The spacecraft -- a National Aeronautics and Space Administration-European Space Agency mission -- shows the sun has reduced its output of solar wind to a level that might reduce the natural shielding that envelops our solar system.
"The sun's million mile-per-hour solar wind inflates a protective bubble, or heliosphere, around the solar system," said Dave McComas, Ulysses' solar wind instrument principal investigator. Solar wind plasma -- a stream of charged particles ejected from the sun -- interacts with every planet in our solar system. It also defines the border between our solar system and interstellar space called the heliopause.
"With the solar wind at an all-time low, there is an excellent chance the heliosphere will diminish in size and strength," said Ed Smith, NASA's Ulysses project scientist at the Jet Propulsion Laboratory in Pasadena, Calif. "If that occurs, more galactic cosmic rays will make it into the inner part of our solar system."
Ulysses was carried into Earth orbit aboard space shuttle Discovery on Oct. 6, 1990.