The recurring slope lineae on Mars have been hypothesized to originate from snow melting, deliquescence, dry flow or shallow groundwater. Except for the dry flow origin, these hypotheses imply the presence of surficial or near-surface volatiles, placing the exploration and characterization of potential habitable environments within the reach of existing technology. Here we present observations from the High Resolution Imaging Science Experiment, heat-flow modelling and terrestrial analogues, which indicate that the source of recurring slope lineae could be natural discharge along geological structures from briny aquifers within the cryosphere, at depths of approximately 750 m. Spatial correlation between recurring slope lineae source regions and multi-scale fractures (such as joints and faults) in the southern mid-latitudes and in Valles Marineris suggests that recurring slope lineae preferably emanate from tectonic and impact-related fractures. We suggest that deep groundwater occasionally surfaces on Mars in present-day conditions.
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McEwen, A. S. et al. Seasonal flows on warm Martian slopes. Science 333, 740–743 (2011).
McEwen, A. S. et al. Recurring slope lineae in equatorial regions of Mars. Nat. Geosci. 7, 53–58 (2014).
Ojha, L. et al. Spectral evidence for hydrated salts in recurring slope lineae on Mars. Nat. Geosci. 8, 829–832 (2015).
Martinez, G. M. & Renno, N. O. Water and brines on Mars: current evidence and implications for MSL. Space Sci. Rev. 175, 29–51 (2013).
Chevrier, V. F. & Rivera-Valentin, E. G. Formation of recurring slope lineae by liquid brines on present-day Mars. Geophys. Res. Lett. 39, L21202 (2012).
Stillman, D. E., Michaels, T. I., Grimm, R. E. & Hanley, J. Observations and modeling of northern mid-latitude recurring slope lineae (RSL) suggest recharge by a present-day Martian briny aquifer. Icarus 265, 125–138 (2016).
Heinz, J., Schulze‐Makuch, D. & Kounaves, S. P. Deliquescence‐induced wetting and RSL‐like darkening of a Mars analogue soil containing various perchlorate and chloride salts. Geophys. Res. Lett. 43, 4880–4884 (2016).
Massé, M. et al. Transport processes induced by metastable boiling water under Martian surface conditions. Nat. Geosci. 9, 425–428 (2016).
Schmidt, F., Andrieu, F., Costard, F., Kocifaj, M. & Meresescu, A. G. Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows. Nat. Geosci. 10, 270–273 (2017).
Heldmann, J. L. & Mellon, M. T. Observations of Martian gullies and constraints on potential formation mechanisms. Icarus 168, 285–304 (2004).
Heldmann, J. L. et al. Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions. J. Geophys. Res. 110, E05004 (2005).
Stillman, D. E., Michaels, T. I. & Grimm, R. E. Characteristics of the numerous and widespread recurring slope lineae (RSL) in Valles Marineris, Mars. Icarus 285, 195–210 (2017).
Farrell, W. M. et al. Is the Martian water table hidden from radar view? Geophys. Res. Lett. 36, L15206 (2009).
Nunes, D. C. et al. Examination of gully sites on Mars with the shallow radar. J. Geophys. Res. 115, E10004 (2010).
Heggy, E. et al. On water detection in the martian subsurface using sounding radar. Icarus 154, 244–257 (2001).
Heggy, E. et al. Ground penetrating radar sounding in mafic lava flows: Assessing attenuation and scattering losses in Mars analog volcanic terrains. J. Geophys. Res. 111, E06S04 (2006).
Orosei, R. et al. Radar evidence of subglacial liquid water on Mars. Science 361, 490–493 (2018).
Kumar, P. S. & Kring, D. A. Impact fracturing and structural modification of sedimentary rocks at Meteor Crater, Arizona. J. Geophys. Res. 113, E09009 (2008).
Kumar, P. S., Head, J. W. & Kring, D. A. Erosional modification and gully formation at Meteor Crater, Arizona: insights into crater degradation processes on Mars. Icarus 208, 608–620 (2010).
Singhal, B. B. S. & Gupta, R. P. in Applied Hydrogeology of Fractured Rocks (Springer Science & Business Media, 2010).
Andrews‐Hanna, J. C., Zuber, M. T. & Hauck, S. A. Strike‐slip faults on Mars: observations and implications for global tectonics and geodynamics. J. Geophys. Res. 113, E08002 (2008).
Montgomery, D. R. et al. Continental-scale salt tectonics on Mars and the origin of Valles Marineris and associated outflow channels. Geol. Soc. Am. Bull. 121, 117–133 (2009).
Treiman, A. H. Ancient groundwater flow in the Valles Marineris on Mars inferred from fault trace ridges. Nat. Geosci. 1, 181–183 (2008).
