Search

Primary support for ancient Martian oceans has relied on qualitative interpretations of hypothesized shorelines on relatively low‐resolution images and data. We present a toolkit for quantitatively identifying paleoshorelines using topographic, morphological, and spectroscopic evaluations. In particular, we apply the validated topographic expression analysis of Hare et al. (2001, https://doi.org/10.1029/2001JB000344) for the first time beyond Earth, focusing on a test case of putative shoreline features along the Arabia level in northeast Cydonia Mensae, as first described by Clifford and Parker (2001, https://doi.org/10.1006/icar.2001.6671). Our results show these curvilinear features are inconsistent with a wave‐generated shoreline interpretation. The topographic expression analysis identifies a few potential shoreline terraces along the historically proposed contacts, but these tilt in different directions, do not follow an equipotential surface (even accounting for regional tilting), and are not laterally continuous. Lineaments appear blocky in nature at small scales, and they bifurcate, truncate, and merge along track. These features are more consistent with material boundaries for lithological units exposed along a degraded crater wall. These results do not preclude the existence of an ancient hemispheric ocean, but the geophysical and high‐resolution topographic data at this site do not support such an interpretation. Plain Language Summary: There is an ongoing controversy about whether Mars had ancient oceans. Abundant evidence for past surface liquid water exists, but it is debated how much and for how long it persisted on Mars' surface. Features have previously been traced out in relatively low‐resolution images and interpreted as shorelines of episodic ancient oceans. However, new high‐resolution data allow for better and more complete analyses. Here we present methods to determine whether any proposed ancient shoreline feature meets the requirements to be classified as a shoreline using these improved data. Shorelines should form flat "step‐like" landforms at a near‐constant elevation, so one critical analysis looks at the shape and elevation of proposed features. We examine a site that has been promoted in the literature as an exemplar of ancient shorelines and find that this site lacks a diagnostic shoreline shape. Instead, features at this site are better explained as exposed and eroded rock layers that mimic shoreline shapes in low‐resolution images. Our findings do not mean that oceans never existed on Mars, only that this specific site does not support the ocean hypothesis. Application of our methods to similar sites could shed further light on the ocean hypothesis. Key Points: We apply a proposed paleoshoreline‐identification toolkit to newer high‐resolution data of an exemplar site for paleoshorelines on MarsAny wave‐generated paleoshorelines should exhibit expressions identifiable in the residual topography from an idealized slopeOur analysis of these curvilinear features does not support a paleoshoreline interpretation and is more consistent with eroded lithologies [ABSTRACT FROM AUTHOR]

Abstract: Many putative water-related features exist in the northern lowlands of Mars. These features may provide clues to the abundance and timing of water or ice that existed there in the past. The Cydonia Mensae and Southern Acidalia area was chosen as the study area owing to the abundance of two of these features: giant polygons and pitted cones. In addition a section of the Deuteronilus shoreline is located there. The abundance and close proximity of the features makes this area an excellent place to study the spatial relationships between these landforms, as well as the morphological characteristics of pitted cones. The features were mapped into a GIS for spatial analyses. The highest densities of pitted cones and giant polygons are adjacent but distinctly separated by a knobby ridge that is surrounded by the Deuteronilus putative shoreline. Pitted cones were measured and examined to determine if a classification by morphology is possible, but the results were inconclusive. Statistical tests on pit-to-cone diameter ratios and tests of surface temperatures of cone material suggest, but do not verify, a single cone origin. The various shapes, sizes, and putative ages of pitted cones may be attributed to temporal variation in emplacement and spatial variation in material properties. Among the possible scenarios put forth for pitted cone genesis on Mars two are likely candidates in Cydonia Mensae: (1) the sublimation of a cold-based glacier, and (2) a buried lens of methane and/or CO2 clathrates. [Copyright &y& Elsevier]

AbstractRecent findings on the presence of water on Mars (Baker, V.R. (2006). Geomorphological evidence for water on Mars. Elements2(3), 139?143; DeJong, E. (2006). Geological evidence of the presence of water on Mars. Abstracts from the 40th Western Regional Meeting of the American Chemical Society, Anaheim, CA, January, 2006, pp. 22?25. American Chemical Society, Washington, DC; McSween, H.Y. Jr. (2006). Water on Mars. Elements2(3), 135?137; Mitrofanov, I.G. (2005). Water explorations on Mars. Priroda9, 34?43) strongly suggest that there existed a period of chemical evolution eventually leading to life processes on primitive Mars (Kanavarioti, A. & Maneinelli, R.L. (1990). Could organic matter have been preserved on Mars for 3.5 billion years. Icarus84, 196?202). Owing to the adverse conditions, it is quite likely that the process of chemical evolution would have been suppressed and any living organisms that formed would have become extinct over time on Mars. The presence of water as a necessity for the survival of living organisms and the presence of grey haematite, originated under aqueous conditions, have led us to investigate the possible role of haematite in the chemical evolution on Mars. Our observations suggest that iron oxide hydroxide (FeOOH), a precursor of haematite, has a much higher binding affinity towards ribose nucleotides (the building blocks of RNA) than the haematite itself. This would mean that during the process of haematite formation, especially through the probable process of Fe3+hydrolysis by aqueous ammonia, the precursors of haematite might have played a significant role in the processes leading to chemical evolution and the possible origin of life on Mars. [ABSTRACT FROM AUTHOR]