Juno will orbit Jupiter more than 30 times over the course of a year at the end of its 400-million-mile journey, its nine onboard instruments studying the composition of the planet, its atmosphere, gravity and powerful magnetic field — the most powerful of all the planets.

"When the cloud of material that eventually became our solar system formed, most of it went into the sun, and then all the leftovers made our solar system," said Scott Bolton, director of space science at Southwest Research Institute and the lead scientist for Juno.

"Most of those leftovers went into Jupiter," Bolton added. "So we go back to Jupiter to try to figure out, OK, what exactly was in those leftovers, and what state were they in that allowed all of the planets to be formed and for Earth to be made and life to begin? We're looking to discover the recipe for planets, if you will, and we're back at the ingredient list."

A 'real close' look

Like the sun, Jupiter is mostly hydrogen and helium. What scientists don't know, however, is whether the planet began with a dense, planetary core that drew in those gases through gravity, or with some collapse in the original cloud, or nebula, that also created the sun.

"Juno goes in real close to Jupiter, and doing so, it is able to map out at very high resolution both (gravitation and magnetic) fields," said Randy Gladstone, an institute scientist who will study the planet's aurora with one of two locally designed instruments on the mission. "The gravity field gives you the inside structure of Jupiter, whether it has a core, that will help answer questions about the solar system."

Because Jupiter is largely made of gases, scientists will be able to study the highly pressurized hydrogen that forms the engine, or dynamo, of the planet's powerful magnetic field.

"The Earth has this little liquid core of iron, just outside its solid core of iron, where the dynamo arises," Gladstone said. "But it's hard to see the Earth's magnetic field that deep because it's shielded by all the junk above it. Whereas Jupiter doesn't have that stuff in the way. They'll learn a lot more about dynamos from Juno because they'll be able to see these little effects way down deep."

Powered by solar panels

Among the unusual aspects of Juno is its power source. Rather than the traditional plutonium reactor powering its instruments, Juno will use three large solar panels spanning 66 feet, making it NASA's first solar-powered craft designed to operate so far from the sun.

It also will fly in an orbit over Jupiter's poles, rather than around its equator, where Galileo, the first NASA mission to Jupiter, which ended in 2003, flew. That polar orbit will minimize exposure to the planet's powerful radiation fields. Even so, the sensitive instruments will be protected by a heavy, titanium "vault," or shield.

"It's very much like an armored tank going to Jupiter," Bolton said.

The probe itself will be launched atop an Atlas V-551 rocket expected to reach Jupiter in July 2016. After completing its mission, the spacecraft will be sent crashing into the planet.

Juno is the second spacecraft under NASA's New Frontiers program. New Horizons, a mission to Pluto's moon Charon launched in 2006, also led by Southwest Research scientists, was the first. It also gathered information from Jupiter when it flew by in 2007.

dfinley@express-news.net