Overview and Science of MMX

MMX (Martian Moons eXploration) is the 3rd sample return mission of JAXA/ISAS following Hayabusa and Hayabusa2. The MMX spacecraft will be launched in 2024 by an H-III rocket and make a round trip to the Martian system ~5 years. In the proximity of the Martian moons for 3 years, MMX will observe them along with the Martian atmosphere and surrounding space and conduct multiple landings on Phobos to collect Phoboss-indigenous materials. Owing to the lack of definitive evidence, the origin of Phobos and Deimos is under debate between the two leading hypotheses: the capture of volatile-rich primordial asteroid(s) and the in-situ formation from a debris disk that generated by a giant impact onto early Mars. Whichever theory is correct, the Martian moons likely preserve key records on the evolution of the early solar system and the formation of Mars. Through close-up observations of both moons and sample return from Phobos, MMX will settle the controversy of their origin, reveal their evolution, and elucidate the early solar system evolution around the region near the snow line. Global circulation and escape of the Martian atmosphere will also be monitored to reveal basic processes that have shaped and altered the Martian surface environment. The MMX spacecraft consists of three modules with chemical propulsion systems. By releasing used modules at appropriate timings, the spacecraft mass is reduced to allow orbital tuning to quasi-satellite orbits around Phobos, landings on Phobos surface, and the escape from the Martian gravity to return to the Earth. MMX will arrive at the Martian system in 2025 and start close-up observations of Phobos from quasi-satellite orbits. Among the total of 7 mounted instruments for scientific observations, TENGOO (telescope camera) and LIDAR will conduct high-resolution topography mapping and OROCHI (multi-band visible camera), MIRS (infra-red spectrometer provided by CNES), MEGANE (gamma-ray and neutron spectrometer provided by NASA), and MSA (ion mass spectrum analyzer) will survey surface composition and its heterogeneity. Hydrous minerals and interior ice are important observational targets because they, if identified, strongly support the capture hypothesis. Data taken by these instruments will be also useful for the landing site selection and characterization. Before the first landing, a rover (provided by CNES/DLR) will be released near the sampling site to collect data on surface regolith properties to be referred for the mothership landing operation. The rover will carry cameras, miniRAD (thermal mapper), and RAX (laser Raman spectrometer) to collect data on the physical and mineralogical characteristics of the Phobos surface around the sampling site. In early 2027, Mars will come to its closest approach to the Earth which minimizes the communication delay between the spacecraft and the Earth station. Together with the timing relatively far from Sun-Mars conjunctions and the Martian equinoxes, this period is the most favorable for landing operations that need real-time communication with the ground station and solar illumination undisturbed by eclipses. MMX will use two sampling systems, the C-sampler using a coring mechanism equipped on the tip of a manipulator and the P-sampler (provided by NASA) using a pneumatic mechanism equipped on a landing leg. After the stay near Phobos, the MMX spacecraft will be transferred to Deimos-flyby orbits to conduct Deimos observations, and then the return module will depart the Martian system in 2028. During the stay in the Martian system, MMX will also conduct wide-area observations of the Martian atmosphere using imagers (OROCHI, MIRS, and TENGOO) to study the atmospheric dynamics and the water vapor and dust transport. Simultanenousely, MSA will survey ions not only released and sputtered from Phobos's surface but also escaped from the Martian upper atmosphere. CMDM (dust monitor) will continuously survey the dust flux around the moons to assess the processes of space weathering by micrometeoroid bombardments and the possible formation of dust rings along the moons’ orbits. The sample capsule will come back to the Earth in 2029. Complimentarily with remote sensing studies, returned samples will provide us strong cosmo-chemical constraints for the origin of Phobos as well as those for early solar system processes.