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

Tomohiro Usui, Ken ichi Bajo, Wataru Fujiya, Yoshihiro Furukawa, Mizuho Koike, Yayoi N. Miura, Haruna Sugahara, Shogo Tachibana, Yoshinori Takano, Kiyoshi Kuramoto

Research output: Contribution to journalReview articlepeer-review

44 Citations (Scopus)


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, 13C/12C, 15N/14N) 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.

Original languageEnglish
Article number49
JournalSpace Science Reviews
Issue number4
Publication statusPublished - 2020 Jun 1


  • Endogenous Phobos material
  • Mars-originating materials
  • Martian Moons eXploration
  • Origin of Martian moons
  • Phobos sample return

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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