Sen—In August 2011 NASA's Juno spacecraft launched on its long 5 year journey to Jupiter. Having performed two deep space manoeuvres earlier this year, the space craft is currently heading back towards the inner Solar Sytstem for a gravity assist flyby of Earth in October 2013 that will set it on course to arrive at Jupiter in July 2016.

On arrival Juno will be placed in a polar orbit. It's main mission is to understand the origin and evolution of Jupiter; to determine how much water is in Jupiter's atmosphere and measure its composition, temperature, cloud motions and deep winds, which will help scientists understand the planet's formation. It will map Jupiter's magnetic and gravity fields, to reveal the planet's deep structure. Juno will also study Jupiter's magnetosphere near the poles to find out how the planet's enormous magnetic force field affects its atmosphere. After 33 orbits of Jupiter, Juno will de-orbit and crash into the planet in October 2017.

Artist illustration of the Juice probe. Credit: ESA

Four years later, in 2022 the European Space Agency (ESA) plans to launch its own spacecraft to Jupiter. Called "Juice" - Jupiter Icy Moon Explorer - it will take seven and a half years to reach Jupiter where it will spend three and half years performing detailed investigations of Jupiter and its three ocean-bearing moons Europa, Callisto and Ganymede, with particular emphasis on Ganymede as a planetary body and potential habitat.

Arriving in 2030 The mission around the Jovian system will involve orbit insertions at Jupiter and Ganymede and the large number of flyby manoeuvres, over 25 gravity assists and two Europa flybys.

The main science objectives at Ganymede and Callisto will include study of the ocean layers and any subsurface water reservoirs; topographic, geologic and composition mapping of the surface; study of the icy crusts and mass distribution, dynamics and evolution of the interiors; investigations of the exospheres and in the case of Ganymede study its magnetic field and how that interacts with Jupiter's magnetosphere.

For Europa the focus is on the chemistry essential to life, including organic molecules and study of surface features and the composition of the non water-ice material. Juice will provide the first subsurface sounding of the moon and the first determination of the minimal thickness of the icy crust over the most recently active regions.

The circulation, meteorology, chemistry and structure of Jupiter will be studied from the cloud tops to the thermosphere, over a sufficiently long time period and wide latitudinal coverage to investigate evolving weather systems and the mechanisms of transporting energy, momentum and material between the different layers.

"Jupiter is the archetype for the giant planets of the Solar System and for many giant planets being found around other stars," says Prof. Alvaro Gimenez Canete, ESA's Director of Science and Robotic Exploration. "Juice will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life."