"Three, two one, ignition and liftoff of the Atlas 5 with Juno on a trek to Jupiter, a planetary piece of the puzzle on the beginning of our solar system," called launch commentator George Diller.
The Atlas rocket left from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida, rising quickly into muggy skies. It was delayed nearly an hour by a suspected helium leak, and by a small boat in the nearby Atlantic that wandered too close to the launch pad before the Coast Guard could chase it away. It was NASA's first launch since the final space shuttle last month.
The $1.1 billion Juno project is meant to survey giant Jupiter -- it is 318 times at massive as Earth, with a diameter of some 85,000 miles -- to determine how it formed, how it became so large, and see whether there is oxygen in its thick, cold atmosphere.
Size matters when it comes to planets. Scientists have suggested that because of Jupiter's powerful gravity (something that weighs 100 pounds on Earth would weigh 236 pounds there), the planet swallowed up many wandering asteroids and other debris left over as the solar system formed -- natural space junk, some of which might otherwise have crashed into the young Earth and perhaps prevented the formation of life here.
"If we're going to learn who we are and where we came from, and how the Earth works, we've got to keep doing these science missions, not just Juno," said Scott Bolton of the Southwest Research Institute and Juno's principal investigator.
The ship is expected to reach Jupiter in July 2016 and orbit the planet, passing over its poles, for at least a year. When its mission is over, the plan is to send the ship plunging into the planet's clouds. NASA doesn't want it wandering around among Jupiter's 50-some moons and possibly crashing into one of them
Landing on Jupiter is out of the question. Scientists say there's probably no actual surface there to land on. While smaller worlds (think of the moon or Mercury) can't prevent their atmospheres from escaping into space, Jupiter appears to be all atmosphere -- with swirling clouds of ammonia and methane, which form distinctive bands visible in pictures and become thicker and thicker the deeper one goes.
If one could dive into the Jovian atmosphere without being crushed, one would find pressure and temperature increasing to such levels that the atmosphere becomes liquid and eventually metallic, creating powerful magnetism. Deep down in the center, some scientists think there may be a rocky core no larger than Earth. But nobody knows, which is why Juno was conceived.
In Roman mythology, Jupiter, the king of the gods, cloaked himself in clouds to hide his mischief, but his wife, Juno, was able to see through them. NASA says Juno, the spacecraft, will do much the same thing.
The ship has three giant solar panels so that it will be able to be powered by the sun's feeble light from nearly half a billion miles away. The panels give it a diameter of about 66 feet in flight. It will turn three times a minute for stability, pointing its color camera, particle detectors and other instruments at Jupiter's cloud tops.
On the lighter side, it also carries three small figurines representing Jupiter, Juno and the scientist Galileo, who first looked at Jupiter through a telescope. There's a bit of marketing going on there -- the little figures are made by Lego.
(Above: NASA artist's conception of Juno orbiting Jupiter.)