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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.

In photosynthesis, collective pigment excitations – excitons – facilitate chemical reactions for sustainable biological function. Here, the effect of hydrostatic pressure – an important thermodynamic stress factor – on optical spectral properties of excitons in the cyclic light-harvesting 2 pigment-protein complex from photosynthetic bacterium Rhodoblastus acidophilus was first studied. The high pressure-induced modifications of absorption, fluorescence and polarized fluorescence excitation spectra were theoretically analyzed in terms of the disordered molecular exciton model. We uniquely show that the observed shift of the spectra under pressure is largely governed by the pressure-induced rise of two factors: the exciton displacement energy and the exciton coupling energy, which increases the spread of the exciton state manifold. A significant increase of static energy disorder revealed by model calculations suggests that high-pressure compressing of the complex is actually accompanied by altered spatial orientations and conformations of the protein-embedded pigment molecules.

This paper presents two technology experiments – the plasma brake for deorbiting and the electric solar wind sail for interplanetary propulsion – on board the ESTCube-2 and FORESAIL-1 satellites. Since both technologies employ the Coulomb interaction between a charged tether and a plasma flow, they are commonly referred to as Coulomb drag propulsion. The plasma brake operates in the ionosphere, where a negatively charged tether deorbits a satellite. The electric sail operates in the solar wind, where a positively charged tether propels a spacecraft, while an electron emitter removes trapped electrons. Both satellites will be launched in low Earth orbit carrying nearly identical Coulomb drag propulsion experiments, with the main difference being that ESTCube-2 has an electron emitter and it can operate in the positive mode. While solar-wind sailing is not possible in low Earth orbit, ESTCube-2 will space-qualify the components necessary for future electric sail experiments in its authentic environment. The plasma brake can be used on a range of satellite mass classes and orbits. On nanosatellites, the plasma brake is an enabler of deorbiting – a 300-m-long tether fits within half a cubesat unit, and, when charged with - 1 kV, can deorbit a 4.5-kg satellite from between a 700- and 500-km altitude in approximately 9–13 months. This paper provides the design and detailed analysis of low-Earth-orbit experiments, as well as the overall mission design of ESTCube-2 and FORESAIL-1.