The Japan Aerospace Exploration Agency is preparing to launch an ambitious interplanetary mission designed to journey to the Martian moon Phobos, collect pristine rock and soil samples, and return them to Earth in an approximately five-year voyage. Led by project manager Kawakatsu Yasuhiro for the Martian Moons Exploration Mission, the undertaking aims to shed light on solar system formation, the origins of life, and the potential for utilizing Phobos as a staging ground for future crewed missions to the Martian surface.
Despite their scientific significance, the moons of Mars remain largely uninvestigated. Phobos and its smaller companion, Deimos, are tiny compared to Earth’s Moon, orbiting their parent planet much more closely and at higher speeds. Phobos spans roughly 17 miles at its widest point and completes three orbits around Mars every single day. Nearly half of its surface is dominated by the massive Stickney Crater, the scar of an ancient meteoric impact that nearly fractured the moon entirely. These physical characteristics present formidable engineering hurdles for any landing attempt. Previous historic efforts by Soviet and Russian probes between 1988 and 2011 faced severe challenges, with only the Phobos-2 spacecraft reaching Martian orbit before suffering a catastrophic computer failure just moments before intended touchdown in March 1989.
The upcoming mission represents a collaborative international endeavor spearheaded by Japan with crucial support from international partners. NASA is contributing a specialized scientific instrument known as the Mars-moon Exploration with Gamma Ray and Neutrons detector, or MEGANE. Developed jointly by the Johns Hopkins Applied Physics Laboratory and Lawrence Livermore National Laboratory, the detector is designed to measure gamma ray and neutron energies emitted from the surface of Phobos. This elemental analysis is expected to help resolve a long-standing astronomical debate dating back to the discovery of the moons in 1877: whether Phobos and Deimos were formed from debris blasted off Mars during a massive impact or if they are wandering asteroids captured by planetary gravity.
Planetary scientists note that analyzing volatile elements within the moon’s composition will act much like a genetic test for ancestry. While volatile elements tend to cook off during high-heat impact events, captured asteroids typically retain higher concentrations of them. To gather these crucial specimens, the spacecraft will deploy a tiny German- and French-developed rover named Idefix to scout the terrain and help determine an optimal landing site. Because Phobos possesses exceptionally weak gravity, the mission plans to release its larger lander from a height of less than 350 feet, allowing it to bounce gently onto the surface. The lander, roughly the dimensions of a case of beer, will target two distinct locations on opposite sides of the moon to account for compositional differences between its light and dark hemispheres. Collection mechanisms include an American system utilizing pressurized gas to harvest surface dust alongside a Japanese tool capable of digging approximately one inch into the regolith.
The timeline for the voyage spans roughly five years from launch to recovery. The spacecraft will spend a year traveling to Mars, orbit Phobos for approximately three years while conducting a close flyby of Deimos, and then embark on a one-year return journey. The mission concludes with the targeted splashdown of a heat-shielded sample capsule off the coast of Australia in 2031, with researchers aiming to recover less than half an ounce of material. The schedule also places the Japanese-led endeavor in a race with China’s Tianwen-3 sampling mission, which is similarly slated to return samples from the Martian system around 2031.
