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Recurring slope lineae in equatorial regions of Mars


The presence of liquid water is a requirement of habitability on a planet. Possible indicators of liquid surface water on Mars include intermittent flow-like features observed on sloping terrains. These recurring slope lineae are narrow, dark markings on steep slopes that appear and incrementally lengthen during warm seasons on low-albedo surfaces. The lineae fade in cooler seasons and recur over multiple Mars years. Recurring slope lineae were initially reported to appear and lengthen at mid-latitudes in the late southern spring and summer and are more common on equator-facing slopes where and when the peak surface temperatures are higher. Here we report extensive activity of recurring slope lineae in equatorial regions of Mars, particularly in the deep canyons of Valles Marineris, from analysis of data acquired by the Mars Reconnaissance Orbiter. We observe the lineae to be most active in seasons when the slopes often face the sun. Expected peak temperatures suggest that activity may not depend solely on temperature. Although the origin of the recurring slope lineae remains an open question, our observations are consistent with intermittent flow of briny water. Such an origin suggests surprisingly abundant liquid water in some near-surface equatorial regions of Mars.

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Figure 1: Locations of confirmed recurring slope lineae (RSL).
Figure 2: Portion of Coprates Chasma showing RSL on generally north-facing slopes in northern summer and southern winter.
Figure 3: RSL on the south-facing slope of a crater on the floor of Melas Chasma.
Figure 4: Thermal model for the crater on the floor of Melas Chasma (11.5° S, 290.3° E).

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We thank the MRO and Mars Odyssey projects and science teams for returning a wealth of data, and we thank NASA for supporting extended mission science. P. R. Christensen provided constructive review comments. NASA’s MRO project and Mars Data Analysis Program supported this work.

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Authors and Affiliations



A.S.M. and C.M.D. planned many of the HiRISE observations to search for and monitor the equatorial RSL. Image analysis to locate and track candidate RSL was performed by A.S.M. with significant help from C.M.D. and L.O. S.S.M. led production of DTMs and orthorectified images. M.C. assisted with DTM production and measurements, RSL reconnaissance and image analysis. A.D.T. extracted column abundances of water vapour from the CRISM data. S.B. contributed the thermal analyses. S.L.M., J.J.W. and L.O. contributed to CRISM observations and compositional analyses. N.T. contributed photometric analyses. All authors contributed to discussions, interpretations and writing.

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Correspondence to Alfred S. McEwen.

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The authors declare no competing financial interests.

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McEwen, A., Dundas, C., Mattson, S. et al. Recurring slope lineae in equatorial regions of Mars. Nature Geosci 7, 53–58 (2014).

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