NASA's Jupiter-bound Juno spacecraft has entered the planet's magnetosphere, where the movement of particles in space is controlled by what's going on inside Jupiter. "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."

Juno is on course to swing into orbit around Jupiter on July 4. 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. Data from Juno's Waves investigation, presented as audio stream and color animation, indicate the spacecraft's crossing of the bow shock just outside the magnetosphere on June 24 and the transit into the lower density of the Jovian magnetosphere on July 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.

Out in the solar wind a few days ago, Juno was speeding through an environment that has about 16 particles per cubic inch (one per cubic centimeter). Once it crossed into the magnetosphere, the density was about a hundredfold less. The density is expected to climb again, inside the magnetosphere, as the spacecraft gets closer to Jupiter itself. The motions of these particles traveling under the control of Jupiter's magnetic field will be one type of evidence Juno examines for clues about Jupiter's deep interior.

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.

"This unusual boundary structure will itself be the subject of scientific investigation," said Barry Mauk of the Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, who is the instrument lead for the Jupiter Energetic-Particle Detector Instrument (JEDI) on Juno.

Juno Spacecraft Kicks into Planned Autopilot for July 4 Jupiter Burn
On Thursday mission controllers transmitted command product "ji4040" into deep space, to transition the solar-powered Juno spacecraft into autopilot. It took nearly 48 minutes for the signal to cover the 534-million-mile (860-million-kilometer) distance between the Deep Space Network Antenna in Goldstone, California, to the Juno spacecraft. While sequence ji4040 is only one of four command products sent up to the spacecraft that day, it holds a special place in the hearts of the Juno mission team.

"Ji4040 contains the command that starts the Jupiter Orbit insertion sequence," said Ed Hirst, mission manager of Juno from NASA's Jet Propulsion Laboratory in Pasadena, California. "As soon as it initiates - which should be in less than a second - Juno will send us data that the command sequence has started."

When the sequence kicked in, the spacecraft began running the software program tailored to carry the solar-powered, basketball court-sized spacecraft through the 35-minute burn that will place it in orbit around Jupiter.

"After the sequence executes, Juno is on autopilot," said Hirst. "But that doesn't mean we get to go home. We are monitoring the spacecraft's activities 24/7 and will do so until well after we are in orbit."

Also [today], NASA announced a collaboration with Apple that will serve to enhance the agency's efforts to inform and excite the public about dramatic missions of exploration like Juno. "Destination: Juno" is a synergy between two seemingly disparate worlds: popular music and interplanetary exploration. The works resulting from this collaboration showcase exploratory sounds from artists who have been inspired by Juno and other NASA missions, including Brad Paisley, Corinne Bailey Rae, GZA, Jim James featuring Lydia Tyrell, QUIN, Trent Reznor and Atticus Ross, Weezer and Zoe.

Apple has captured moments in this journey with a behind-the-scenes documentary spearheaded by the Juno mission's principal investigator, Scott Bolton, and scored by Academy Award winners Trent Reznor and Atticus Ross. The content is available on various Apple platforms. Other Juno-related content, including educational opportunities with Bill Nye on and an "Interactive Guide to NASA's Juno Mission," will roll out over the course of a year and throughout the length of the Juno mission.