Future Exoplanet Research: Science Questions and How to Address Them

Started approximately in the late 1980s, exoplanetology has up to now unveiled the main gross bulk characteristics of planets and planetary systems. In the future it will benefit from more and more large telescopes and advanced space missions. These instruments will dramatically improve their performance in terms of photometric precision, detection speed, multipixel imaging, high-resolution spectroscopy, allowing to go much deeper in the knowledge of planets. Here we outline some science questions which should go beyond these standard improvements and how to address them. Our prejudice is that one is never too speculative: experience shows that the speculative predictions initially not accepted by the community have been confirmed several years later (like spectrophotometry of transits or circumbinary planets).Comment: Invited review, accepte

Hamelin Pool Microbialites: Images of vertical sections and thin section scans

Forty-five microbialite heads were collected from Hamelin Pool between 2012 and 2014. Repository contains images of polished slabs, slabs showing the location of thin sections, and thin section scans from each sample. Sample location map and inventory list are also included.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Authigenic clays as precursors to carbonate precipitation in saline lakes of Salar de Llamara, Northern Chile

In this study, we examined associations between microbial communities, Mg-clay minerals, and carbonates in microbial mat samples from the Puquios of the Salar de Llamara using scanning electron microscopy, energy dispersive X-ray spectroscopy, focused ion beam nanotomography, and transmission electron microscopy. Data shared here correspond to Figs. 4-6, and include the raw data used to create the Supplemental Videos 1 and 2.THIS DATASET IS ARCHIVED AT DANS/EASY, BUT NOT ACCESSIBLE HERE. TO VIEW A LIST OF FILES AND ACCESS THE FILES IN THIS DATASET CLICK ON THE DOI-LINK ABOV

Stromatolite provinces of Hamelin Pool: physiographic controls on stromatolites and associated lithofacies

Recent studies recognized distinct stromatolite provinces in Hamelin Pool, Western Australia, each with morphologically distinct stromatolite structures paired with characteristic shelf physiography. In the present paper, we couple detailed lithofacies mapping with Hamelin Pool bathymetry and consider physiography as a control of sedimentation processes, including stromatolite development. Bathymetric transects, derived from a high-resolution bathymetry map with depths from 0 to 11 meters, allow calculation of slope gradients in the provinces. As in other settings, bathymetry is linked to energy regimes, which in turn appear to be coupled with variations in stromatolite morphologies and associated lithofacies as follows: (1) low-gradient ramps with low-energy settings are associated with sheet mats and elongate-clustered stromatolites that exhibit regular spatial patterns, possibly indicative of self-organization; (2) low gradients coupled with high-energy settings resulting from strong winds result in seif stromatolites with pronounced directional bands; (3) medium to steep gradients coupled with medium to high energy are associated with individual and merged stromatolites, often with thin basal necks; (4) headlands and promontories where the topography deflects currents are associated with elongate-nested stromatolites; and (5) medium- to high-energy slopes typically found at promontory edges and shelf margins are dominated by blocky pavement. Observations linking stromatolite morphology to physiography in a modern microbial system provide insight into the long-lived debate about biology versus environment in controlling stromatolite morphology. When physiography leads to a high-energy regime, environmental controls are the main factor determining stromatolite morphology. In contrast, when physiography promotes a low-energy environment, the response of biological communities becomes the main driver of macroscale stromatolite morphology

Initial Accretion in Hamelin Pool Microbialites: The Role of Entophysalis in Precipitation of Microbial Micrite

One of the largest assemblages of living marine microbialites, with shapes and sizes analogous to ancient structures, is found along the margins of Hamelin Pool, Shark Bay, Western Australia. An investigation of microbial mats on the surfaces of these structures using petrographic analysis, light, and scanning electron microscopy identified the in situ precipitation of micrite as an important accretion mechanism in all major mat types (pustular, smooth, and colloform). Within each mat type, peloidal micrite, composed of nano-bulbous spheres to tabular and rod-shaped crystals, was closely linked with cells of the coccoid cyanobacterium Entophysalis, and microtextures of the micrite reflected the size and distribution of Entophysalis colonies. In pustular surface mats, where large colonies of Entophysalis were common, large clots of micrite were distributed randomly throughout the mat. In contrast, in smooth and colloform mats, where smaller colonies of Entophysalis were distributed along horizons, micrite formed fine laminae. In all surface mat types, micrite associated with Entophysalis had a characteristic honeycomb appearance, resulting from cell and/or colony entombment. These findings redefine our understanding of microbialite accretion in Hamelin Pool, recognizing the importance of microbial micrite in microbialite growth and showing that coccoid cyanobacteria are capable of building laminated structures. Moreover, Entophysalis, the dominant visible microbe associated with the precipitation of micrite in Hamelin Pool, has a lineage to Eoentophysalis, found throughout early and middle Proterozoic microbialites assemblages. These findings reinforce the importance of Hamelin Pool as a window to the past

