Why Go Back to Jupiter? For the Surprises

A tough little robot named Juno is circling, looking into the origins of the biggest planet and the history of our own.

Out there.

Photographer: ROBYN BECK/AFP/Getty Images

Why go back to Jupiter? NASA has already sent enough spacecraft to know that there’s nobody up there, and that it’s all bad real estate. The atmosphere is a choking mixture of hydrogen and helium laced with ammonia clouds. It’s roiled with storms, blasted with X-rays and bitterly cold. There’s no discernible solid surface.

On the plus side, there’s a lot to explore for the latest craft, a tough little robot called Juno, which successfully began orbiting the fifth planet from the sun late on Monday. Jupiter is 300 times the mass of Earth -- more than twice the mass of all the other planets combined -- and it has at least 67 moons.

Juno is designed to see what’s beneath the cloud tops, giving clues to how the planet formed and thereby shedding light on how our planet was born.

The craft will orbit over the poles, a change from the previous craft, Galileo, which orbited near the equator. Juno is designed to withstand radiation that would have fried its predecessors, so it can plunge much closer to the cloud tops and take data and images never before possible.

Jupiter was the first of the solar system’s planets, said Jonathan Lunine, a Cornell professor and mission co-investigator. Nobody knows exactly how it formed, or where, given that the adolescent planets may have jostled each other around during the dawn of the solar system’s 4.6-billion-year history.

Jupiter is so massive that its formation influenced everything that followed, including the birth of our planet. In its formative stage, the solar system was a swirl of rocky and icy debris. Jupiter both deflected debris that would have come near the embryonic Earth, and flung debris from Earth’s neighborhood outward.

So knowing Jupiter’s story is a key to our own, and despite the previous trips, scientists have barely scratched the surface. The Pioneer and Voyager missions flew by Jupiter and in the 1970s and showed that its major moons were worlds in their own right. The Galileo mission, which arrived in 1995, was the first ever to go into orbit. But there was a glitch. An umbrella-shaped antenna failed to unfurl, so data could only be sent back to mission control in a slow trickle via a backup antenna.

Despite this disappointment, Galileo sent back crisp pictures of the Jovian moons Ganymede, Callisto, Io and Europa that looked like they’d been taken from an airplane window. The images of Europa’s icy surface revealed features that confirmed that there was an ocean underneath -- one that might be warmed enough by the friction of Jupiter’s tidal pull to harbor life.

Launched in 2011, Juno was part of a series of three missions called New Frontiers, which are supposed to deliver more bang for fewer bucks by undergoing outside budget reviews. The other two include the New Horizons mission, which delivered spectacular images of Pluto last summer, and an upcoming mission to visit an asteroid and return a sample.

Juno uses enormous solar panels to catch the meager sunlight of the outer solar system. A titanium vault will protect the instruments from Jupiter’s radiation belts. At its closer approach each orbit, Juno will be 2,500 miles above the clouds, an order of magnitude closer than Galileo.

Instruments will measure Jupiter’s magnetic fields, dramatic polar auroras and the gases making up it’s vast atmosphere. Juno will also take precise measurements of Jupiter’s gravitational field, which should reveal something about the interior. Scientists infer that deep inside, the intense pressure forces hydrogen into an exotic liquid state. Deeper inside may be a rocky core about the size of Earth.

If history is any guide, there will be surprises. Earlier missions have shown that the innermost planet Mercury has a magnetic field, that Venus is whipped by powerful winds, that Jupiter’s moon Io is bursting with volcanoes and Europa holds an ocean, said David Stevenson, a co-investigator on Juno and professor at Caltech. Pluto, Saturn and Saturn’s moons were dramatically different from their appearance through telescopes.

“I’d argue that’s the central message,” he said. “When we go somewhere, we’re surprised.”

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

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