Mars sample-return mission gained from the "Hayabusa 2" and SLIM missions. Of the two moons, Phobos's orbit is closer to Mars and its surface may have adhered particles blasted from the red planet; thus the Phobos samples collected by MMX may contain material originating from Mars itself. Japan has also shown interest in participating in an international Mars sample-return mission. Since it is currently unknown whether life forms exist on Mars, the mission could potentially transfer viable organisms resulting in back contamination—the introduction of extraterrestrial organisms into Earth's biosphere. The scientific consensus is that the potential for large-scale effects, either through pathogenesis or
Astrobiology restricted to the surfaces of planets. The three most likely candidates for life in the Solar System are the planet Mars, the Jovian moon Europa, and Saturn's moons Titan, and Enceladus. Mars, Enceladus and Europa are considered likely candidates in the search for life primarily because they may have underground liquid water, a molecule essential for life as we know it for its use as a solvent in cells. Water on Mars is found frozen in its polar ice caps, and newly carved gullies recently observed on Mars suggest that liquid water may exist, at least transiently, on the planet's