The Martian Moons eXploration (MMX) mission is in development by the Japan Aerospace Exploration Agency (JAXA). Scheduled for launch in 2024, the MMX spacecraft plans to visit both of the martian moons, Phobos and Deimos, land on the surface of the larger moon Phobos, collect a surface sample, and then deliver that sample to Earth. On behalf of NASA, Johns Hopkins Applied Physics Laboratory (APL) is leading and building one of the spacecraft's science instruments: a gamma-ray and neutron spectrometer named MEGANE (an acronym for Mars-moon Exploration with GAmma rays and NEutrons, pronounced 'meh-gah-nay), which will measure the elemental composition of Phobos.
MEGANE means "eyeglasses" in Japanese, and the instrument will give MMX the ability to "see" the elemental composition of Phobos by measuring the naturally emitted gamma rays and neutrons. These gamma rays and neutrons are generated by cosmic rays that continually bombard Phobos' surface, and from natural radioactivity in its surface rocks. MEGANE's compositional measurements will provide key information to help determine whether Phobos is a captured asteroid or the result of a larger body hitting Mars. MEGANE data will also be used to study surface processes on Phobos and to support site selection for the MMX-gathered samples that will be delivered to Earth, providing critical context for those samples.