NASA’s Juno spacecraft enters Jupiter’s magnetic field

Nearly five years ago, NASA’s Juno spacecraft left Earth headed for Jupiter. This week, it reached one of its first scientific milestones — entering the gas giant’s magnetosphere, or magnetic field.

“We’ve just crossed the boundary into Jupiter’s home turf,” Scott Bolton, the mission’s principal investigator and a scientist at the Southwest Research Institute, confirmed in a news release. “We’re closing in fast on the planet itself and already gaining valuable data.”

The probe’s official rendezvous with Jupiter will happen on Monday, July 4.

In the meantime, Juno and its instruments will continue to collect data about the nature of Jupiter’s upper atmosphere. The spacecraft was able to collect valuable information as it transitioned from interplanetary space into Jupiter’s magnetosphere, passing the bow shock created as fast-moving solar winds and high-energy solar particles slam into the planet’s magnetic field.

Outside the sun, Jupiter’s magnetic field is the largest obstacle 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,” said William Kurth, a planetary scientist at the University of Iowa. “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.”

Kurth is co-investigator of the Waves investigation, an effort to better understand Jupiter’s auroral region and the interactions between the magnetosphere’s particles and solar winds.

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Though it’s early in Juno’s scientific mission, its instruments are already picking up on unexpected patterns. Unusual signatures before and after crossing the boundary between space and magnetosphere suggest the transition is even more complex than scientists thought.

“This unusual boundary structure will itself be the subject of scientific investigation,” explained Barry Mauk, a researcher at Johns Hopkins University Applied Physics Laboratory and head of Juno’s JEDI mission.

Once in orbit around Jupiter, Juno will spent a year studying the composition of the planet’s core, surface and atmosphere.