MMX geodesy investigations: science requirements and observation strategy

Koji Matsumoto,Noriyuki Namiki,Hideaki Miyamoto,Nicola Baresi,Hitoshi Ikeda,Shunichi Kamata,Hiroshi Araki,Akito Araya,Hiroki Senshu,Naru Hirata,Toru Kouyama,Keiko Yamamoto,Hirotomo Noda

doi:10.1186/s40623-021-01500-6

Abstract

In order to investigate the origin of Phobos and Deimos, the Japanese Martian Moons eXploration (MMX) mission is scheduled for launch in 2024. MMX will make comprehensive remote-sensing measurements of both moons and return regolith samples from Phobos to Earth. Geodetic measurements of gravity, shape, and rotation parameter of a body provides constraints on its internal structure reflecting its origin and evolution. Moments of inertia are important parameters to constrain the internal mass distribution, but they have not been well determined for the Martian moons yet. We discuss the mission requirements related to the moments of inertia to detect a potential heterogeneity of the mass distribution inside Phobos. We introduce mission instruments and operational strategies to meet the mission requirements. We present a preliminary imaging strategy from a quasi-satellite orbit for a base shape model that is expected to be created at the early stage of the mission. Geodetic products including ephemeris, gravity field, rotation parameter of Phobos, and spacecraft orbit are of importance not only for the geodetic study, but also for interpreting data from various mission instruments and selecting possible landing sites.Graphical

Highlights

The origin of Phobos is still an open issue
It is expected that the low density (∼ 1847 kg/ m3, "Bulk density and moments of inertia" section) of Phobos is due to the presence of significant macro-porosity and/or water ice in its interior, in both cases the distribution depends on the formation scenario
If the orbit determination process can estimate the spacecraft state, gravity field, rotation parameters, and camera pointing directions, the shape modeling results will be improved by these information, which will in turn update the orbit determination results by iterative procedures

Summary

Introduction

The origin of Phobos is still an open issue. It may either be a captured asteroid or have formed from a disk of impact ejecta produced by a giant impact (CraddockMatsumoto et al Earth, Planets and Space (2021) 73:2262011). The value of Lainey et al (2021) is close to that of Burmeister et al (2018), Mission requirements for MMX geodetic study the libration amplitude of Burmeister et al (2018) is consistent with that calculated using a Phobos shape model assuming a uniform density or homogenous internal structure (Willner et al 2014), possible heterogeneous interiors include layered structures with homothetic boundary shape to the surface because such structures give the same dynamical flattening γ and do not change the libration amplitude.

Results

Conclusion