Toward Landed Multiview-Multispectral Sensing from the Martian Moons eXploration Spacecraft: Imaging Ryugu & Bennu Samples with the Laboratory OROCHI Simulator

The JAXA Martian Moons eXploration (MMX) mission will address the question of the origin of Phobos and Deimos by launching a spacecraft to the Mars system in 2026, performing dedicated surveys of the moons, and by collecting a sample from the surface of Phobos and returning it to Earth in 2031 [1]. OROCHI is a wide-angle visible-to-near-infrared (VNIR) 8-channel 8-camera multispectral imaging system for MMX, with a key objective of characterising the surface spectral diversity of the moons from orbit, during descent, and once landed on the surface of Phobos [2]. In the landed configuration OROCHI will reside 80 cm above the Phobos surface, such that the lateral displacements (of 10 cm) between the channel optical axes result in each spectral channel observing the surface with a distinct phase angle.

Here we investigate the implications of this novel multiview-multispectral observation scenario on the recovery of Phobos-like surface spectral reflectance features by imaging pristine grains of asteroids Ryugu and Bennu, collected in aggregate and hosted at the JAXA Extraterrestrial Sample Curation Centre (Ryugu sample “C9003” and Bennu sample “ORX-19000”), with a laboratory simulator of OROCHI [3]. Complementing visible (450 – 750 nm) hyperspectral imaging studies of the phase-dependence of Bennu and Ryugu spectral slope features [4, 5], here we report on observations of the phase-dependence over the OROCHI band profiles (390, 480, 550, 650, 730, 860 & 950 nm).

Remote sensing observations of Ryugu and Bennu show that these bodies each exhibit phase-dependent spectral features (phase reddening), with macroscopic surface roughness and microscopic multiple scattering both as candidate causes, with varying contributions across spatial scales [7, 8]. Phobos also exhibits phase-reddening, to various degrees across the surface, with sub-micron roughness hypothesized as the dominant cause [9]. By measuring the phase-dependence of Ryugu and Bennu spectral features at the sub-mm to mm spatial resolution and over the specific phase angles of OROCHI imaging (when landed), and comparing these near-field (<1 m) observations to remote (>5 km) spacecraft observations, we can prepare to interpret, and photometrically correct for, the phase angle dependence of the Phobos regolith spectral reflectance across the MMX sample area. This will also help prepare for the linking of remote sensing observations from the MMX spacecraft with the laboratory measurements of the Phobos samples that MMX will return to Earth in the 2030’s [9].

[1] Kuramoto et al, 2022, EPS, doi:10.1186/s40623-021-01545-7; [2] Kameda et al, 2021, EPS, doi: 10.1186/s40623-021-01462-9; [3] Stabbins & Kameda, 2026, PEPS, doi: 10.1186/s40645-025-00783-7; [4] Hirota et al, 2026, JpGU-AGU 2026; [5] Hirota et al, 2026, AOGS2026; [6] Golish et al, 2021, Icarus, doi: 10.1016/j.icarus.2020.113724; [7] Tatsumi et al, 2020, A&A, doi:10.1051/0004-6361/201937096; [9] Munaretto et al, 2025, A&A, doi:10.1051/0004-6361/202555720; [9] Tahara et al, 2025, MAPS, doi:10.1111/maps.70066;