Controllers at the Jet Propulsion Laboratory have commanded one of NASA's daring Voyager probes to spin around this week in a bid to detect a bend in the solar wind at the edge of the solar system, the agency announced Tuesday.

Artist's concept of Voyager. Credit: NASA
 
More than three decades since launching from Earth, NASA's Voyager probes continue beaming back scientific data from the unexplored frontier of the solar system.

Flying nearly 11 billion miles from Earth, the Voyager 1 spacecraft is surveying one of the least-known reaches of the solar system -- the region where the sun's influence wanes and interstellar space begins.

Voyager 1's low energy charged particle instrument registered a strange reading last June indicating the speed of the solar wind had dropped to zero. The solar wind, a flow of charged particles, normally streams away from the sun at a million miles per hour.

Scientists know such a measurement is misleading. The solar wind curves in the heliosheath, the outer edge of the solar system where Voyager 1 is now exploring. Inside the heliosheath, the solar wind is slowed by the pressure of interstellar gas.

The heliosphere, the area of the sun's influence, is shaped like a bubble in the sun's direction of travel and stretches out like a tail behind.

"Because the direction of the solar wind has changed and its radial speed has dropped to zero, we have to change the orientation of Voyager 1 so the low energy charged particle instrument can act like a kind of weather vane to see which way the wind is now blowing," said Edward Stone, Voyager's project manager at the California Institute of Technology.

The nuclear-powered spacecraft rolled 70 degrees counterclockwise Monday and held that position for more than two-and-a-half hours with its rapidly spinning gyrocopes, according to a JPL press release.

It was the second such roll-and-hold maneuver for Voyager since 1990.

According to JPL, five more such spins are planned over the next seven days to point Voyager 1's charged particle sensor in different directions. Researchers hope to catch a whiff of the solar wind and gauge which way it is turning, but it could be months before results are released.

It takes 16 hours just for Voyager 1's radio signals to reach Earth.

A sketch of the heliosphere and its boundary with interstellar space. Credit: NASA
 
"Knowing the strength and direction of the wind is critical to understanding the shape of our solar bubble and estimating how much farther it is to the edge of interstellar space," Stone said.

More weekly rolls are on tap over the next three months, according to NASA.

"We do whatever we can to make sure the scientists get exactly the kinds of data they need, because only the Voyager spacecraft are still active in this exotic region of space," said Jefferson Hall, Voyager mission operations manager at JPL. "We were delighted to see Voyager still has the capability to acquire unique science data in an area that won't likely be traveled by other spacecraft for decades to come."

Voyager 1 left Earth in September 1977 and flew by Jupiter and Saturn in 1979 and 1980. An identical craft named Voyager 2 also made flyby visits to Uranus and Neptune.

Both spacecraft could pass the heliopause, the border with interstellar space, later this decade. Scientists don't know when the Voyager craft will reach interstellar space, but data from the ongoing roll maneuvers could help researchers make an estimate.