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Abstract: Space bioprocess engineering (SBE) is an emerging multi-disciplinary field to design, realize, and manage biologically-driven technologies specifically with the goal of supporting life on long term space missions. SBE considers synthetic biology and bioprocess engineering under the extreme constraints of the conditions of space. A coherent strategy for the long term development of this field is lacking. In this Perspective, we describe the need for an expanded mandate to explore biotechnological needs of the future missions. We then identify several key parameters—metrics, deployment, and training—which together form a pathway towards the successful development and implementation of SBE technologies of the future.

In the coming years and decades, advanced space- and ground-based observatories will allow an unprecedented opportunity to probe the atmospheres and surfaces of potentially habitable exoplanets for signatures of life. Life on Earth, through its gaseous products and reflectance and scattering properties, has left its fingerprint on the spectrum of our planet. Aided by the universality of the laws of physics and chemistry, we turn to Earth's biosphere, both in the present and through geologic time, for analog signatures that will aid in the search for life elsewhere. Considering the insights gained from modern and ancient Earth, and the broader array of hypothetical exoplanet possibilities, we have compiled a comprehensive overview of our current understanding of potential exoplanet biosignatures, including gaseous, surface, and temporal biosignatures. We additionally survey biogenic spectral features that are well known in the specialist literature but have not yet been robustly vetted in the context of exoplanet biosignatures. We briefly review advances in assessing biosignature plausibility, including novel methods for determining chemical disequilibrium from remotely obtainable data and assessment tools for determining the minimum biomass required to maintain short-lived biogenic gases as atmospheric signatures. We focus particularly on advances made since the seminal review by Des Marais et al. The purpose of this work is not to propose new biosignature strategies, a goal left to companion articles in this series, but to review the current literature, draw meaningful connections between seemingly disparate areas, and clear the way for a path forward. Key Words: Exoplanets-Biosignatures-Habitability markers-Photosynthesis-Planetary surfaces-Atmospheres-Spectroscopy-Cryptic biospheres-False positives. Astrobiology 18, 663-708.

For the first time in human history, we will soon be able to apply thescientific method to the question "Are We Alone?" The rapid advance ofexoplanet discovery, planetary systems science, and telescope technology willsoon allow scientists to search for life beyond our Solar System through directobservation of extrasolar planets. This endeavor will occur alongside searchesfor habitable environments and signs of life within our Solar System. While thesearches are thematically related and will inform each other, they will requireseparate observational techniques. The search for life on exoplanets holdspotential through the great diversity of worlds to be explored beyond our SolarSystem. However, there are also unique challenges related to the relativelylimited data this search will obtain on any individual world. This white paperreviews the scientific community's ability to use data from future telescopesto search for life on exoplanets. This material summarizes products from theExoplanet Biosignatures Workshop Without Walls (EBWWW). The EBWWW wasconstituted by a series of online and in person activities, with participationfrom the international exoplanet and astrobiology communities, to assess stateof the science and future research needs for the remote detection of life onplanets outside our Solar System.

In the coming years and decades, advanced space- and ground-basedobservatories will allow an unprecedented opportunity to probe the atmospheresand surfaces of potentially habitable exoplanets for signatures of life. Lifeon Earth, through its gaseous products and reflectance and scatteringproperties, has left its fingerprint on the spectrum of our planet. Aided bythe universality of the laws of physics and chemistry, we turn to Earth'sbiosphere, both in the present and through geologic time, for analog signaturesthat will aid in the search for life elsewhere. Considering the insights gainedfrom modern and ancient Earth, and the broader array of hypothetical exoplanetpossibilities, we have compiled a state-of-the-art overview of our currentunderstanding of potential exoplanet biosignatures including gaseous, surface,and temporal biosignatures. We additionally survey biogenic spectral featuresthat are well-known in the specialist literature but have not yet been robustlyvetted in the context of exoplanet biosignatures. We briefly review advances inassessing biosignature plausibility, including novel methods for determiningchemical disequilibrium from remotely obtainable data and assessment tools fordetermining the minimum biomass required for a given atmospheric signature. Wefocus particularly on advances made since the seminal review by Des Marais etal. (2002). The purpose of this work is not to propose new biosignaturesstrategies, a goal left to companion papers in this series, but to review thecurrent literature, draw meaningful connections between seemingly disparateareas, and clear the way for a path forward.

The given text discusses the work of Gavriil A. Tikhov and Nikolai Tikhov in the field of astrobiology, exploring the possibility of life on other planets. It highlights their contributions to the study of extraterrestrial life, including the use of spectroscopic observations and isotopic composition as indicators of life. The text also discusses the properties of life in the universe and the adaptability of organisms to different environmental conditions. It concludes by emphasizing the need for further research in astrobiology and the potential for uncovering the secrets of life on other planets. [Extracted from the article]

An enduring question in astrobiology is how we assess extraterrestrial environments as being suitable for life. We suggest that the most reliable assessments of the habitability of extraterrestrial environments are made with respect to the empirically determined limits to known life. We discuss qualitatively distinct categories of habitability: empirical habitability that is constrained by the observed limits to biological activity; habitability sensu stricto, which is defined with reference to the known or unknown limits to the activity of all known organisms; and habitability sensu lato (habitability in the broadest sense), which is circumscribed by the limit of all possible life in the universe, which is the most difficult (and perhaps impossible) to determine. We use the cloud deck of Venus, which is temperate but incompatible with known life, as an example to elaborate and hypothesize on these limits. [ABSTRACT FROM AUTHOR]

