Development of a new Phobos spectral simulant: spectral properties from visible to the mid-infrared range

Phobos is the target of the Martian Moons eXploration (MMX), the next sample return mission of the Japanese space agency (JAXA). The mission will investigate the origin of Phobos and Deimos - the two martian moons, using a suite of dedicated instruments. Infrared analysis of the surface composition will be performed by the MIRS spectrometer onboard MMX. Within the scientific studies performed in preparation for the mission, we developed a new laboratory spectral simulant that well reproduces the red and featureless spectrum of Phobos. Our results show that a visible and near-infrared simulant can be developed using dark, opaque materials such as anthracite and coal to reduce the reflectance and absorption features. To investigate the reliability of our proposed simulant in terms of composition and mineralogy, we discussed the similarities and differences in the mid-infrared (MIR) range between our laboratory simulant and some past observations acquired on Phobos. Spectra with different observation geometries were also acquired for our simulant, which give information about grain size and textures of the surface. The simulant developed in our study presents a better match for the Phobos spectrum in the visible and near-infrared compared to the previously proposed simulants.