Conway, S.

Dohm, J. M.

Pearce, G.

Soare, R. J.

English

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Open Research OnlineThe Open University’s repository of research publicationsand other research outputsPossible crater-based pingos, paleolakes and periglaciallandscapes in the high latitudes of Utopia Planitia,MarsConference or Workshop ItemHow to cite:Soare, R. J.; Pearce, G.; Conway, S. and Dohm, J. M. (2011). Possible crater-based pingos, paleolakes andperiglacial landscapes in the high latitudes of Utopia Planitia, Mars. In: Fifth International Conference on Mars PolarScience and Exploration, 12-16 Sep 2011, Fairbanks, Alaska, USA.For guidance on citations see FAQs.c© 2011 The AuthorsVersion: Not SetLink(s) to article on publisher’s website:http://www.lpi.usra.edu/meetings/polar2011/Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyrightowners. For more information on Open Research Online’s data policy on reuse of materials please consult the policiespage.oro.open.ac.ukPOSSIBLE CRATER-BASED PINGOS, PALEOLAKES AND PERIGLACIAL LANDSCAPES IN THE HIGH LATITUDES OF UTOPIA PLANITIA, MARS. R.J. Soare1, G. Pearce1, S. Conway2, J.M. Dohm3. 1Department of Geography, Dawson College, 3040 Sherbrooke St. West, Montreal, Canada H3Z 1A4 (rsoare@dawsoncollege.qc.ca); 2LPGN, CNRS/Univ. Nantes, 44322, Nantes, France (susan.conway@univ-nantes.fr); 3Department of Hydrology & Water Resources, Univ. of Arizona, USA (jmd@hwr.arizona.edu).   Introduction: On Earth, hydrostatic or closed pin-gos are perennially ice-cored mounds that are diagnos-tic of (a) ponded water (current or past); (b) freeze-thaw cycles; and, (c) ice-rich, continuous permafrost [1-2].           Figure 1: Assemblage of closed-pingos, Tuktoyak- tuk Coastlands, northern Canada. Thermokarst lakes en- velope the pingos; small-sized (and unsorted) polygonal pat-terned-ground is ubiquitous (air photo A2797-35-1993,  National Air Photo Library, Ottawa, Canada).  Similar environmental conditions could be deduced were closed pingos observed on Mars [3-9]. Moreover, if these landforms were to occur on very late Amazo-nian rock materials, this would point to relatively re-cent boundary conditions of temperature and atmos-pheric pressure that are higher than many workers have thought possible.  In 2005 we used a small set of MOC images to de-scribe two crater-floor landscapes in northern Utopia Planitia (UP) where mounds consistent in appearance, distribution and geological traits with closed pingos on Earth, at least those located in the Tuktoyaktuk Coast-lands (TC) of northern Canada, were observed [3-4]. Based on HiRISE and MOC images, (not available at the time of our earlier work) we revisit the closed pingo hypothesis and do two things. First, we broaden the scope of the pingo hypothesis by integrating the observations of four other crater-floor landscapes with similar mounds. Interestingly, each of these craters are located within a tight latitudinal band (64.5-68.90 N). Second, we link the atmospheric processes that could be responsible for the formation of crater-based peren-nial ice-domes at latitudes 70° N [10] to the em-placement of water-ice (and the subsequent formation of crater-based paleolakes) at the lower latitudes where the putative pingos have been observed.  Mound morphology and traits (Mars) (Fig. 2): The Martian crater-floor mounds are elongate to circu-lar/sub-circular; they range in diameter from tens to hundreds of metres and are clustered (2.5 mounds/km2) at or near the floor centres. A few of the mounds display a ring-like appearance. All of the mounds are nested in small-sized (25-150 m in di-ameter) polygonal patterned-ground that is unsorted. Some of the polygons exhibit an orthogonal orientation around the mounds; others, cross-cut the mounds.             Figure 2: Crater-floor mounds in a field of small-sized and un-sorted polygonal patterned-ground. El Maarry et al. [11] have sug-gested that the size, type and location of these polygons  could be indicative of endogenic paleolakes  (PSP_007780 _2450_RED, 64.5° N; 67.3° E).  Pingo morphology and traits (Earth):. Closed pingos range in shape from elongate to circular/sub-circular; diameters vary from a few to hundreds of metres. Often, as is the case in the TC, closed pingos occur in the midst of thermokarst lakes (extant or ex-tinct). Where summit collapse has occurs, the pingos may appear ring-like. Commonly, the mounds occur in consolidated networks of small-sized (25-75 m in diameter) and unsorted polygonal patterned-ground. Sometimes, these polygons cross-cut the mounds Pingo origin (Earth): In the TC, a region charac-terised by continuous and ice-rich permafrost, pingo genesis is tied closely to the loss of water by drainage or evaporation in thermokarst lakes [1]. As a thermo-karst lake loses its water, the exposure of saturated but previously unfrozen lake-floor sediments to new, colder boundary conditions induces these sediments to freeze (by permafrost aggradation); subsequently, the ground is deformed upwardly by means of hydrostatic pressure. Eventually, this forms a domed struc-ture/mound underlain by an ice core. Although unre-lated in origin, small-sized (thermal contraction) and unsorted polygonal patterned-ground is a common-300 m Beaufort Sea 300 m Utopia Planitia 6005.pdfFifth Mars Polar Science Conference (2011)place characteristic of permafrost terrain where closed pingos occur [1]. Polygonal patterned-ground that is orthogonal in orientation may develop when the loss of water in a lake basin where a pingo forms is episodic [13].  