What surprised Landgraf and his colleagues at the Max Planck Institute for Nuclear Physics in Heidelberg is that the influx of dust has continued to increase since activity on the sun calmed following the 2001 solar maximum.
The scientists believe the continued influx is due to the way in which the polarity changed. Instead of reversing completely, flipping north to south, the sun's magnetic poles have only rotated halfway and are now more or less lying sideways along the sun's equator.
"Before the current solar maximum, the grains were deflected out of the vicinity of the sun. Now with a global solar magnetic field weakened during maximum conditions, we see more grains," said Landgraf.
This weaker configuration of the magnetic field is allowing two to three times more stardust to enter the solar system than at the end of the 1990s. This influx of stardust could continue to increase as the field further weakens until the end of the current solar cycle in 2012.
Independent of the variations in the solar magnetic field, astronomers expect the influx of interstellar dust to increase sometime in the next 10,000 years when the solar system drifts into a galactic cloud known as the G-cloud.
Measurements of the G-cloud indicate it is full of gas. "And where there's more gas in the galaxy, there's more dust, normally," said Landgraf.
Brownlee, the University of Washington astronomer, serves as the principal investigator for NASA's Stardust spacecraft. Stardust was launched in 1999 to collect bits of interstellar dust and comet fragments and return them to Earth for analysis. Brownlee said the discovery of increased interstellar particles makes his job easier.
"In terms of Stardust collecting interstellar grains as part of its cruise, it makes us happier that the flux has increased recently and the particle sizes are bigger than estimated earlier," he said.
Stardust will deploy material called "aerogel" to capture the particles, which move at about 16 miles (26 kilometers) per second relative to the sun. When the particles hit the aerogela block of silicon-based substance that is 99.8 percent airthey slow down as they penetrate the material, creating carrot-shaped tracks.
A paper by Landgraf and colleagues on the influx of interstellar dust will appear in the October 2003 issue of the Journal of Geophysical Research.
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