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Microbial fossils preserved by early diagenetic chert provide a window into the Proterozoic biosphere, but seawater chemistry, microbial processes, and the interactions between microbes and the environment that contributed to this preservation are not well constrained. Here, we use fossilization experiments to explore the processes that preserve marine cyanobacterial biofilms by the precipitation of amorphous silica in a seawater medium that is analogous to Proterozoic seawater. These experiments demonstrate that the exceptional silicification of benthic marine cyanobacteria analogous to the oldest diagnostic cyanobacterial fossils requires interactions among extracellular polymeric substances (EPS), photosynthetically induced pH changes, magnesium cations (Mg2+ ), and >70 ppm silica.

Silicification was a major mode of fossilization in Proterozoic peritidal environments, but marine silica concentrations and the chemical and biological mechanisms that drove microbial silicification and formation of early diagenetic chert in these environments remain poorly constrained. Here, we use taphonomy experiments to demonstrate that photosynthetically active cyanobacteria that are morphologically analogous to the oldest cyanobacterial fossil, Eoentophysalis, mediate the formation of magnesium-rich amorphous silica in seawater that is undersaturated with respect to silica. These results show that microbes in Proterozoic tidal environments may have mediated their own silicification at lower silica concentrations than previously assumed.

Theory and observation for the search for life on exoplanets via atmospheric "biosignature gases" is accelerating, motivated by the capabilities of the next generation of space- and ground-based telescopes. The most observationally accessible rocky planet atmospheres are those dominated by molecular hydrogen gas, because the low density of H$_2$-gas leads to an expansive atmosphere. The capability of life to withstand such exotic environments, however, has not been tested in this context. We demonstrate that single-celled microorganisms ($\textit{E. coli}$ and yeast) that normally do not inhabit H$_2$-dominated environments can survive and grow in a 100% H$_2$ atmosphere. We also describe the astonishing diversity of dozens of different gases produced by $\textit{E. coli}$, including many already proposed as potential biosignature gases (e.g., nitrous oxide, ammonia, methanethiol, dimethylsulfide, carbonyl sulfide, and isoprene). This work demonstrates the utility of lab experiments to better identify which kinds of alien environments can host some form of possibly detectable life., Nature Astronomy https://doi.org/10.1038/s41550-020-1069-4. V2 has a typo correction

Hot super Earths are exoplanets with short orbital periods ($$ 0.4) in the Kepler band (420-900 nm). We are motivated to determine whether reflection from molten lava and quenched glasses (a product of rapidly cooled lava) on the surfaces of hot super Earths contributes to the observationally inferred high geometric albedos. We experimentally measure reflection from rough and smooth textured quenched glasses of both basalt and feldspar melts. For lava reflectance values, we use specular reflectance values of molten silicates from non-crystalline solids literature. Integrating the empirical glass reflectance function and non-crystalline solids reflectance values over the dayside surface of the exoplanet at secondary eclipse yields an upper limit for the albedo of a lava-quenched glass planet surface of $\sim $0.1. We conclude that lava planets with solid (quenched glass) or liquid (lava) surfaces have low albedos. The high albedos of some hot super Earths are most likely explained by atmospheres with reflective clouds (or, for a narrow range of parameter space, possibly Ca/Al oxide melt surfaces). Lava planet candidates in TESS data can be identified for follow-up observations and future characterization., Comment: 18 pages, 14 figures, 4 tables, published in ApJ

Nanospacecraft could enable detailed characterization of many asteroids in a small timeframe by launching multiple spacecraft simultaneously to visit a large set of targets. To be able to characterize as large of a set of asteroids as possible, however, visits to individual asteroids would be limited to flybys, which would have to be autonomous. As an additional challenge, due to the limitations of nanospacecraft and a massively parallel architecture, Earth-based localization and communication infrastructure, such as the Deep Space Network, cannot be relied upon. We have developed an optical instrument prototype and an image simulation system for autonomous asteroid flybys and 3D multispectral mapping using nanospacecraft. The final system is targeted to fit into a single CubeSat unit (a 10 cm cube) and to have the mass of less than 1 kg. The images are used for structure from motion algorithms to determine the quality of 3D reconstruction to be expected from this mission. We are presenting the instrument design, the simulation system, and the simultaneous localization and mapping system developed for nanospacecraft asteroid flybys.

Siliciclastic sediments of the Ediacaran Period contain exceptionally preserved fossils of macroscopic organisms, including three-dimensional casts and molds commonly found in sandstones and siltstones and some two-dimensional compressions reported in shales. The sporadic and variable associations of these exceptionally preserved macroscopic fossils with pyrite, clay minerals, and microbial fossils and textures complicate our understanding of fossilization processes. This hinders inferences about the evolutionary histories, tissue types, original morphologies, and lifestyles of the enigmatic Ediacara biota. Here, we investigate the delayed decay of scallop muscles buried in quartz sand or kaolinite for 45 days. This process occurs in the presence of microbial activity in mixed redox environments, but in the absence of thick, sealing microbial mats. Microbial processes that mediate organic decay and release the highest concentrations of silica and Fe(II) into the pore fluids are associated with the most extensive tissue decay. Delayed decay and the preservation of thick muscles in sand are associated with less intense microbial iron reduction and the precipitation of iron oxides and iron sulfides that contain Fe(II) or Fe(III). In contrast, muscles buried in kaolinite are coated only by, NASA Astrobiology Institute (Grant NNA13AA90A), Simons Foundation (Grants 327126 and 344707), American Chemical Society (Award 54498-ND8)

Oxygenic photosynthesis supplies organic carbon to the modern biosphere, but it is uncertain when this metabolism originated. It has previously been proposed1,2 that photosynthetic reaction centres capable of splitting water arose by about 3billion years ago on the basis of the inferred presence of manganese oxides in Archaean sedimentary rocks. However, this assumes that manganese oxides can be produced only in the presence of molecular oxygen3, reactive oxygen species4,5 or by high-potential photosynthetic reaction centres6,7. Here we show that communities of anoxygenic photosynthetic microorganisms biomineralize manganese oxides in the absence of molecular oxygen and high-potential photosynthetic reaction centres. Microbial oxidation of Mn(II) under strictly anaerobic conditions during the Archaean eon would have produced geochemical signals identical to those used to date the evolution of oxygenic photosynthesis before the Great Oxidation Event1,2. This light-dependent process may also produce manganese oxides in the photic zones of modern anoxic water bodies and sediments.

We propose a distributed close-range survey of hundreds of asteroids representing many asteroid families, spectral types and sizes. This can be implemented by a fleet of nanospacecraft (e.g., 4–5-unit CubeSats) equipped with miniature imaging and spectral instruments (from near ultraviolet to near infrared). To enable the necessary large delta-v, each spacecraft carries a single electric sail tether which taps the momentum from the solar wind. Data are stored in a flash memory during the mission and downlinked at an Earth flyby. This keeps deep-space network telemetry costs down, despite the large number of individual spacecraft. To navigate without the use of the deep-space network, optical navigation is required to track stars, planets and asteroids. The proposed mission architecture is scalable both scientifically and financially. A fleet of 50 spacecraft will be able to obtain images and spectral data from 200 to 300 near-Earth and main belt asteroids. It allows study of those asteroid families and spectroscopic types for which currently no close-range observations are available. This paper presents science objectives, overall science traceability matrix, example targets and technical challenges associated with the mission. We open to discuss preliminary requirements, mission and spacecraft designs.