Closed pingos in UP?:The Martian mounds ap-proximate terrestrial closed-pingos (of the TC type) in size, shape, ring-like appearance (sometimes) and spa-tial association with unsorted and polygonal patterned-ground. Interestingly, the mounds show dense cluster-ing that is similar to that of the closed pingos in the TC; also, they are located at or near the centre of im-pact-crater floors, precisely where one would expect them to be on the basis of the TC model.  Crater-based paleolakes: All but two of the mound craters are included in a recent survey of puta-tive crater-based paleolakes [11]. The occurrence of these paleolakes is deduced from the polygon type found in these craters, which is consistent with a desic-cation origin [11]. Our craters occur within a narrow band of these paleolakes around the polar cap (Fig. 3).      Figure 3: Map of different crater types, north polar region, Mars.  Periglacial mound origin: Since 2005, the possi-bility that closed pingos could have formed in UP late in the Amazonian Period has been widely discussed in the literature [3-9]. As noted above, the origin and de-velopment of closed pingos requires a) the occurrence of near-surface ice-rich regolith; and, b) pre-cursor boundary conditions above the triple point of water. The first criteria can be met as near-surface ground ice is thought to be ubiquitous throughout the high north-ern-latitudes [14-15]; the origin and/or recharge of ground-ice at these latitudes could be supplied by wa-ter-vapour laden winds that flow from the north pole [11]. Cold trapped by craters, this vapour might sup-port the formation of perennial ice-domes, summer ice [11] and, possibly, of ice in those craters where our mounds occur (Fig. 3). Under past orbital solutions consistent with thaw processes [16], this crater-based ice could have thawed, forming paleolakes in situ; in turn, this might have triggered a series of periglacial events that led to the formation of closed pingos. Such conditions have been previously invoked to explain the enigmatic occurrence of gullies at these latitudes [17]. Alternative hypothesis #1: Central uplift com-plexes occur in Martian craters above 8 km in diame-ter [18]. Using MOLA data we have created crater profiles to evaluate whether the crater-based mounds are central peaks that have been covered in sedimen-tary material [12]. By calculating the fill level in the mound craters, we have found that this is approxi-mately equal to that of the surrounding plains [12]. This places the mounds well above the heights esti-mated for central peaks in these craters [18].  Alternative hypothesis #2: Impact-related hydro-thermal activity [19] could be the progenitor of the crater-floor mounds. For example, amongst the geo-logical traits observed at the Hesperian-aged Toro im-pact crater (17.00 E; 289.20 N) are mounds, polygonal fractures, veins and structural discontinuities that could be the result of volatile release and/or liquid flows [20-21]. Distinctive mineralogy and abundances of hy-drated phases in and around the central uplift complex, perhaps associated with impact-melt bearing crater-fill deposits, also are consistent with a hydrothermal origin [20]. By contrast, the crater-fill in the UP mound cra-ters post-dates the impact-formation of these craters and, thus, cannot be a product of impact-related hydro-thermal processes. Moreover, were the mounds geo-logical artefacts of impact-related processes, they would occur at or near the “true” crater floor and not at their current elevation datum.  Discussion: In terms of morphology, size, density of distribution and spatial association with small-sized polygons, the crater-floor mounds of northern UP ap-proximate closed pingos such as those observed in the TC. Recent hypotheses linking a) crater-floor polygons to desiccated paleolakes; b) water-vapour laden winds to the accumulation of crater-based ice; and, c) thaw conditions rooted in past orbital solutions, bolster the viability of this interpretation. References: [1] Mackay, J.R. (1998). GPQ 52, 3, 1-53. [2] French, H.M. (2007). The Periglacial Env., Wiley, England. [3] Soare, R.J. et al. (2005). Icarus 174, 173-182. [4] Soare, R.J. et al. (2005). LPS XXXVI, Abstract # 1102. [5] Dundas, C.M. et al. (2008). GRL doi:10. 1029/2007GL031798. [6] de Pablo, M.A. & Komatsu, G. (2009). Icarus 199, 9, 49-74. [7] Burr, D.M. et al. (2009). PSS 57, 56, 579-596. [8] Burr, D.M. et al. (2009). PSS 57, 56, 541-555. [9] Dundas, C.M. et al. (2010). Icarus 205, 1, 244-258. [10] Conway, S. et al. (2011). LPS XXXXII, Abstract # 2030. [11] El Maarry, M.R. et al. (2010). JGR 115, E10006doi:10.1029/2010JE00 3609. [12] Soare, R.J. et al. (2011). LPS XXXXII, Abstract # 1364. [13] Lachen-bruch, A.H. (1962). GSA Special Paper 70. [14] Feldman, W.C. et al. (2004). JGR 109, doi:10.10292003JE002160. [15] Boynton, W.V. et al. (2004). SSR 110, 37-83. [16] Costard, F. et al. (2002). Science 295, 5522, 110-113. [17] Gallagher, C. et al. (2010) Icarus 211, 458-471. [18] Garvin et al. (2000). 6th Mars Conf. Abstract # 3277. [19] Newsom, H.E. (1980). Icarus 44, 207-216. [20] Marzo, G.A. et al. (2010). Icarus 208, 667-683 [21] Fairén, A.G. et al. (2010). PNAS 107, 12,095-12,100, doi:10.1073/pnas.1002 889107. 6005.pdfFifth Mars Polar Science Conference (2011)

Possible crater-based pingos, paleolakes and periglacial landscapes in the high latitudes of Utopia Planitia, Mars

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