The Large Dendritic Morphologies in the Antoniadi Crater (Mars) and Their Potential Astrobiological Significance

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.

Perseverance rover reveals an ancient delta-lake system and flood deposits at Jezero crater, Mars

[Figure: see text].

Estimated Minimum Life Span of the Jezero Fluvial Delta (Mars)

The paleo-lake floor at the edge of the Jezero delta has been selected as the NASA 2020 rover landing site. In this article, we demonstrate the sequences of lake filling and delta formation and constrain the minimum life span of the Jezero paleo-lake from sedimentological and hydrological analyses. Two main phases of delta evolution can be recognized by utilizing imagery provided by the High Resolution Imaging Science Experiment (NASA Mars Reconnaissance Orbiter) and High Resolution Stereo Camera (ESA Mars Express): (1) basin infilling before the breaching of the Jezero rim and (2) the delta formation itself. Our results suggest that delta formation occurred over a minimum period of 90-550 years of hydrological activity. Breaching of the Jezero rim occurred in at least three distinct episodes, which spanned a far longer time-period than overall delta formation. This evolutionary history implies that the Jezero-lake floor would have been a haven for fine-grained sediment accumulation and hosted an active environment of significant astrobiological importance.

Bacterial Diversity of a High-Altitude Permafrost Thaw Pond Located on Ojos del Salado (Dry Andes, Altiplano-Atacama Region)

Microbial ecology of permafrost, due to its ecological and astrobiological importance, has been in the focus of studies in past decades. Although permafrost is an ancient and stable environment, it is also subjected to current climate changes. Permafrost degradation often results in generation of thaw ponds, a phenomenon not only reported mainly from polar regions but also present in high-altitude permafrost environments. Our knowledge about microbial communities of thaw ponds in these unique, remote mountain habitats is sparse. This study presents the first culture collection and results of the next-generation DNA sequencing (NGS) analysis of bacterial communities inhabiting a high-altitude permafrost thaw pond. In February 2016, a permafrost thaw pond on the Ojos del Salado at 5900 m a.s.l. (meters above sea level) was sampled as part of the Hungarian Dry Andes Research Programme. A culture collection of 125 isolates was established, containing altogether 11 genera belonging to phyla Bacteroidetes, Actinobacteria, and Proteobacteria. Simplified bacterial communities with a high proportion of candidate and hitherto uncultured bacteria were revealed by Illumina MiSeq NGS. Water of the thaw pond was dominated by Bacteroidetes and Proteobacteria, while in the sediment of the lake and permafrost, members of Acidobacteria, Actinobacteria, Bacteroidetes, Patescibacteria, Proteobacteria, and Verrucomicrobia were abundant. This permafrost habitat can be interesting as a potential Mars analog.

Geological Evidence of Planet-Wide Groundwater System on Mars

The scale of groundwater upwelling on Mars, as well as its relation to sedimentary systems, remains an ongoing debate. Several deep craters (basins) in the northern equatorial regions show compelling signs that large amounts of water once existed on Mars at a planet-wide scale. The presence of water-formed features, including fluvial Gilbert and sapping deltas fed by sapping valleys, constitute strong evidence of groundwater upwelling resulting in long term standing bodies of water inside the basins. Terrestrial field evidence shows that sapping valleys can occur in basalt bedrock and not only in unconsolidated sediments. A hypothesis that considers the elevation differences between the observed morphologies and the assumed basal groundwater level is presented and described as the "dike-confined water" model, already present on Earth and introduced for the first time in the Martian geological literature. Only the deepest basins considered in this study, those with bases deeper than -4000 m in elevation below the Mars datum, intercepted the water-saturated zone and exhibit evidence of groundwater fluctuations. The discovery of these groundwater discharge sites on a planet-wide scale strongly suggests a link between the putative Martian ocean and various configurations of sedimentary deposits that were formed as a result of groundwater fluctuations during the Hesperian period. This newly recognized evidence of water-formed features significantly increases the chance that biosignatures could be buried in the sediment. These deep basins (groundwater-fed lakes) will be of interest to future exploration missions as they might provide evidence of geological conditions suitable for life.

