied   
   collectively with ESA's forthcoming infrared space telescope, Herschel. This   
   might provide vital insight into a poorly understood region of the Solar   
   System,   
   where the debris from the formation of the planets has accumulated.   
      
   Back down on Earth, everyone may notice an increase in the number of sporadic   
   meteors that fall from the sky every night. These meteors, however, will be   
   rather faint.   
      
   Astronomers still do not know whether the current stardust influx, apart from   
   being favoured by the particular configuration of the Sun's magnetic field, is   
   also enhanced by the thickness of the interstellar clouds into which the Solar   
   System is moving. Currently located at the edge of what astronomers call the   
   local interstellar cloud, our Sun is about to join our closest stellar   
   neighbour   
   Alpha Centauri in its cloud, which is less hot but denser.   
      
   ESA's Ulysses data make it finally possible to study how stardust is   
   distributed   
   along the path of the Solar System through the local galactic environment.   
   However, as it takes over 70 thousand years to traverse a typical galactic   
   cloud, no abrupt changes are expected in the short term.   
      
   Notes to editors   
      
   The results of this investigation will appear in the October 2003 issue of   
   Journal of Geophysical Research. The investigation has been conducted by a team   
   lead by Markus Landgraf of ESA's European Space Operation Centre in Darmstadt   
   (Germany) and including Harald Krüger, Nicolas Altobelli, and Eberhard Grün of   
   the Max Planck Institute for Nuclear Physics in Heidelberg (Germany).   
      
   Ulysses is the first mission to study the environment of space above and below   
   the Sun's poles. It is a joint mission with NASA and has been in space since   
   1990, after a mission extension agreed in 2000. Launched from the Space Shuttle   
   Discovery in October 1990, Ulysses has now completed two orbits, passing both   
   the Sun's north and south pole on each occasion. Its data gave scientists their   
   first look at the variable effect that the Sun has on the space that surrounds   
   it.   
      
   The Ulysses DUST experiment provides direct observations of dust grains   
   weighing   
   less than a millionth of a gram in interplanetary space as Ulysses moves along   
   an orbit that takes it periodically away from the Sun and from the plane of the   
   planets -- a disc known as the ecliptic. DUST measures the mass, speed, flight   
   direction, and electric charge of individual dust particles.   
      
   Astronomers wanted to know what portion of dust is provided by comets and   
   asteroids and what, instead, comes directly from interstellar space. By taking   
   measurements when Ulysses was farthest from the Sun and high above the   
   ecliptic,   
   in regions where cometary dust can hardly reach, scientists were able to detect   
   and isolate particles of stardust entering the Solar System from the outer   
   space. To confirm that these dust grains are indeed of interstellar origin,   
   Landgraf and his collaborators verified that the dust had the same flight   
   direction and speed as the atoms of helium which are known to come exclusively   
   from interstellar space.   
      
   For further information, please contact:   
      
   Markus Landgraf, Mission Analyst   
   ESA - ESOC (European Space Operations Centre, Germany)   
   Tel: + 49 6151 90 3627   
   Fax: + 49 6151 90 2625   
   E-mail: markus.landgraf@esa.int   
      
   ESA Science Programme Communication Service   
   Tel: + 31 71 565 3273   
   Fax: + 31 71 565 4101   
      
   ESA Media Relations Service   
   Tel: + 33 1 5369 7155   
   Fax: + 33 1 5369 7690   
      
   IMAGE CAPTIONS:   
      
   [Image 1:   
   http://www.esa.int/export/esaCP/SEMDU4ZO4HD_index_1.html]   
   SOHO image of the Sun. SOHO is a project of international cooperation between   
   ESA and NASA. SOHO's EIT (Extreme ultraviolet Imaging Telescope) images the   
   solar atmosphere at several wavelengths and, therefore, shows solar material at   
   different temperatures. In the images taken at 304 Angstroms, the bright   
   material is at 60 000 to 80 000K. In those taken at 171, at 1 million Kelvin.   
   195 Angstrom images correspond to about 1.5 million Kelvin. The hotter the   
      
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