Abstract
Mars has held large amounts of running and standing water throughout its history, as evidenced by numerous morphologies attributed to rivers, outflow channels, lakes, and possibly an ocean. This work examines the crater Antoniadi located in the Syrtis Major quadrangle. Some parts of the central area of the crater exhibit giant polygonal mud cracks, typical of endured lake bottom, on top of which a dark, tens of kilometers-long network of dendritic (i.e., arborescent) morphologies emerges, at first resembling the remnant of river networks. The network, which is composed of tabular sub-units, is in relief overlying hardened mud, a puzzling feature that, in principle, could be explained as landscape inversion resulting from stronger erosion of the lake bottom compared to the endured crust of the riverine sediments. However, the polygonal mud cracks have pristine boundaries, which indicate limited erosion. Furthermore, the orientation of part of the network is the opposite of what the flow of water would entail. Further analyses indicate the similarity of the dendrites with controlled diffusion processes rather than with the river network, and the presence of morphologies incompatible with river, alluvial, or underground sapping processes, such as overlapping of branches belonging to different dendrites or growth along fault lines. An alternative explanation worth exploring due to its potential astrobiological importance is that the network is the product of ancient reef-building microbialites on the shallow Antoniadi lake, which enjoyed the fortunate presence of a heat source supplied by the Syrtis Major volcano. The comparison with the terrestrial examples and the dating of the bottom of the crater (formed at 3.8 Ga and subjected to a resurfacing event at 3.6 Ga attributed to the lacustrine drape) contribute to reinforcing (but cannot definitely prove) the scenario of microbialitic origin for dendrites. Thus, the present analysis based on the images available from the orbiters cannot be considered proof of the presence of microbialites in ancient Mars. It is concluded that the Antoniadi crater could be an interesting target for the research of past Martian life in future landing missions.
Highlights
Mars has held large amounts of running and standing water throughout its history, as evidenced by numerous morphologies attributed to rivers, outflow channels, lakes, and possibly an ocean
Antoniadi is a 400 km wide impact crater located in the Syrtis Major quadrangle at the coordinates 21◦ N and 230◦ W (Figure 1)
Possible lava flows from Syrtis Major mixed with indeterminate units emerge in the southern part, while two large areas, one to the north and one to the south, appear in the CTX, Thermal Emission Imaging System (THEMIS), and HiRISE images as altered by diverse geological and geomorphological factors such as faults and periglacial processes
Summary
The quest for possible ancient forms of life in the Universe and, in particular, for Martian life is largely a search for areas of former water abundance, e.g., [1,2,3,4]. Morphological indications for water include outflow channels between the southern highlands and the north plains, and valley networks carved on ancient and cratered areas of the planet [5,6,7,8,9,10]. Except for a study of the mineralogy of the area southeast of Antoniadi, where the presence of diagenetic quartz was established [31,32], there are no works entirely dedicated to this crater and its dendritic morphologies
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