Hundreds of scientists and their families and friends watched from just a few miles away, cheering and yelling, “Go Juno!”, as the spacecraft soared into a clear midday sky atop an unmanned rocket.
“It’s fantastic!” said Dr Fran Bagenal, a planetary scientist at the University of Colorado at Boulder, who is part of the project. “Just great to see the thing lift off.”
It was the first step in Juno’s 1.7bn-mile (2.7bn km) voyage to the gas giant Jupiter, just two planets away but altogether different from Earth and next-door neighbour Mars.
Juno is solar powered, a first for a spacecraft meant to roam so far from the sun. It has three huge solar panels that were folded for launch. Once opened, they should each stretch 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 that eventually led to all of us,” said Juno’s chief investigator Scott Bolton, an astrophysicist at Southwest Research Institute in San Antonio.
Bolton said Jupiter is like a time capsule. It got most of the leftovers from the sun’s creation nearly 5bn years ago, hence the planet’s immense size. Its enormous gravity field has enabled it to hold on to that original material.
Jupiter is so big it could hold everything in the solar system, apart from the sun, and still be twice as massive. 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 the planet since the 1970s. Juno represents the next step, Bolton said.
“We look deeper. We go much closer. We’re going over the poles. So we’re doing a lot of new things that have never been done, and we’re going to get all this brand-new information,” Bolton said.
If all goes well, Juno will go into orbit around Jupiter’s poles – a first – on 4 July 2016.
The oblong orbit will bring Juno within 3,100 miles of the cloudtops and right over the most powerful auroras in the solar system. In fact, that’s how the spacecraft got its name – Juno peered through clouds to keep tabs on her husband, Jupiter.
Juno will circle the planet 33 times, each orbit lasting 11 days for a grand total of one year.
With each orbit, the spacecraft will pass over a different longitude so that by mission’s end, “we’ve essentially dropped a net around the planet with all of our measurements,” Bolton said. That’s crucial for understanding Jupiter’s invisible gravity and magnetic force fields, he noted.
The $1.1bn mission will end with Juno taking a fatal plunge into Jupiter in 2017.
Unlike many other Nasa missions, this one came in on budget and on time. It’s relatively inexpensive: the Cassini probe, launched in 1997 to Saturn by way of Jupiter, cost $3.4bn.