— Europe is considering a mission to Jupiter's icy moons to assess their suitability for life.
— The probe would study Europa and Callisto before settling into an orbit around Ganymede.
— The moons may be similar to some of the planets that have been found circling stars beyond the solar system.
Hoping to better understand conditions where life can form and grow, scientists want to explore three of Jupiter's large icy moons which may resemble some of the planets found orbiting stars beyond our solar system.
Europa, Callisto and Jupiter's largest moon, Ganymede, are all believed to have liquid oceans beneath their icy shells, as well as organic chemistry and possible sources of energy beyond the dim amount of sunlight that reaches their distant surfaces. These are all conditions that may be required for life in much more distant planetary bodies.
"We thought for quite some time these were dead icy bodies, but we have recently actually discovered a fabulous collection of very geologically active things there," planetary scientist Athena Coustenis, with the Paris Observatory in France, said at the Astrobiology Science Conference in Atlanta this week.
A newly proposed mission, The Jupiter Icy Moons Explorer, nicknamed JUICE, would send a spacecraft to study the three moons and their habitability.
Mission planners selected Ganymede as an archetype of an exoplanet water world like GJ 1214b, a super-Earth discovered last year circling a star about 40 light-years from Earth.
"We think it is the best example of a liquid environment trapped between icy layers," JUICE science study team member Olga Prieto Ballesteros, with the Center of Astrobiology in Madrid, Spain, said during a presentation at the conference.
Europa poses an intriguing model to those exploring the possibility of alien life because its buried ocean is believed to be in direct contact with the moon's silicate mantle, a source of salts and other elements. Europa is thought to be like exoplanets that are between water worlds and Earth-like bodies.
Callisto was selected because it is the only known example of a non-active, but ocean-bearing world, Prieto Ballesteros said.
"The icy planetary bodies have opened the possibility to find habitats in deeper environments. We can say that these icy bodies will expand the classical concept of habitability," which previously was limited to places with liquid water on the surface, Prieto Ballesteros said.
"The key question is are these worlds habitable?" she said.
JUICE's job will be to characterize the moons using cameras, multiple-wavelength spectrometers for chemical analysis, magnetic field detectors, particle sensors, sounders and radio science instruments.
"These instruments are very useful to study the habitability of these satellites' environments," Prieto Ballesteros wrote in an email to Discovery News.
With them, JUICE will be able to assess the moons' underground liquid reservoirs and analyze their surface chemistry, including any organic compounds.
"We think it's a necessary step in the astrobiological exploration of the solar system," she said.
Apparently, the European Space Agency's Science Program Committee agrees. The panel this week selected JUICE from among three projects vying for funding. It will now be considered by representatives from the European Space Agency's 19 member states on May 2.
JUICE's competitors are an X-ray telescope for high-energy physics called ATHENA and the NGO observatory designed to search for gravitational waves.
If selected, JUICE would launch in June 2022 and reach Jupiter in 2030. The mission is designed to last 3.5 years.