Europe is to mount a 1 billion-euro mission to Jupiter and its icy moons, moving ahead with an ambitious plan deemed too expensive by the United States.

After more than eight years of review, the European Space Agency (ESA) has given the green light to a space program to explore the giant gas planet and several of its moons - in search of liquid oceans that may harbor life.

The Jupiter Icy Moon Explorer, known as JUICE, is ESA's next "large class" space probe planned under its Cosmic Vision program, which runs from 2015 to 2025.

NASA dropped out

Weighing in at just under five tons, the spacecraft will be one of the heaviest ever to launch to outer planets. It will also be the first solar-powered spacecraft to journey to Jupiter, using massive solar panels to capture enough faint sun rays to keep its instruments running.

NASA had plans to send a spacecraft to Jupiter but later dropped them

JUICE beat out two other missions - the space-based New Gravitational-wave Observatory and an X-ray telescope called ATHENA – in part because it is expected to have fewer cost overruns and technical problems.

The spacecraft was originally intended to fly in tandem with a NASA orbiter that would explore Jupiter's moon Europa, but the US space administration abandoned the plan after an independent planetary study warned the mission would be too costly.

If all goes according to plan, JUICE will lift off aboard an Ariane 5 rocket in 2022, arriving at Jupiter in 2030. It will spend at least three years probing Jupiter and its diverse Galilean moons: the volcanic Io, the icy Europa, and rock-ice Ganymede and Callisto. All the time, it will continuously observe Jupiter's atmosphere and magnetosphere and how the Galilean moons interact with the giant planet.

"Jupiter is the archetype for the giant planets in the solar system and for many giant planets being found around other stars," said Alvaro Gimenez Canete, director of Science and Robotic Exploration at ESA, in a statement. "JUICE will give us better insight into how gas giants and their orbiting worlds form, and their potential for hosting life."

The spacecraft will first visit Callisto and then Europa before it heads to Ganymede, its primary objective.

'Water worlds'

Ganymede, the solar system's biggest moon, is thought to conceal a deep ocean of salty water beneath a thick crust of ice. It's also the only moon in the solar system known to have its own magnetic field, which offers protection against Jupiter's powerful radiation belts.

The Ariane rocket will put JUICE into orbit

Callisto and Europa are also believed to hide an ocean of liquid water beneath layers of ice.

"Studying these 'water worlds' is the next vital step beyond Mars in the search for the conditions for life in our solar system," Andrew Coates, a professor at University College London and a member of the ESA Science Study Team, said in a statement.

"The sub-surface oceans of Europa and Ganymede are now the most exciting 'frontier' in the solar system," Frederic Pont, a physics professor at the University of Exeter in the UK, wrote in an e-mail to DW.

"I don't think we understand enough now about the emergence of life to venture any guess about the habitability of oceans under miles of ice crusts, but it is certainly the most interesting place in the solar system to understand more about the possibility of life elsewhere, now that Mars has turned out to be almost certainly barren."

Four conditions are necessary to establish whether the Galilean moons can possibly host microbial life, according to Emma Bunce, deputy lead scientist for the JUICE proposal and a professor in the Department of Physics and Astronomy at the University of Leicester, which is involved in the program.

They are "water, essential chemical elements, a source of energy and a stable environment over time," she wrote in an e-mail to DW.

In addition to the habitability of the moons, the mission could provide valuable information about how Jupiter interacts with the moons and the role it plays in their potential habitability, Bunce wrote. The knowledge gained "from these water worlds and from Jupiter could provide lessons about extrasolar planets beyond our solar system," she wrote. "There is also the extra serendipitous science that one cannot predict - akin to the discovery of Enceladus plumes by Cassini. If we see something like that on Europa or elsewhere, that would be extra on top of the objectives that we have devised."

Author: John Blau

Editor: Simon Bone