Possible Closed-System Pingos in Utopia Planitia, Mars

Post by Dr. Richard Soare, Geography Department, Dawson College, Montreal, QC H3Z 1A4, Canada.

On Earth, hydrostatic or closed-system pingos (CSPs) are perennial ice-cored mounds formed by the freeze-thaw cycling of water when or as thermokarst lakes lose their water by drainage or evaporation. The mounds vary in shape from circular or sub-circular to elongate, are sub-kilometer in their long axes and may reach decameters in height. Some mounds show summit depressions, radial fractures and tiers. As the CSPs degrade, small-scale debris flows or slumps may occur; end-stage degradation often is marked by debris-laden ramparts elevated symmetrically or asymmetrically above the surrounding terrain. The presence of closed-system pingos on Mars might thus inform us about the planets’ past and/or present hydrologic conditions (Image 1).

Fig. 1

Image 1: Candidate closed-system pingos (CSPs) at the mid latitudes of Utopia Planitia, Mars
(HiRISE image ESP 027650_2275). Note the location of the potentially ice-cored mounds in polygonised thermokarst-like depressions and the interesting mound morphologies. On Earth, CSPs form almost uniquely in the midst of drained or water-depleted thermokarst lakes (alases) that are nested in ice-rich terrain. On Mars, we propose that the depressions form by the sublimation-driven loss of near-surface ice; this would also be the principal driver of ice-core depletion and/or collapse. Mounds 1-4 exhibit circular shapes and summit depressions that are commonplace amongst CSPs in regions like the Tuktoyaktuk Coastlands of northern Canada. The crescentic shape of Mound 5 could be a marker of mound collapse and the deflation/sublimation of a near-surface ice core, the geological buttress of pingo topography on Earth.

Typically, the CSPs originate and develop where deep and continuous permafrost is ice-rich, i.e. infused with excess ice, as it is in the Tuktoyaktuk Coastlands of northern Canada (Image 2), mid to northern Alaska and northeast Russia. The terrain in these regions comprises:

  1. a) thermokarst lakes and alases, i.e. thermokarst lake basins absent of water;
  2. b) small-scale ice-wedge polygons, showing either low-centers or high-centers relative to the (aggrading or degrading) polygon margins); and,
  3. c) meltwater filled or emptied polygon-margin troughs; if they are filled by meltwater and are interconnected they comprise beaded-stream networks.
Fig. 2a-g

Image 2: Closed-system pingos (CSPs) on Mars (candidates) and on Earth (actual). (a) Three
candidate CSPs on the floor of a thermokarst-like and polygonised, rimless depression. The adjacent terrain is mantled and not polygonised (HiRISE image ESP_055038_2250). (b) Close-up of the mounds in panel a. Note the irregularly-shaped summit depressions and geometries. (c) Candidate CSP on the floor of a thermokarst-like and polygonised depression. The adjacent terrain is polygonised but shows no mantling (HiRISE image ESP_044042_2240). (d) Close-up of the mound in panel c. Note the irregular topography of the summit and adjacent slopes as well as the small-scale pitting of the terrain surrounding terrain. (e) Candidate CSP in topographically uneven and polygonised terrain (HiRISE image ESP_026556_2245). (f) Same candidate CSP, showing domed mound-summit and diametrical crack that intercepts the polygonised terrain in which the mound has formed. Image credits (a-f): NASA/JPL/University of Arizona. (g) Split (bottom-centre) and Ibyuk (right) pingos in a thermokarst/ice-wedge complex, i.e. the Pingo Canadian Landmark (Tuktoyaktuk Coastlands, Northwest Territories, Canada). Each of these pingos exhibit summit depressions, radial fracturing and nesting within a thermokarst lake. Note the benched and unnamed peninsula-shaped pingo at the top left-hand corner of the image. Image credit: DigitalGlobe, GoogleEarth.

At the mid-latitudes of Utopia Planitia (UP) (~35-50o N; ~80-115o E) multiple candidate CSPs are observed (Images 2 and 3). The morphologies, scale and height of the Martian mounds, as well as the surface characteristics and spatially-associated landscape features or landforms, would be expected were the candidate mounds observed in ice-rich and CSP-populated regions on Earth.

