Galileo's successor: The only probe to have orbited Jupiter so far was Galileo which arrived in 1995 and met its fiery demise plunging into the atmosphere in 2003.

Credit: NASA, ESA, A. Simon-Miller (Goddard Space Flight Center), I. de Pater, M. Wong (UC Berkeley)

SYDNEY: The U.S. space agency, NASA, is moving forward on a mission to conduct an unprecedented, in-depth study of the gas giant Jupiter.

Called Juno, the mission will be the first in which a spacecraft is placed in a highly elliptical polar orbit to understand the giant planet's formation, evolution and structure.

Underneath its dense cloud cover, Jupiter safeguards secrets to the fundamental processes and conditions that governed our early Solar System.

Fundamental secrets

"In Greek and Roman mythology, Jupiter's wife Juno peered through Jupiter's veil of clouds to watch over her husband's mischief," said Toby Owen, co-investigator behind the mission at the University of Hawaii in Honolulu.

"Our Juno looks through Jupiter's clouds to see what the planet is up to, not seeking signs of misbehaviour, but searching for whispers of water, the ultimate essence of life," he said.

The robotic probe is scheduled to launch aboard an Atlas rocket from Cape Canaveral, Florida, in August 2011, reaching Jupiter in 2016.

The craft will orbit Jupiter 32 times, skimming about 4,800 km over the planet's cloud tops for approximately one year. The mission will be the first solar powered spacecraft designed to operate despite the great distance from the Sun.

"Jupiter is more than 644 million kilometres (400 million miles) from the Sun or five times further than Earth," said Scott Bolton, Juno principal investigator with the Southwest Research Institute in San Antonio, Texas. "Juno is engineered to be extremely energy efficient."

Colourful clouds

The spacecraft will use a camera and nine science instruments to study the hidden world beneath the planet's colourful clouds. The suite of science instruments will investigate the existence of an ice-rock core, Jupiter's intense magnetic field, water and ammonia clouds in the deep atmosphere, and explore the planet's aurora borealis.

"Jupiter is the archetype of giant planets in our solar system and formed very early, capturing most of the material left after the Sun formed," said Bolton. "Unlike Earth, Jupiter's giant mass allowed it to hold onto its original composition, providing us with a way of tracing our Solar System's history."

Understanding the formation of Jupiter is essential to understanding the processes that led to the development of the rest of our Solar System and what the conditions were that led to Earth and life, the experts said.

Similar to the Sun, Jupiter is composed mostly of hydrogen and helium. A small percentage of the planet is composed of heavier elements. However, Jupiter has a larger percentage of these heavier elements than the Sun.

"Juno's extraordinarily accurate determination of the gravity and magnetic fields of Jupiter will enable us to understand what is going on deep down in the planet," said Dave Stevenson, co-investigator for the mission at the California Institute of Technology in Pasadena.

"These and other measurements will inform us about how Jupiter's constituents are distributed, how Jupiter formed and how it evolved, which is a central part of our growing understanding of the nature of our Solar System," he said.

Metallic hydrogen

Deep in Jupiter's atmosphere, under great pressure, hydrogen gas is squeezed into a fluid known as metallic hydrogen. At these great depths, the hydrogen acts like an electrically conducting metal which is believed to be the source of the planet's intense magnetic field. Jupiter also may have a rocky solid core at the centre.

"Juno gives us a fantastic opportunity to get a picture of the structure of Jupiter in a way never before possible," said James Green, director of NASA's Planetary Division at NASA Headquarters in Washington DC. "It will allow us to take a giant step forward in our understanding on how giant planets form and the role that plays in putting the rest of the Solar System together. "

The Juno mission is the second spacecraft designed under NASA's New Frontiers Program. The first was the Pluto New Horizons mission, launched in January 2006 and scheduled to reach Pluto's moon Charon in 2015.