The microbial carbonate factory of Hamelin Pool, Shark Bay, Western Australia

Microbialites and peloids are commonly associated throughout the geologic record. Proterozoic carbonate megafacies are composed predominantly of micritic and peloidal limestones often interbedded with stromatolitic textures. The association is also common throughout carbonate ramps and platforms during the Phanerozoic. Recent investigations reveal that Hamelin Pool, located in Shark Bay, Western Australia, is a microbial carbonate factory that provides a modern analog for the microbialite-micritic sediment facies associations that are so prevalent in the geologic record. Hamelin Pool contains the largest known living marine stromatolite system in the world. Although best known for the constructive microbial processes that lead to formation of these stromatolites, our comprehensive mapping has revealed that erosion and degradation of weakly lithified microbial mats in Hamelin Pool leads to the extensive production and accumulation of sand-sized micritic grains. Over 40 km2 of upper intertidal shoreline in the pool contain unlithified to weakly lithified microbial pustular sheet mats, which erode to release irregular peloidal grains. In addition, over 20 km2 of gelatinous microbial mats, with thin brittle layers of micrite, colonize subtidal pavements. When these gelatinous mats erode, the micritic layers break down to form platey, micritic intraclasts with irregular boundaries. Together, the irregular micritic grains from pustular sheet mats and gelatinous pavement mats make up nearly 26% of the total sediment in the pool, plausibly producing ~ 24,000 metric tons of microbial sediment per year. As such, Hamelin Pool can be seen as a microbial carbonate factory, with construction by lithifying microbial mats forming microbialites, and erosion and degradation of weakly lithified microbial mats resulting in extensive production of sand-sized micritic sediments. Insight from these modern examples may have direct applicability for recognition of sedimentary deposits of microbial origin in the geologic record

Electrical conductivity as a driver of biological and geological spatial heterogeneity in the Puquios, Salar de Llamara, Atacama Desert, Chile

Abstract Reputed to be the driest desert in the world, the Atacama Desert in the Central Andes of Northern Chile is an extreme environment with high UV radiation, wide temperature variation, and minimum precipitation. Scarce lagoons associated with salt flats (salars) in this desert are the surface expression of shallow groundwater; these ponds serve as refugia for life and often host microbial communities associated with evaporitic mineral deposition. Results based on multidisciplinary field campaigns and associated laboratory examination of samples collected from the Puquios of the Salar de Llamara in the Atacama Desert during austral summer provide unprecedented detail regarding the spatial heterogeneity of physical, chemical, and biological characteristics of these salar environments. Four main lagoons (‘Puquios’) and more than 400 smaller ponds occur within an area less than 5 km2, and are characterized by high variability in electrical conductivity, benthic and planktonic biota, microbiota, lagoon bottom type, and style of mineral deposition. Results suggest that electrical conductivity is a driving force of system heterogeneity. Such spatial heterogeneity within the Puquios is likely to be expanded with temporal observations incorporating expected seasonal changes in electrical conductivity. The complexity of these Andean ecosystems may be key to their ability to persist in extreme environments at the edge of habitability

Environmental Pressures Influencing Living Stromatolites In Hamelin Pool, Shark Bay, Western Australia

Environmental parameters in Hamelin Pool, Shark Bay were investigated to characterize extrinsic factors that may be affecting stromatolite morphogenesis. Hamelin Pool, which evolved into a restricted environment during the last few millennia, sustains the world's most extensive and diverse assemblage of modern marine stromatolites. These stromatolites occur in a shallow nearshore facies belt covering over 100 km of coast. Temperature, salinity, water level, and current data collected between 2012 and 2014 have revealed previously undocumented regional and seasonal trends. Regional trends include increasing salinity, greater temperature range, and decreasing energy moving southward from Faure Sill and to the Nilemah Embayment. Seasonal trends reveal paradoxically increased salinities in wet winter months and decreased salinity in dry summer months. When paired with annual tidal cycles, these trends suggest the influx of low salinity groundwater along the Hamelin Pool shelf. Speculation on how the documented environmental parameters may affect stromatolite growth suggests potential impact on morphology, internal fabric, and stromatolite-building microbial communities. These insights into environmental pressures within a living stromatolite system provide a framework for understanding extrinsic factors affecting microbial communities and stromatolite development throughout Earth history

New multi-scale perspectives on the stromatolites of Shark Bay, Western Australia

A recent field-intensive program in Shark Bay, Western Australia provides new multi-scale perspectives on the world\u27s most extensive modern stromatolite system. Mapping revealed a unique geographic distribution of morphologically distinct stromatolite structures, many of them previously undocumented. These distinctive structures combined with characteristic shelf physiography define eight \u27Stromatolite Provinces\u27. Morphological and molecular studies of microbial mat composition resulted in a revised growth model where coccoid cyanobacteria predominate in mat communities forming lithified discrete stromatolite buildups. This contradicts traditional views that stromatolites with the best lamination in Hamelin Pool are formed by filamentous cyanobacterial mats. Finally, analysis of internal fabrics of stromatolites revealed pervasive precipitation of microcrystalline carbonate (i.e. micrite) in microbial mats forming framework and cement that may be analogous to the micritic microstructures typical of Precambrian stromatolites. These discoveries represent fundamental advances in our knowledge of the Shark Bay microbial system, laying a foundation for detailed studies of stromatolite morphogenesis that will advance our understanding of benthic ecosystems on the early Earth