Soare_UPMounds_overview_v4_PGIOTM

Image 3: Map of Utopia Planitia study area showing candidate closed-system pingo (CSP) locations with colour-coded elevations from the Mars Orbiter Laser Altimeter (MOLA). The background comprises a THEMIS day IR mosaic from the U.S. Geological Survey. Inset is the MOLA hill-shaded relief map showing the global location of the study area.

The mounds are nested in or reside adjacent to: flat-floored, sometimes tiered and rimless thermokarst-like depressions; small-scale polygons (some of which exhibit low or high centres relative to their margins, perhaps indicative of aggraded or degraded ice-wedges at the margins); and, connected (metre-scale) polygon-margin depressions that mirror beaded-stream systems in terrestrial periglacial regions. The size-frequency distribution of craters in our study region precludes a surface younger than ~100 Ma. This suggests that the CSP-like mounds and the possible periglacial-revisions of the adjacent/proximal landscapes may be less recent and somewhat older than had been thought. This relative age-dating is in line with Mars global climate-change models. The latter suggest that on a kilometre-scale the freeze-thaw cycling of surface and near-surface water is unlikely to have occurred in the very late (if not the current period of the) late Amazonian Epoch.

Further reading

Burr, D.M., Soare, R.J., Wan-Bun Tseung, J.M., Emery, J.P., 2005. Young (late Amazonian) near-surface ground-ice features near the equator. Icarus 178, 1, 56-73.

De Pablo, M.A., Komatsu, G., 2009. Possible pingo fields in the Utopia basin, Mars: Geological and climatical implications. Icarus 199, 1, 49-74.

Dundas, C.M., McEwen, A.S., 2010. An assessment of evidence for pingos on Mars using HiRISE. Icarus 205, 244-258.

Dundas, C.M., Mellon, M.T., McEwen, A.S., Lefort, A., Keszthelyi, L.P., Thomas, N., 2008. HiRISE observations of fractured mounds: Possible martian pingos. Geophysical Research Letters 35, L04201.

Harris, S.A., French, H.M., Heginbottom, J.A., Johnston, G.H., Ladanyi, B., Dego, D.C., van Everingen, R.O., 1988. Technical Memorandum. 142, Permafrost Subcommittee, National Research Council, 154 p.

Mackay, J.R., 1998. Pingo growth and collapse, Tuktoyaktuk Peninsula areas, western arctic coast, Canada: a long-term field study. Géographie physique et Quaternaire 52, 3, 1-53.

Mackay, J.R., 1999. Periglacial features developed on the exposed lake bottoms of seven lakes that drained rapidly after 1950, Tuktoyaktuk Peninsula Area, western arctic coast, Canada. Permafrost and Periglacial Processes. 10, 39-63.

Rampton, V.N., 1988. Quaternary geology of the Tuktoyaktuk Coastlands, Northwest Territories, Geological Society of Canada, Memoir 423, 98 p.

Samsonov, S.V., Lantz, T.C., Kokelj, S.V., Zhang, Y., 2016. Growth of a young pingo in the Canadian arctic observed by RADARSAT-2 interferometric satellite radar. Cryosphere 10, 799-810.

Schirrmeister, L., Siegert, C., Kunitzky, V.V., Grootes, P.M., Erlenkeuser, H., 2002. Late Quaternary ice-rich permafrost sequences as a paleoenvironmental archive for the Laptev Sea Region is northern Siberia. International Journal of Earth Sciences 91, 154-167.

Soare, R.J., Burr, D.M., Wan Bun Tseung, J-M., 2005. Pingos and a possible periglacial landscape in northwest Utopia Planitia, Mars. Icarus 174, 373-382.

Soare, R.J., Conway, S.J, Pearce, G., Dohm, J.M., Grindrod, P.M., 2013. Possible crater-based pingos, paleolakes and periglacial landscapes in the high latitudes of Utopia Planitia, Mars. Icarus, 225, 2, 971-981.

Soare, R.J., Conway, S.J., Dohm, J.M., El-Maarry, M.R., 2014. Possible open-system pingos in and around the Argyre impact basin, Mars. Earth and Planetary Science Letters 398, 25-36.

Soare, R.J., Conway, S.J., Gallagher, C., McKeown, L.E. 2019, in press. Possible (closed system) pingo and ice-wedge/thermokarst complexes at the mid latitudes of Utopia Planitia, Mars. Icarus.

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