Blastoff was delayed almost an hour while engineers worked around a problem with a helium purge line in the rocket’s ground support equipment, but the glitch was resolved and the 191-foot tall booster lifted off at 12:25 p.m. EDT. It’s the first step in a 445-million mile, five-year journey to Jupiter, the largest planet in the solar system.
Juno is designed to ferret out secrets about how the solar system formed out of the gas and dust that wasn’t swept into the sun. More than half of the leftovers went into Jupiter, a planet so large that scientists believe its hefty gravity has allowed it to keep hold of even the lightest of its original building blocks, hydrogen and helium.
The next item on the planetary ingredient list is oxygen and finding out how prevalent it is in Jupiter is among the primary goals of Juno. Upon arrival on July 4, 2016, Juno will slingshot itself into an unprecedented polar orbit that will bring it to within 3,100 miles of the planet’s massive cloud tops. Among its eight science instruments are chemical sensors, microwave sounders and magnetometers to look for water, measure gravity and map Jupiter’s massive magnetic fields, the most powerful in the solar system after the sun’s.
“We’re really looking for the recipe for planet formation,” Juno lead scientist Scott Bolton, with the Southwest Research Institute in San Antonio, Texas, said shortly before the launch. We’re going after the ingredients of Jupiter by getting the water abundance as well as very precise measurements of the gravity field that will help us understand whether there’s a core of heavy elements or a core of rocks in the middle of Jupiter,” he said.
The measurements will help scientists discriminate among theories about what the early solar system looked like and how Jupiter, believed to be the first planet to form, was created. Juno will last about year in the harsh radioactive environment at Jupiter. Its last move will be to dive into the planet’s thick atmosphere, where it will be incinerated, avoiding a potential contamination of Jupiter’s water-bearing moons.