The landscape of the north polar layered deposits of Mars (NPLD) is dominated by a pinwheel array of enigmatic spiral troughs1. The troughs have intrigued planetary scientists since the Mariner 9 spacecraft returned the first close-up image in 1972, but conclusive evidence of their origin has remained elusive. Debate continues regarding all aspects of the troughs, including the possibility that they have migrated2, 3, 4, 5, their age in relation to the current NPLD surface6, and whether they are fundamentally erosional6, 7 or constructional2, 4 features. The troughs are probably related to climatic processes2, 8, yet the nature of this relationship has remained a mystery. Previous data characterizing only the exposed NLPD surface were insufficient to test these hypotheses. Here we show that the central spiral troughs initiated after deposition of three-quarters of the NPLD, quickly reached a stable morphology and migrated approximately 65 kilometres poleward and 600 metres in altitude over the past two million years or so. Our radar stratigraphy rules out hypotheses of erosional incision post-dating deposition6, 7, 9, 10, and instead largely validates an early hypothesis for constructional trough migration2, 3, 4, 5 with wind transport and atmospheric deposition as dominant processes. These results provide hard constraints for palaeo-climate models and a new context for evaluating imagery, spectral data, and now radar sounding data, the better to understand the link between orbital parameters and climate, the role of climate in shaping the polar ice of Mars, and eventually, the age of the polar deposits themselves8, 11, 12, 13.
At a glance
- Evolution of Martian polar landscapes—interplay of long-term variations in perennial ice cover and dust storm intensity. J. Geophys. Res. 84, 2975–2994 (1979) , &
- The evolution of dust deposits in the Martian north polar region. Icarus 40, 244–261 (1979)
- Origin of the stepped topography of the Martian poles. Icarus 34, 581–599 (1978)
- Stratigraphic relationships within Martian polar cap deposits. Icarus 50, 161–215 (1982) , &
- The role of eolian processes in forming surface features of the Martian polar layered deposits. Icarus 144, 267–288 (2000)
- North polar region of Mars: advances in stratigraphy, structure, and erosional modification. Icarus 196, 318–358 (2008) et al.
- Geologic history of the polar regions of Mars based on Mars Global Surveyor data. II. Amazonian period. Icarus 154, 22–39 (2001) &
- North polar cap of Mars: polar layered deposit characterization and identification of a fundamental climate signal. J. Geophys. Res. 110 doi:10.1029/2004JE002349 (2005) &
- How do spiral troughs form on Mars? Geology 32, 365–367 (2004)
- Evidence for ice flow prior to trough formation in the Martian north polar layered deposits. Icarus 195, 90–105 (2008) et al.
- Recent ice ages on Mars. Nature 426, 797–802 (2003) , , , &
- Origin and characteristics of the Mars north polar basal unit and implications for polar geologic history. Icarus 174, 444–474 (2005) &
- Models of climate cycles recorded in Martian polar layered deposits. Icarus 50, 216–244 (1982) &
- Wind erosion in the Martian polar region. J. Geophys. Res. 78 (20) 4211–4221 (1973)
- Mariner 9 observations of the surface of Mars in the north polar region. J. Geophys. Res. 78, 4197–4210 (1973) , , &
- Evidence of fractures in NPLD and their significance to the formation of Martian polar spiral troughs. 39th Lunar Planet. Sci. Conf. abstr. 2179 (Lunar and Planetary Institute, 2008) http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2179.pdf. et al.
- Patterning instability on the Mars polar ice caps. J. Geophys. Res. Planets 111, E02005 (2006) &
- Internal layers in an “accublation” ice cap: a test for flow. Icarus 144, 289–294 (2000)
- The polar spirals of Mars may be due to glacier surges deflected by Coriolis forces. Earth Planet. Sci. Lett. 76, 227–240 (1986)
- If Martian ice caps flow: ablation mechanisms and appearance. Icarus 105, 501–511 (1993)
- Radar soundings of the subsurface of Mars. Science 310, 1925–1928 (2005) et al.
- SHARAD sounding radar on the Mars Reconnaissance Orbiter. J. Geophys. Res. Planets 112, E05S05 (2007) et al.
- Mars north polar deposits: stratigraphy, age, and geodynamical response. Science 320, 1182–1185 (2008) et al.
- North polar deposits of Mars: extreme purity of the water ice. Geophys. Res. Lett. 36, L03203 (2009) et al.
- Radar subsurface mapping of the polar layered deposits on Mars. J. Geophys. Res. Planets 111, E06S21 (2006) &
- Martian south polar layered deposit stratigraphy and implications for accumulation history. J. Geophys. Res. Planets 113, E06007 (2008) &
- The construction of Chasma Boreale on Mars. Nature doi:10.1038/nature09050 (this issue) et al.
- Martian north polar layered deposits stratigraphy: implications for accumulation rates and flow. J. Geophys. Res. Planets 111, E06012 (2006) &
- Mars Orbiter Laser Altimeter: experiment summary after the first year of global mapping of Mars. J. Geophys. Res. Planets 106 doi:10.1029/2000JE001364 (2001) et al.
- THEMIS Public Data Releases. http://themis-data.asu.edu (Planetary Data System node, Arizona State University) , , &
- Supplementary Information (606K)
This file contains Supplementary Notes S1-S5, Supplementary Figures S1-S5 with legends and References.