CAPE CANAVERAL, Fla. - The Juno spacecraft was prepared on Thursday for its August 5 launch for a five-year journey to Jupiter.The robotic probe called Juno is scheduled to spend one year cycling inside Jupiter's deadly radiation belts, far closer than any previous orbiting spacecraft, to learn how much water the giant planet holds, what triggers its vast magnetic fields and whether a solid core lies beneath its dense, hot atmosphere."Jupiter holds a lot of key secrets about how we formed," said lead scientist Scott Bolton, with the Southwest Research Institute in San Antonio, Texas.Scientists believe Jupiter was the first planet to form after the birth of the sun, though exactly how that happened is unknown. One key piece of missing data is how much water is inside the giant planet, which circles the sun five times farther away than Earth.Jupiter, like the sun, is comprised primarily of hydrogen and helium, with a sprinkling of other elements, like oxygen. Scientists believe the oxygen is bound with hydrogen to form water, which can be measured by microwave sounders, one of eight science instruments on Juno.Jupiter's water content is directly tied to where -- and how -- the planet formed. Some evidence points to a planet that grew in the colder nether-regions of the solar system and then migrated inward. Other computer models show Jupiter formed at about its present location by accumulating ancient icy snowballs.However it grew, Jupiter ended up with a mass more than twice all its sister planets combined, giving it the gravitational muscle to hang on to nearly all of its original building materials."That's why it's very interesting to us if we want to go back in time and understand where we came from and how the planets were made" -- which Juno can help NASA do, Bolton said.