Juno sets off on 5-year trip to Jupiter

By Marcia Dunn
Associated Press / August 6, 2011

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CAPE CANAVERAL, Fla. - A sun-powered robotic explorer named Juno is rocketing toward Jupiter on a fresh quest to learn more about how the solar system was formed.

Hundreds of scientists and their families and friends - among thousands of invited guests - cheered and yelled “Go Juno!’’ as the unmanned Atlas rocket blasted into a clear midday sky yesterday. It will take five years to reach Jupiter, the solar system’s most massive and ancient planet.

“Next stop is Jupiter,’’ exulted Scott Bolton, Juno’s principal investigator and an astrophysicist at Southwest Research Institute in San Antonio.

Within an hour of liftoff, the spacecraft hurtled out of Earth’s orbit at 24,000 miles per hour on a roundabout course for Jupiter. It was expected to whip past the orbit of the moon in half a day, early this morning.

It is the first step in Juno’s 1.7 billion-mile, $1.1 billion voyage to the gaseous Jupiter, just two planets away but altogether different from Earth and next-door neighbor Mars.

Juno is solar powered, a first for a spacecraft meant to roam so far from the sun. The three huge solar panels popped open an hour into the flight, each one stretching as long and wide as a tractor-trailer. Previous spacecraft to the outer planets have relied on nuclear energy.

With Juno, scientists hope to answer some of the most fundamental questions on our solar system. “How Jupiter formed. How it evolved. What really happened early in the solar system,’’ Bolton said.

Bolton said Jupiter is like a time capsule. It got most of the leftovers from the sun’s creation nearly 5 billion years ago - hence the planet’s immense size - and its enormous gravity field has enabled it to hold on to that original material. Astronomers say it probably was the first planet in the solar system to form.

Juno will venture much closer to Jupiter than any of the eight spacecraft that have visited since the 1970s, most of them just passing by.

If all goes well, Juno will go into orbit around Jupiter’s poles - a first - on July 4, 2016.

The oblong orbit will bring Juno within 3,100 miles of the cloud tops and right over the most powerful auroras in the solar system.

Juno will circle the planet 33 times, each orbit lasting 11 days, for a grand total of one year.

It will measure Jupiter’s invisible gravity and magnetic force fields. It also will try to ascertain the abundance of water and oxygen in the atmosphere, and determine whether the core of the planet is solid or gaseous.