Montgomery, D. R. & Gillespie, A. Formation of Martian outflow channels by catastrophic dewatering of evaporite deposits. Geology 33, 625–628 (2005).
Marra, W. A., Braat, L., Baar, A. W. & Kleinhans, M. G. Valley formation by groundwater seepage, pressurized groundwater outbursts and crater-lake overflow in flume experiments with implications for Mars. Icarus 232, 97–117 (2014).
Osinski, G. R. & Lee, P. Intra‐crater sedimentary deposits at the Haughton impact structure, Devon Island, Canadian High Arctic. Meteorit. Planet. Sci. 40, 1887–1899 (2005).
Osinski, G. R. & Spray, J. G. Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic. Meteorit. Planet. Sci. 40, 1813–1834 (2005).
Carr, M. H. Formation of Martian flood features by release of water from confined aquifers. J. Geophys. Res. 84, 2995–3007 (1979).
Gaidos, E. J. Cryovolcanism and the recent flow of liquid water on Mars. Icarus 153, 218–223 (2001).
Mellon, M. T. & Phillips, R. J. Recent gullies on Mars and the source of liquid water. J. Geophys. Res. 106, 23165–23179 (2001).
Hauber, E. et al. Asynchronous formation of Hesperian and Amazonian aged deltas on Mars and implications for climate. J. Geophys. Res. 118, 1529–1544 (2013).
Scheidegger, J. M., Bense, V. F. & Grasby, S. E. Transient nature of Arctic spring systems driven by subglacial meltwater. Geophys. Res. Lett. 39, L12405 (2012).
Pope, K. O., Rejmankova, E. & Paris, J. F. Spaceborne imaging radar-C (SIR-C) observations of groundwater discharge and wetlands associated with the Chicxulub impact crater, northwestern Yucatan Peninsula, Mexico. Geol. Soc. Am. Bull. 113, 403–416 (2001).
Komatsu, G. et al. Drainage systems of Lonar Crater, India: contributions to Lonar Lake hydrology and crater degradation. Planet. Space Sci. 95, 45–55 (2014).
Abotalib, A. Z., Sultan, M. & Elkadiri, R. Groundwater processes in Saharan Africa: implications for landscape evolution in arid environments. Earth Sci. Rev. 156, 108–136 (2016).
Andersen, D. T., Pollard, W. H., McKay, C. P. & Heldmann, J. Cold springs in permafrost on Earth and Mars. J. Geophys. Res. 107, 5015 (2002).
Forte, E., Dalle Fratte, M., Azzaro, M. & Guglielmin, M. Pressurized brines in continental Antarctica as a possible analogue of Mars. Sci. Rep. 6, 33158 (2016).
Goldspiel, J. M. & Squyres, S. W. Groundwater discharge and gully formation on martian slopes. Icarus 211, 238–258 (2011).
Stillman, D. E., Michaels, T. I., Grimm, R. E. & Harrison, K. P. New observations of Martian southern mid-latitude recurring slope lineae (RSL) imply formation by freshwater subsurface flows. Icarus 233, 328–341 (2014).
Chojnacki, M. et al. Geologic context of recurring slope lineae in Melas and Coprates Chasmata, Mars. J. Geophys. Res. 121, 1204–1231 (2016).
Kirk, R. L. et al. Ultrahigh resolution topographic mapping of Mars with MRO HiRISE stereo images: Meter scale slopes of candidate Phoenix landing sites. J. Geophys. Res. 113, E00A24 (2008).
Clifford, S. M. A model for the hydrologic and climatic behavior of water on Mars. J. Geophys. Res. 98, 10973–11016 (1993).
Clifford, S. M. et al. Depth of the Martian cryosphere: revised estimates and implications for the existence and detection of subpermafrost groundwater. J. Geophys. Res. 115, E07001 (2010).
Levy, J. Hydrological characteristics of recurrent slope lineae on Mars: evidence for liquid flow through regolith and comparisons with Antarctic terrestrial analogs. Icarus 219, 1–4 (2012).
Archer, D. G. & Carter, R. W. Thermodynamic properties of the NaCl H2O system. 4. Heat capacities of H2O and NaCl (aq) in cold-stable and supercooled states. J. Phys. Chem. B 104, 8563–8584 (2000).
The authors are grateful to M. Sultan from Western Michigan University, R. Elkadiri from Middle Tennessee State University, H. El Safty from USC and Y. Gim from JPL for the discussions that helped to generate this manuscript. The first author is a postdoctoral research associate currently funded by the University of Southern California under the NASA Planetary Geology and Geophysics award NNX15AV76G awarded to the principal investigator E.H.
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