Previous work on possible surface reflectance biosignatures for Earth-likeplanets has typically focused on analogues to spectral features produced byphotosynthetic organisms on Earth, such as the vegetation red edge. Althoughoxygenic photosynthesis, facilitated by pigments evolved to capture photons, isthe dominant metabolism on our planet, pigmentation has evolved for multiplepurposes to adapt organisms to their environment. We present aninterdisciplinary study of the diversity and detectability of nonphotosyntheticpigments as biosignatures, which includes a description of environments thathost nonphotosynthetic biologically pigmented surfaces, and a lab-basedexperimental analysis of the spectral and broadband color diversity ofpigmented organisms on Earth. We test the utility of broadband color todistinguish between Earth-like planets with significant coverage ofnonphotosynthetic pigments and those with photosynthetic or nonbiologicalsurfaces, using both 1-D and 3-D spectral models. We demonstrate that, givensufficient surface coverage, nonphotosynthetic pigments could significantlyimpact the disk-averaged spectrum of a planet. However, we find that due to thepossible diversity of organisms and environments, and the confounding effectsof the atmosphere and clouds, determination of substantial coverage bybiologically produced pigments would be difficult with broadband colors aloneand would likely require spectrally resolved data.

The field of astrobiology is concerned with the origin, evolution, and distribution of life in the Universe. It contains within it civilization-level questions such as: What is the future of humanity on Earth and can we successfully explore and settle other planets? As such, it offers an educational framework for both teaching basic science and for engaging individuals in questions about how society can take on its biggest challenges and opportunities. Life Beyond is a collaboration between the UK Centre for Astrobiology and the Scottish Prison Service (SPS) to take astrobiology into the prison environment. Using a pilot program across four Scottish prisons, a 4-week astrobiology course focused on designing a station for Mars was developed. Learning outcomes ranged from improvements in literacy, numeracy, and science skills to enhancing civic responsibilities. The results of the initiative are products such as Mars station designs, essays, and art, providing participants with tangible outputs. We describe the pilot initiative, the 4-week Life Beyond course, and draw conclusions about the use of astrobiology as a vehicle for teaching science and advancing social reform in the prison environment.

Beneath Enceladus' ice crust lies an ocean which might host habitable conditions. Here, the scale and productivity of a notional Enceladean methanogenic biosphere are computed as a function of the core‐to‐ocean flux of hydrogen and the ratio between abiotic and biotic methane in Enceladus' space plume. Habitats with an ocean‐top pH range of 8–9 have up to 40%–60% probability of being energy‐limited. Those at pH > 9 are increasingly uninhabitable, and those <8.5 are increasingly likely to host exponential growth, possibly leading to compositional inconsistencies between the ocean and Cassini gas observations. In those cases, energy‐based habitability models cannot infer an inhabited Enceladus consistent with both Earth life and Cassini measurements without including additional microbial growth limiters such as nutrient limitation, toxicity, or spatial constraints. If methanogens are isolated to a 350 K seafloor habitat and consume 10 mol s−1 of H2, the most probable biomass is 103, 103.7 kg C with ocean‐top pH 8,9, respectively. Biomass production consistent with space plume fluxes is 104–106 kgC yr−1—milligrams of cellular carbon per kilogram of H2O ejected—but requires that >50% of the space plume methane is biotic. Alternative scenarios are presented, and biomass is generally lower when habitat temperature is higher. Ocean biomass density cannot yet be reliably estimated owing to uncertainties in the scale and physicochemical properties of Enceladus' putative habitats. Evaluating abiotic to biotic ratios in plume methane and organic material could help identify false negative results from life detection missions and constrain the scale of an underlying biosphere. Plain Language Summary: The Cassini spacecraft observed energy and nutrient sources for life erupting from a water ocean below the icy exterior of Saturn's moon Enceladus. Future spacecraft planned for Enceladus, Europa and Titan will obtain similar measurements in greater detail. In this work, we calculate the probability that different suites of environments inside Enceladus' ocean are habitable for methanogens, an ancient type of organism which may be able to survive there. Three scenarios are possible: uninhabitable, habitable, and energy‐saturated. Next, we extend this calculation to show that the possible biosphere is small but productive. Microbial waste, generated at the seafloor, could be ejected from the ocean and consequently snow down onto Enceladus' surface. Mass spectrometers on future spacecraft could constrain these possibilities further and may be critical to inferring biosignatures when cell densities are too low to detect. Key Points: Spatial habitability on Enceladus is not guaranteed, and additional modeling parameters are needed to evaluate possible vacant habitatsCell turnover is important for life detection missions and can be constrained more tightly than total biomassAbiotic to biotic ratios of space plume carbon are critical as biosignatures and for assessing the scale of Enceladus' notional biosphere [ABSTRACT FROM AUTHOR]

The integration of biology and spacefaring has led to the development of three interrelated fields: Astrobiology, Bioastronautics, and Space Bioprocess Engineering. Astrobiology is concerned with the study of the origin, evolution, distribution, and future of life in the universe, while Bioastronautics focuses on the effects of spaceflight on biological systems, including human physiology and psychology. Space Bioprocess Engineering, on the other hand, deals with the design, deployment, and management of biotechnology for human exploration. This paper highlights the unique contributions of each field and outlines opportunities for biologists to engage in these exciting avenues of research. By providing a clear overview of the major fields of biology and spacefaring, this paper serves as a valuable resource for scientists and researchers interested in exploring the integration of these disciplines. [ABSTRACT FROM AUTHOR]