Microbial Response to Increased Temperatures Within a Lava-Induced Hydrothermal System in Iceland: An Analogue for the Habitability of Volcanic Terrains on Mars

Fossil hydrothermal systems on Mars are important exploration targets because they may have once been habitable and could still preserve evidence of microbial life. We investigated microbial communities within an active lava-induced hydrothermal system associated with the 2014-2015 eruption of Holuhraun in Iceland as a Mars analogue. In 2016, the microbial composition in the lava-heated water differed substantially from that of the glacial river and spring water sources that fed into the system. Several taxonomic and metabolic groups were confined to the water emerging from the lava and some showed the highest sequence similarities to subsurface ecosystems, including to the predicted thermophilic and deeply branching Candidatus Acetothermum autotrophicum. Measurements show that the communities were affected by temperature and other environmental factors. In particular, comparing glacial river water incubated in situ (5.7°C, control) with glacial water incubated within a lava-heated stream (17.5°C, warm) showed that microbial abundance, richness, and diversity increased in the warm treatment compared with the control, with the predicted major metabolism shifting from lithotrophy toward organotrophy and possibly phototrophy. In addition, thermophilic bacteria isolated from the lava-heated water and a nearby acidic hydrothermal system included the known endospore-formers Geobacillus stearothermophilus and Paenibacillus cisolokensis as well as a potentially novel taxon within the order Hyphomicrobiales. Similar lava-water interactions on Mars could therefore have generated habitable environments for microbial communities.

Automated detection of geological landforms on Mars using Convolutional Neural Networks

The large volume of high-resolution images acquired by the Mars Reconnaissance Orbiter has opened a new frontier for developing automated approaches to detecting landforms on the surface of Mars. However, most landform classifiers focus on crater detection, which represents only one of many geological landforms of scientific interest. In this work, we use Convolutional Neural Networks (ConvNets) to detect both volcanic rootless cones and transverse aeolian ridges. Our system, named MarsNet, consists of five networks, each of which is trained to detect landforms of different sizes. We compare our detection algorithm with a widely used method for image recognition, Support Vector Machines (SVMs) using Histogram of Oriented Gradients (HOG) features. We show that ConvNets can detect a wide range of landforms and has better accuracy and recall in testing data than traditional classifiers based on SVMs.

Rootless tephra stratigraphy and emplacement processes

Volcanic rootless cones are the products of thermohydraulic explosions involving rapid heat transfer from active lava (fuel) to external sources of water (coolant). Rootless eruptions are attributed to molten fuel-coolant interactions (MFCIs), but previous studies have not performed systematic investigations of rootless tephrostratigraphy and grain-size distributions to establish a baseline for evaluating relationships between environmental factors, MFCI efficiency, fragmentation, and patterns of tephra dispersal. This study examines a 13.55-m-thick vertical section through an archetypal rootless tephra sequence, which includes a rhythmic succession of 28 bed pairs. Each bed pair is interpreted to be the result of a discrete explosion cycle, with fine-grained basal material emplaced dominantly as tephra fall during an energetic opening phase, followed by the deposition of coarser-grained material mainly as ballistic ejecta during a weaker coda phase. Nine additional layers are interleaved throughout the stratigraphy and are interpreted to be dilute pyroclastic density current (PDC) deposits. Overall, the stratigraphy divides into four units: unit 1 contains the largest number of sediment-rich PDC deposits, units 2 and 3 are dominated by a rhythmic succession of bed pairs, and unit 4 includes welded layers. This pattern is consistent with a general decrease in MFCI efficiency due to the depletion of locally available coolant (i.e., groundwater or wet sediments). Changing conduit/vent geometries, mixing conditions, coolant and melt temperatures, and/or coolant impurities may also have affected MFCI efficiency, but the rhythmic nature of the bed pairs implies a periodic explosion process, which can be explained by temporary increases in the water-to-lava mass ratio during cycles of groundwater recharge.

Rootless cones on Mars: a consequence of lava-ground ice interaction

Fields of small cratered cones on Mars are interpreted to have formed by rootless eruptions due to explosive interaction of lava with ground ice contained within the regolith beneath the flow. Melting and vaporization of the ice, and subsequent explosive expansion of the vapour, act to excavate the lava and construct a rootless cone around the explosion site. Similar features are found in Iceland, where flowing lavas encountered water-saturated substrates. The martian cones have basal diameters of c. 30–1000 m and are located predominantly in the northern volcanic plains. High-resolution Mars Orbiter Camera images offer significant improvements over Viking data for interpretation of cone origins. A new model of the dynamics of cone formation indicates that very modest amounts of water ice are required to initiate and sustain the explosive interactions that produced the observed features. This is consistent with the likely low availability of water ice in the martian regolith. The scarcity of impact craters on many of the host lava flows indicates very young ages, suggesting that ground ice was present as recently as <10–100 Ma, and may persist today. Rootless cones therefore act as a spatial and temporal probe of the distribution of ground ice on Mars, which is of key significance in understanding the evolution of the martian climate. The location of water in liquid or solid form is of great importance to future robotic and human exploration strategies, and to the search for extraterrestrial life.