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The construction of Chasma Boreale on Mars



The polar layered deposits of Mars contain the planet’s largest known reservoir of water ice1,2 and the prospect of revealing a detailed Martian palaeoclimate record3,4, but the mechanisms responsible for the formation of the dominant features of the north polar layered deposits (NPLD) are unclear, despite decades of debate. Stratigraphic analyses of the exposed portions of Chasma Boreale—a large canyon 500 km long, up to 100 km wide, and nearly 2 km deep—have led most researchers to favour an erosional process for its formation following initial NPLD accumulation. Candidate mechanisms include the catastrophic outburst of water5, protracted basal melting6, erosional undercutting7, aeolian downcutting7,8,9 and a combination of these processes10. Here we use new data from the Mars Reconnaissance Orbiter to show that Chasma Boreale is instead a long-lived, complex feature resulting primarily from non-uniform accumulation of the NPLD. The initial valley that later became Chasma Boreale was matched by a second, equally large valley that was completely filled in by subsequent deposition, leaving no evidence on the surface to indicate its former presence. We further demonstrate that topography existing before the NPLD began accumulating influenced successive episodes of deposition and erosion, resulting in most of the present-day topography. Long-term and large-scale patterns of mass balance achieved through sedimentary processes, rather than catastrophic events, ice flow or highly focused erosion, have produced the largest geomorphic anomaly in the north polar ice of Mars.

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Figure 1: Maps of Planum Boreum surface and depositional/erosional history.
Figure 2: SHARAD data and interpretation.
Figure 3: HiRISE image PSP_009914_2750 showing depositional relationship between NPLD and basal unit.
Figure 4: Cross-sectional illustration of hypothesized sequence of events leading to the development of Chasma Boreale and Gemina Lingula.

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We thank P. Choudhary for assistance with radar data analysis. Work at the University of Texas was supported by the Institute for Geophysics of the Jackson School of Geosciences, a NASA grant (NAG5-12693) to J.W.H. and a Mars Reconnaissance Orbiter (MRO) Participating Scientist grant to J.W.H. MRO is operated for NASA by Caltech’s Jet Propulsion Laboratory. SHARAD was provided to MRO by the Italian Space Agency through a contract with Thales Alenia Space Italia, and is operated by the INFOCOM Department, University of Rome. We thank the SHARAD Operations Center in Rome for their critical support. We honour the memory of our co-author and colleague A.S. This is UTIG contribution number 2186.

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Authors and Affiliations



J.W.H. initiated and led the SHARAD analysis effort, synthesized results and wrote the manuscript. K.E.F. and S.B. led HiRISE analysis, contributed material for early manuscript drafts and assisted in the final manuscript. S.C. assimilated SHARAD data and performed most of the radar mapping. A.S. provided focused and depth-corrected SHARAD data. K.T., K.E.H. and P.S.R. contributed to the HiRISE analysis and the manuscript. N.E.P. and R.J.P. provided radar validation and contributed to the manuscript.

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Correspondence to J. W. Holt.

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The authors declare no competing financial interests.

Additional information

Data from MRO, including SHARAD and HiRISE, are available at NASA’s Planetary Data System (

Supplementary information

Supplementary Information

This file contains Supplementary Notes A-E comprising: Initial NPLD deposition; PLD1/PLD2 contact mapping; Data coverage for grids; PLD1 thickness; Lower GL/CB radar stratigraphy and Supplementary Figures S1-S5 with legends. (PDF 1353 kb)

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Holt, J., Fishbaugh, K., Byrne, S. et al. The construction of Chasma Boreale on Mars. Nature 465, 446–449 (2010).

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