Aqua Planetology

  • High resolution and dense datasets of Martian surface has raised an issue; is current Martian cryosphere local or global? Trying to solve this issue, we are surveying underground structure using subsurface radar data.

    [Official website]

    Origin of water on Mars

    The sculpted channels of the Martian southern hemisphere speak loudly of flowing water, but this terrain is ancient. Consequently, planetary scientists often describe early Mars as ‘warm and wet’ and current Mars as ‘cold and dry’. However, despite its crucial role in biological and geological processes, information about water on Mars is still controversial.

    We (Tomohiro Usui and his collaborators at NASA’s Johnson Space Center and Carnegie Institute of Washington) report on geochemical studies that help towards settling the controversy that surrounds the origin, abundance, and history of water on Mars. The team reveals the micro-distribution of hydrogen isotopes recorded in Martian meteorites; hydrogen is the major component of water and it isotopes (H and Deuterium) are good indicators to trace the history of water. We report definitive evidence that the Martian mantle has retained a primordial hydrogen isotope composition similar to water on Earth but distinct from the water in the present Martian atmosphere.

    These observations suggest that Mars and Earth should have similar water sources probably originated from the Main-belt asteroids, and that Mars should have experienced significant atmospheric loss through the history, which induced the climate change from ‘warm and wet’ to ‘cold and dry’.

    More information: [NASA Press release on November 19, 2012]

    Evolution of surface water on Mars

    Martian surface morphology implies that Mars was once warm enough to maintain persistent liquid water on its surface. While the high D/H ratios (~5000 per mil) of the current martian atmosphere suggest that significant water has been lost from the surface during the martian history, the timing, the processes, and the amount of the water loss have been poorly constrained. Recent technical developments of ion-microprobe analysis of Martian meteorites have provided accurate estimation of hydrogen isotope compositions (D/H) of Martian water reservoirs at the time when the meteorites formed. Based on the D/H datasets from Martian meteorites, we estimate the amounts of water loss due to atmospheric escape and demonstrate that water loss during pre-Noachian was more significant than in the rest of the martian history. Combining our results with geological and geomorphological evidence for ancient oceans, we propose a possibility that there should be undetected subsurface water/ice of much greater extent than the collective amounts of “visible” current water inventory. Our study further implies that, because such large water inventory automatically calls for significant water loss that cannot be explained by oxygen escape models, unknown mechanisms that effectively consume the remaining excess oxygen should be required.

    More information: [Inside Science on May23, 2015]

    Evidence of subsurface water on Mars

    The surface geology and geomorphology of Mars indicates that it was once warm enough to maintain a large body of liquid water on its surface, though such a warm environment might have been transient. The transition to the present cold and dry Mars is closely linked to the history of surface water, yet the evolution of surficial water is poorly constrained.

    We have conducted in situ hydrogen isotope (D/H) analyses of quenched and impact glasses in three Martian meteorites (Yamato 980459, EETA79001, LAR 06319). The hydrogen isotope analyses provide evidence for the existence of a distinct but ubiquitous water/ice reservoir (D/H = 2–3 times Earth’s ocean water: SMOW) that lasted from at least the time when the meteorites crystallized (173–472 Ma) to the time they were ejected by impacts (0.7–3.3 Ma), but possibly much longer. The origin of this reservoir appears to predate the current Martian atmospheric water (D/H = ~5–6×SMOW) and is unlikely to be a simple mixture of atmospheric and primordial water retained in the Martian mantle (D/H ≈SMOW). Given the fact that this intermediate-D/H reservoir (2–3×SMOW) is observed in a diverse range of Martian materials with different ages (SNC meteorites, ALH 84001, Curiosity surface data), we conclude that this intermediate-D/H reservoir is likely a global surficial feature that has remained relatively intact over geologic time. We propose that this reservoir represents either hydrated crust and/or ground ice interbedded within sediments. Our results corroborate the hypothesis that a buried cryosphere accounts for a large part of the initial water budget of Mars.

    More information: [NASA Press release on December 18, 2014]


  • Hayabusa2 spacecraft explored the C-type asteroid Ryugu, which is expected to contain water and organics as building blocks of the Earth. Hayabusa2 mission aims to reveal the origin of the primitive asteroid, oceans on the Earth, and where do we come from.

    [Official website]

    Curation and initial analyses of Hayabusa-2 samples

  • The samples from C-type asteroid Ryugu will be returned to ISAS on December 2020. We manage the chamber dedicated to Ryugu samples including infrared hyperspectral microscope (MicrOmega). After the initial description and characterization of samples, we will conduct the analyses consisted with the detailed petrologic observation, spectral measurements, and inorganic and organic chemical measurements etc.

    (Member: Tomohiro Usui, Haruna Sugahara, Moe Matsuoka, Ryota Fukai)


  • Martian Moons eXploration (MMX); a sample-return mission to clarify the origin of Mars and Martian moons, Phobos and Deimos. (Image credit: JAXA)

    The big picture of MMX is to understand the origin and evolution process of our habitable solar system. The targets of MMX, Phobos and Deimos, are possibly formed by (i) a captured asteroid after Mars formation, or (ii) scattered fragments made by a giant impact. The formation process will be determined after moon observations and returned sample analyses. MMX will also reveal the mechanism of atmospheric material circulation and dispersion based on observation results of Mars and its surrounding space from the vicinity of Martian moon.

    [Official website]

  • It is indicated that small impacts on Mars throughout its history delivered impact ejecta from Mars to Phobos and Deimos. Recent study shows that the total amount of the delivery of Mars ejecta to Phobos and Deimos is 10-100 times larger than previously estimated and Mars ejecta mixed in the regolith of its moons potentially covers all its geological eras and consists of all types of rocks, from sedimentary to igneous. MMX would sample such diverse Mars materials back to the Earth. The study of the moons opens the door to looking at more than individual objects but at the Mars System Science.

    [Recent study]

    Field Trip Report

  • Lava rock sampling @Izu Peninsula

    On April 14, 2019, we went to the Funabara quarry (Izu City, Shizuoka) to collect lava rock samples for a laboratory experiment conducted by R. Noguchi.

    [Read more]