NASA's Juno spacecraft enters Jupiter's magnetic field

Washington: The Juno spacecraft, which is on course to swing into orbit around Jupiter on Monday (July 4), has entered the planet's magnetosphere, NASA said.

"We've just crossed the boundary into Jupiter's home turf," said Juno Principal Investigator Scott Bolton of Southwest Research Institute, San Antonio. "We're closing in fast on the planet itself and already gaining valuable data."

Science instruments on board detected changes in the particles and fields around the spacecraft as it passed from an environment dominated by the interplanetary solar wind into Jupiter's magnetosphere.

On June 24, the spacecraft passed through the bow shock just outside the planet's magnetosphere - where the movement of particles in space is controlled by what's going on inside Jupiter.

Data from Juno's Waves investigation, presented as audio stream and color animation, as the spacecraft entered the planet's realm on June 24 and the transit into the lower density of the Jovian magnetosphere on June 25.

"The bow shock is analogous to a sonic boom," said William Kurth of the University of Iowa in Iowa City, lead co-investigator for the Waves investigation. "The solar wind blows past all the planets at a speed of about a million miles per hour, and where it hits an obstacle, there's all this turbulence."

The obstacle is Jupiter's magnetosphere, which is the largest structure in the solar system.

"If Jupiter's magnetosphere glowed in visible light, it would be twice the size of the full moon as seen from Earth," Kurth said. And that's the shorter dimension of the teardrop-shaped structure; the dimension extending outward behind Jupiter has a length about five times the distance between Earth and the sun.

While this transition from the solar wind into the magnetosphere was predicted to occur at some point in time, the structure of the boundary between those two regions proved to be unexpectedly complex, with different instruments reporting unusual signatures both before and after the nominal crossing.

The Juno spacecraft launched on August 5, 2011, from Cape Canaveral, Florida, will help solve the mysteries of Jupiter by looking at its interior.