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Jupiter exploration

On the evening of July 4, Juno — a solar-powered spacecraft the size of a basketball court — will fire its main engine for 35 minutes, placing it into a polar orbit around the gas giant.

During the flybys, the spacecraft will probe beneath the obscuring cloud cover of the Solar System’s largest planet and study its auroras to learn more about the planet’s origins, structure, atmosphere and massive magnetosphere.

A series of 37 planned close approaches during the mission will eclipse the previous record for Jupiter set in 1974 by NASA’s Pioneer 11 spacecraft of 27,000 miles (43,000 km).

Juno obtained this color view on June 28, 2016, at a distance of 3.9 million miles (6.2 million km) from Jupiter. As the spacecraft nears its destination, features on the giant planet are increasingly visible, including the Great Red Spot. Juno is approaching over Jupiter’s north pole, providing a unique perspective on the Jupiter system, including its four large moons. The scene was captured by the mission’s imaging camera, called JunoCam, which is designed to acquire high resolution views of features in the Jovian atmosphere from very close to the planet. Image credit: NASA / JPL-Caltech / SwRI / MSSS.

Last week, Juno entered Jupiter’s magnetosphere, where the movement of particles in space is controlled by what’s going on inside the planet.

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

Juno’s science instruments detected changes in the particles and fields around the spacecraft as it passed from an environment dominated by the interplanetary solar wind into the Jovian magnetosphere.

Data from Juno’s Waves investigation 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 gaseous planet’s magnetosphere on June 25.

“The bow shock is analogous to a sonic boom. 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,” said Dr. William Kurth from the University of Iowa, lead co-investigator for the Waves investigation.

Juno has been headed for Jupiter since 2011 to study the gas giant’s atmosphere, aurora, gravity and magnetic field. This infographic illustrates the radiation environments Juno has traveled through on its journey near Earth and in interplanetary space. All of space is filled with particles, and when these particles get moving at high speeds, they’re called radiation. NASA studies space radiation to better protect spacecraft as they travel through space, as well as to understand how this space environment influences planetary evolution. After Jupiter orbit insertion on July 4, Juno will have the chance to study one of the most intense radiation environments in the Solar System. Image credit: NASA’s Goddard Space Flight Center.

“If Jupiter’s magnetosphere glowed in visible light, it would be twice the size of the full Moon as seen from Earth. 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,” he added.

Out in the solar wind, Juno was speeding through an environment that has about 16 particles per cubic inch (one per cubic cm). 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.

The Sun powers spacecraft to Earth orbit, Mars and beyond. Here’s how Juno became the most distant solar-powered explorer and influenced the future of space exploration powered by the Sun. Image credit: NASA / Kim Orr.

“Magnetic fields are produced by what are known as dynamos – convective motion of electrically conducting fluid inside planets,” the scientists said. “As a planet rotates, the electrically susceptible liquid swirls around and drives electric currents, inducing a magnetic field. Earth’s magnetic field is generated by liquid iron in the planet’s core.”

“But with Jupiter, we don’t know what material is producing the planet’s magnetic field. What material is present and how deep down it lies is one of the questions Juno is designed to answer,” said Dr. Jared Espley, Juno program scientist for NASA Headquarters, Washington.

This visual timeline shows our evolving view of Jupiter and some of the key milestones leading up to one of the most ambitious Jupiter missions yet. Image credit: NASA / Kim Orr.

While the transition from the solar wind into the Jovian 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 Dr. Barry Mauk from the Johns Hopkins University Applied Physics Laboratory, instrument lead for Juno’s Jupiter Energetic-Particle Detector Instrument.