Measuring the Elemental Composition of Phobos: The Mars‐moon Exploration with GAmma rays and NEutrons (MEGANE) Investigation for the Martian Moons eXploration (MMX) Mission

Abstract

The Mars-moon Exploration with GAmma rays and NEutrons (MEGANE) investigation will use gamma-ray and neutron spectroscopy to measure the elemental composition of Mars' moon Phobos. MEGANE is part of the Japanese Martian Moons eXploration (MMX) mission that will make comprehensive remote sensing measurements of both of Mars' moons Phobos and Deimos. MMX will also return to Earth regolith samples of Phobos. The science goals of the MEGANE investigation mirror those of the MMX mission. MEGANE will use elemental composition measurements to determine if Phobos is a captured asteroid or the end result of a giant impact event on Mars, study Phobos surface processes, provide reconnaissance to support the sample site selection, and supply compositional context for the returned samples. To accomplish its measurements, MEGANE will use a high-purity Ge gamma-ray spectrometer (GRS), and a neutron spectrometer (NS) that consists of two 3 He gas proportional neutron sensors. The GRS derives heritage from similar instruments from NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging mission and the Psyche mission that is currently in development; the NS is based on similar instruments used for NASA's Lunar Prospector and Psyche missions.

Characterization of D‐Type Spectra Based on Hyperspectral Remote Sensing of the Lunar Surface

“…In any case, it is difficult to obtain a definitive answer regarding composition only from remote‐sensing data, especially for featureless spectra without diagnostic absorption bands. Future in situ analysis and sample return missions targeting Phobos and Deimos (e.g., MMX; Martian Moons eXploration, which is being developed by JAXA [Lawrence et al., 2019]) would provide important constraints for this issue.…”

The Importance of Phobos Sample Return for Understanding the Mars-Moon System

“…Such a volatile-rich nature relative to the Earth and Moon is evident in ratios of K/Th and K/U (volatile/refractory incompatible element) ( Fig. 5) and the K/Th ratio of Phobos surface will be measured by MEGANE (Lawrence et al 2019). On the other hand, in-situ formation by co-accretion with Mars would provide a bulk chemistry represented by the chondritic bulk Mars.…”

“…To prevent sample contamination from thruster plume products and regolith particles that could be ejected from the surface during a thrust descent, the spacecraft will employ ballistic descent to reach a point directly above a landing site before a final free-fall descent without a thruster jet (Kawakatsu et al 2017;Kawakatsu et al 2019). Seven nominal science instruments comprise several payloads for the remote sensing observations (Kuramoto et al 2018): 1) a narrow-angle camera (TElescopic Nadir imager for GeOmOrphology, TENGOO) (JAXA) (Kameda et al 2019), 2) a wide-angle multispectral camera (Optical RadiOmeter composed of CHromatic Imagers, OROCHI) (JAXA) (Kameda et al 2019), 3) a near-infrared spectrometer (0.9-3.6 µm) MMX Infrared Spectrometer, MIRS (CNES), 4) a light detection and ranging instrument (LIDAR) (JAXA), 5) a dust instrument for particle sizes >10 µm (Circum-Martian Dust Monitor, CMDM) (JAXA) (Kobayashi et al 2018), 6) a gamma-ray and neutron instrument (Mars-moon Exploration with GAmma rays and Neutrons, MEGANE) (NASA) (Lawrence et al 2019), and 7) an ion mass spectrometer (Mass Spectrum Analyzer, MSA) (JAXA). Along with these seven instruments, the MMX spacecraft will carry and deploy a Rover (CNES/DLR) for in-situ surface exploration (Ulamec et al 2019).…”

Martian Moons Exploration MMX: Sample Return Mission to Phobos Elucidating Formation Processes of Habitable Planets

“…Hydrous minerals are a very important proxy indicative of the captured origin of the moon, thus OROCHI and MIRS are designed to detect absorption bands at ~0.7 µm and ~2.7 µm, respectively, caused by hydroxyl group in mineral structures with sufficient signal to noise ratio. MEGANE (Lawrence et al 2019), the gamma-ray and neutron spectrometer will determine the concentration of elements such as Si, Fe, H, and K in the surface layer of several tens cm thickness, where cosmic-ray induced and spontaneous atomic nucleus reactions take place associated with emissions of neutrons and high energy photons to space, over the hemisphere scale. MSA (Yokota et al this issue.…”