Stephen Withers
Wednesday, 24 September 2008 09:46
Science -
Space
Page 1 of 2
The solar wind emanating from the Sun has fallen to the lowest level observed since accurate readings have been made.
The solar wind is the stream of charged particles emitted by the Sun. It provides a natural barrier around the solar system that keeps out the wind from other stars and blocks many of the cosmic rays (actually particles) originating from other parts of the Milky Way.
And that's why the drop in the solar wind detected by the joint ESA/MASA Ulysses mission is significant.
Compared with previous Ulysses measurements, the strength of the solar wind has decreased by 20 percent. The wind strength is known to vary with solar activity, but the current low has lasted longer than expected
"With the solar wind at an all-time low, there is an excellent chance that the heliosphere will diminish in size and strength," said Ed Smith, NASA's Ulysses project scientist at the Jet Propulsion Laboratory. If that occurs, more galactic cosmic rays will make it into the inner part of our Solar System."
(The heliosphere is the region of space surrounding the solar system that is subject to the solar wind.)
While cosmic rays have little direct impact on the Earth thanks to its magnetic field, they are a significant factor for space travel. The electronics used on unmanned interplanetary spacecraft must be able to resist their impact, and astronauts face health risks (notably an increased risk of cancer) from exposure to cosmic rays if they go beyond low Earth orbit.
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