WE ARE in the midst of an onslaught from outer space. The amount of stardust penetrating our solar system has tripled in the last few years, and it is expected to continue rising.
Most of the dust in the solar system originated here, and is concentrated in the same plane as the planets鈥� orbits, called the ecliptic. But until now researchers knew little about the dust arriving from other stars. Ulysses, a satellite jointly owned by the European Space Agency and NASA, is the first craft to measure dust outside the ecliptic, flying on an oblique orbit that takes it high above the sun鈥檚 poles and out as far as Jupiter.
Marcus Landgraf from the European Space Operations Centre in Darmstadt, Germany, has now analysed Ulysses data from 2000 to 2002 and compared it to data going back to 1992. He has found stardust is on the increase, and the rise coincides with changes in the sun鈥檚 activity. From 2000 to 2002, a period around the most recent solar maximum, more than three times as much stardust travelled through the solar system as during the preceding three years, when the sun鈥檚 activity was far lower.
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Landgraf believes this variation is due to the way the sun鈥檚 changing magnetic field interacts with the charged dust particles. At solar maximum, the sun鈥檚 magnetic field switches polarity, leaving a jumble of magnetic field lines with no particular direction. 鈥淟ike a spaceship that drops its shield, the sun drops its magnetic barrier, leaving the stardust to flow through the solar system unimpeded,鈥� says Landgraf.
But at solar minimum, when the sun has well-defined magnetic poles, its field focuses the stardust. During the most recent minimum, in 1995, the dust was deflected out of the solar system. But by the next minimum in 2006, the poles will have switched and Landgraf expects the particles to be focused into the solar system, causing the stardust to rain down even thicker (Journal of Geophysical Research, in press).
Levels of stardust are low compared to interplanetary dust. But Landgraf thinks the interaction between the two will have a big effect on Earth. 鈥淚nterstellar dust grains, which travel very fast, shatter interplanetary grains creating more, smaller grains,鈥� he says. So more dust could be entering Earth鈥檚 atmosphere.