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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

 

日本語の解説記事

火星に新しい水素の貯蔵庫を発見 ―火星の海はどこへ消えたのか?―

 

Reference:

Usui, T., Alexander, C.M.O'D., Wang J., Simon, J.I. and Jones, J.H.

Meteoriticevidence for a previously unrecognized hydrogen reservoir on Mars,

Earth and Planetary Science Letters, 410, 140-151 (2015)

 


  Caption: Schematic cross sections illustrating locations of the Martian water reservoirs based on our ground ice model (Usui et al. 2015).  The intermediate-δD water/ice reservoir occurs as ground-ice deposits interbedded within sediments in the northern lowlands.  This model requires limited interaction between the buried water/ice reservoirs and the atmosphere (shown as dashed arrows).