After nearly a five year wait, scientists at NASA will get their very first close-encounter with Jupiter.

Launched in August of 2011, the Juno spacecraft will enter into orbit around the largest planet in the solar system on July 4 after a 716-million km journey.

Yesterday, NASA's Jet Propulsion Laboratory opened the doors to one of their 'clean rooms' which held a large, 1/4 scale model of Juno, as well as a full-size, test replica of one of its solar panel wings.

Juno is to spend a year in an unprecedented polar orbit around the giant planet, measuring its water content, mapping its magnetic fields and searching for signs of a solid core.

With more than twice the mass than all its sibling planets combined, Jupiter is believed to hold a key piece to the puzzle of how the planets formed some 4.65 billion years ago from the gas and dust left over after the birth of the sun.

To make its observations, Juno will soar as close as 5,000 km above Jupiter's cloud tops, the first spacecraft to fly inside the planet's radiation belts.

Juno should last through 33 orbits around Jupiter, which is about a year on Earth. Its last manoeuvre will be a suicidal plunge into the planet's thick atmosphere, which will incinerate the probe to avoid possible contamination of Jupiter's water-bearing moons.