Paleolakes of Northeast Hellas: Precipitation, Groundwater-Fed, and Fluvial Lakes in the Navua-Hadriacus-Ausonia Region, Mars

The slopes of northeastern Hellas Basin, Mars exhibit a wide variety of fluvial landforms. In addition to the Dao-Niger-Harmakhis-Reull Valles outflow channels, many smaller channels and valleys cut into this terrain, several of which include discontinuous sections. We have mapped these channels and channel-associated depressions to investigate potential paleolakes from the Navua Valles in the West, through the Hadriacus Mons volcano in the center, to the Ausonia Montes in the East. We have identified three groups of candidate paleolakes at the source regions of major drainages and a fourth paleolake type scattered along the lower reaches of these drainages. Each paleolake group has a distinct character, determined by different formative processes, including precipitation and groundwater for lakes at the channel sources, and fluvially transported water at the lower channel reaches. Only one of these 34 basins had been cataloged previously in paleolake basin databases. Several of these sites are at proximity to the Hadriacus volcanic center, where active dikes during the Hesperian could have produced hydrothermal systems and habitable environments. Deposits within these paleolake depressions and at the termini of channels connected to these candidate paleolakes contain the geological and potentially biological record of these environments.

Fluvial geomorphology on Earth-like planetary surfaces: A review

Morphological evidence for ancient channelized flows (fluvial and fluvial-like landforms) exists on the surfaces of all of the inner planets and on some of the satellites of the Solar System. In some cases, the relevant fluid flows are related to a planetary evolution that involves the global cycling of a volatile component (water for Earth and Mars; methane for Saturn's moon Titan). In other cases, as on Mercury, Venus, Earth's moon, and Jupiter's moon Io, the flows were of highly fluid lava. The discovery, in 1972, of what are now known to be fluvial channels and valleys on Mars sparked a major controversy over the role of water in shaping the surface of that planet. The recognition of the fluvial character of these features has opened unresolved fundamental questions about the geological history of water on Mars, including the presence of an ancient ocean and the operation of a hydrological cycle during the earliest phases of planetary history. Other fundamental questions posed by fluvial and fluvial-like features on planetary bodies include the possible erosive action of large-scale outpourings of very fluid lavas, such as those that may have produced the remarkable canali forms on Venus; the ability of exotic fluids, such as methane, to create fluvial-like landforms, as observed on Saturn's moon, Titan; and the nature of sedimentation and erosion under different conditions of planetary surface gravity. Planetary fluvial geomorphology also illustrates fundamental epistemological and methodological issues, including the role of analogy in geomorphological/geological inquiry.

Evidence for Persistent Flow and Aqueous Sedimentation on Early Mars

Landforms representative of sedimentary processes and environments that occurred early in martian history have been recognized in Mars Global Surveyor Mars Orbiter Camera and Mars Odyssey Thermal Emission Imaging System images. Evidence of distributary, channelized flow (in particular, flow that lasted long enough to foster meandering) and the resulting deposition of a fan-shaped apron of debris indicate persistent flow conditions and formation of at least some large intracrater layered sedimentary sequences within fluvial, and potentially lacustrine, environments.

Water and the martian landscape

Over the past 30 years, the water-generated landforms and landscapes of Mars have been revealed in increasing detail by a succession of spacecraft missions. Recent data from the Mars Global Surveyor mission confirm the view that brief episodes of water-related activity, including glaciation, punctuated the geological history of Mars. The most recent of these episodes seems to have occurred within the past 10 million years. These new results are anomalous in regard to the prevailing view that the martian surface has been continuously extremely cold and dry, much as it is today, for the past 3.9 billion years. Interpretations of the new data are controversial, but explaining the anomalies in a consistent manner leads to potentially fruitful hypotheses for understanding the evolution of Mars in relation to Earth.