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

• Published in: Space science reviews 2020-06, Vol.216 (4), Article 49
• Main Authors: Usui, Tomohiro, Bajo, Ken-ichi, Fujiya, Wataru, Furukawa, Yoshihiro, Koike, Mizuho, Miura, Yayoi N., Sugahara, Haruna, Tachibana, Shogo, Takano, Yoshinori, Kuramoto, Kiyoshi
• Format: Article
• Language: English
• Subjects: Aerospace Technology and Astronautics; Asteroids; Astrophysics and Astroparticles; Composition; Deimos; Dust particles; Ejecta; Flyby missions; Interplanetary dust; Isotope composition; Japanese space program; Mars; Mars dust; Mars satellites; Mineralogy; Moon; Nitrogen isotopes; Organic materials; Outer solar system; Phobos; Physics; Physics and Astronomy; Planetology; Projectiles; Radiometric dating; Regolith; Remote sensing; Role of Sample Return in Addressing Major Questions in Planetary Sciences; Sample return missions; Solar system; Space exploration; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Spacecraft; Systematics; Terrestrial planets; Voyager 1 spacecraft
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-020-00668-9

Phobos and Deimos occupy unique positions both scientifically and programmatically on the road to the exploration of the solar system. Japan Aerospace Exploration Agency (JAXA) plans a Phobos sample return mission (MMX: Martian Moons eXploration). The MMX spacecraft is scheduled to be launched in 2024, orbit both Phobos and Deimos (multiple flybys), and retrieve and return >10 g of Phobos regolith back to Earth in 2029. The Phobos regolith represents a mixture of endogenous Phobos building blocks and exogenous materials that contain solar system projectiles (e.g., interplanetary dust particles and coarser materials) and ejecta from Mars and Deimos. Under the condition that the representativeness of the sampling site(s) is guaranteed by remote sensing observations in the geologic context of Phobos, laboratory analysis (e.g., mineralogy, bulk composition, O-Cr-Ti isotopic systematics, and radiometric dating) of the returned sample will provide crucial information about the moon’s origin: capture of an asteroid or in-situ formation by a giant impact. If Phobos proves to be a captured object, isotopic compositions of volatile elements (e.g., D/H, 13 C/ 12 C, 15 N/ 14 N) in inorganic and organic materials will shed light on both organic-mineral-water/ice interactions in a primitive rocky body originally formed in the outer solar system and the delivery process of water and organics into the inner rocky planets.