Fate of an Earth‐Like Water Inventory on Mars

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Abstract

We have determined the global inventory of surface and near‐surface water on Mars by tracking the amounts of water lost to each of the significant sinks for water. The sinks include loss to space, formation of hydrated minerals, possible remnants of an ancient ocean, water present within the crust, and the present‐day polar caps and near‐surface ice deposits; we utilize both previous analyses and new analyses of the amount of water in the sinks. Summed up, they total 380–970 m H ₂O (as a global equivalent layer), and possibly up to 685–1,970 m if possible crustal liquid water or ice is included. For comparison, the Earth's surface and near‐surface inventory, scaled to Mars, would be 1,400 m. This value for an Earth‐like Mars falls within the range of possible values for Mars, suggesting that Mars had a similar surface inventory of surface and near‐surface water. This abundance of water on early Mars is able to produce the observed water‐related geological features and suggests the presence of an early habitable environment capable of supporting life.

Plain Language Summary

We have examined the sinks for water (i.e., where the water has gone) to determine how much water has been on Mars. By quantifying how much water has gone into each sink, we can estimate the total amount of water that Mars had. Our results suggest that Mars had between 380 and 1,970 m of water, expressed as the thickness of a layer of water on the surface, had it all been present there at one time. This amount of water can explain the observed water‐related geological features, and points to a planet that could have sustained life early in its history.

Key Points

We have determined the inventory of water on Mars by quantifying the observeable sinks for water
The sinks add up to there having been 380–1,970 m of water (as a global equivalent layer)
This amount of water would have been able to produce the observed geological features and indicates a planet conducive to having had life

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Most cited references 86

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A habitable fluvio-lacustrine environment at Yellowknife Bay, Gale crater, Mars.

J P Grotzinger, D Y Sumner, L. C. Kah … (2014)

The Curiosity rover discovered fine-grained sedimentary rocks, which are inferred to represent an ancient lake and preserve evidence of an environment that would have been suited to support a martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. Carbon, hydrogen, oxygen, sulfur, nitrogen, and phosphorus were measured directly as key biogenic elements; by inference, phosphorus is assumed to have been available. The environment probably had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial-lacustrine environments in the post-Noachian history of Mars.

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Hydrated silicate minerals on Mars observed by the Mars Reconnaissance Orbiter CRISM instrument.

John F Mustard, S L Murchie, S M Pelkey … (2008)

Phyllosilicates, a class of hydrous mineral first definitively identified on Mars by the OMEGA (Observatoire pour la Mineralogie, L'Eau, les Glaces et l'Activitié) instrument, preserve a record of the interaction of water with rocks on Mars. Global mapping showed that phyllosilicates are widespread but are apparently restricted to ancient terrains and a relatively narrow range of mineralogy (Fe/Mg and Al smectite clays). This was interpreted to indicate that phyllosilicate formation occurred during the Noachian (the earliest geological era of Mars), and that the conditions necessary for phyllosilicate formation (moderate to high pH and high water activity) were specific to surface environments during the earliest era of Mars's history. Here we report results from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) of phyllosilicate-rich regions. We expand the diversity of phyllosilicate mineralogy with the identification of kaolinite, chlorite and illite or muscovite, and a new class of hydrated silicate (hydrated silica). We observe diverse Fe/Mg-OH phyllosilicates and find that smectites such as nontronite and saponite are the most common, but chlorites are also present in some locations. Stratigraphic relationships in the Nili Fossae region show olivine-rich materials overlying phyllosilicate-bearing units, indicating the cessation of aqueous alteration before emplacement of the olivine-bearing unit. Hundreds of detections of Fe/Mg phyllosilicate in rims, ejecta and central peaks of craters in the southern highland Noachian cratered terrain indicate excavation of altered crust from depth. We also find phyllosilicate in sedimentary deposits clearly laid by water. These results point to a rich diversity of Noachian environments conducive to habitability.