Organic Input to Titan's Subsurface Ocean Through Impact Cratering.

Titan has an organic-rich atmosphere and surface with a subsurface liquid water ocean that may represent a habitable environment. In this work, we determined the amount of organic material that can be delivered from Titan's surface to its ocean through impact cratering. We assumed that Titan's craters produce impact melt deposits composed of liquid water that can founder in its lower-density ice crust and estimated the amount of organic molecules that could be incorporated into these melt lenses. We used known yields for HCN and Titan haze hydrolysis to determine the amount of glycine produced in the melt lenses and found a range of possible flux rates of glycine from the surface to the subsurface ocean. These ranged from 0 to 1011 mol/Gyr for HCN hydrolysis and from 0 to 1014 mol/Gyr for haze hydrolysis. These fluxes suggest an upper limit for biomass productivity of ∼103 kgC/year from a glycine fermentation metabolism. This upper limit is significantly less than recent estimates of the hypothetical biomass production supported by Enceladus's subsurface ocean. Unless biologically available compounds can be sourced from Titan's interior, or be delivered from the surface by other mechanisms, our calculations suggest that even the most organic-rich ocean world in the Solar System may not be able to support a large biosphere.

Future of the Search for Life: Workshop Report.

The 2-week, virtual Future of the Search for Life science and engineering workshop brought together more than 100 scientists, engineers, and technologists in March and April 2022 to provide their expert opinion on the interconnections between life-detection science and technology. Participants identified the advances in measurement and sampling technologies they believed to be necessary to perform in situ searches for life elsewhere in our Solar System, 20 years or more in the future. Among suggested measurements for these searches, those pertaining to three potential indicators of life termed "dynamic disequilibrium," "catalysis," and "informational polymers" were identified as particularly promising avenues for further exploration. For these three indicators, small breakout groups of participants identified measurement needs and knowledge gaps, along with corresponding constraints on sample handling (acquisition and processing) approaches for a variety of environments on Enceladus, Europa, Mars, and Titan. Despite the diversity of these environments, sample processing approaches all tend to be more complex than those that have been implemented on missions or envisioned for mission concepts to date. The approaches considered by workshop breakout groups progress from nondestructive to destructive measurement techniques, and most involve the need for fluid (especially liquid) sample processing. Sample processing needs were identified as technology gaps. These gaps include technology and associated sampling strategies that allow the preservation of the thermal, mechanical, and chemical integrity of the samples upon acquisition; and to optimize the sample information obtained by operating suites of instruments on common samples. Crucially, the interplay between science-driven life-detection strategies and their technological implementation highlights the need for an unprecedented level of payload integration and extensive collaboration between scientists and engineers, starting from concept formulation through mission deployment of life-detection instruments and sample processing systems.

Feasibility of Remote Unsupervised Cognitive Screening With SATURN in Older Adults.

Widespread cognitive test screening as part of tele-public health initiatives necessitates a test that is self-administered online and automatically scored, with no clinician effort. The feasibility of unsupervised cognitive screening is unclear. We adapted the Self-Administered Tasks Uncovering Risk of Neurodegeneration (SATURN) to make it suitable for self-administration and automatic scoring. A sample of 364 healthy older adults completed SATURN via a web browser, in a fully independent manner. SATURN's overall score was not modulated by gender, education, reading speed, the time of day at which the test was taken, or an individual's familiarity with technology. SATURN proved extremely portable across operating systems. Importantly, comments from participants reported satisfaction with the experience and the clarity of the instructions. SATURN represents a fast and easy screening tool that can be used for a first assessment, during a routine test or clinical evaluation, or during periodic health monitoring, in person or remotely.

Selection and Analytical Performances of the Dragonfly Mass Spectrometer Gas Chromatographic Columns to Support the Search for Organic Molecules of Astrobiological Interest on Titan.

Titan is a key planetary body for astrobiology, with the presence of a subsurface ocean and a dense atmosphere, in which complex chemistry is known to occur. Approximately 1-Titan-year after the Cassini-Huygens mission arrived in the saturnian system, Dragonfly rotorcraft will land on Titan's surface by 2034 for an exhaustive geophysical and chemical investigation of the Shangri-La organic sand sea region. Among the four instruments onboard Dragonfly, the Dragonfly Mass Spectrometer (DraMS) is dedicated to analyze the chemical composition of surface samples and noble gases in the atmosphere. One of the DraMS analysis modes, the Gas Chromatograph-Mass Spectrometer (GC-MS), is devoted to the detection and identification of organic molecules that could be involved in the development of a prebiotic chemistry or even representative of traces of past or present life. Therefore, DraMS-GC subsystem should be optimized to detect and identify relevant organic compounds to meet this objective. This work is focused on the experimental methods employed to select the chromatographic column to be integrated in DraMS-GC, to assess the analytical performances of the column selected, and also to assess the performances of the second DraMS-GC column, which is devoted to the separation of organic enantiomers. Four different stationary phases have been tested to select the most relevant one for the separation of the targeted chemical species. The results show that the stationary phase composed of polymethyl (95%) diphenyl (5%) siloxane is the best compromise in terms of efficiency, robustness, and retention times of the molecules. The combination of the general and the chiral columns in DraMS is perfectly suited to in situ chemical analysis on Titan and for the detection of expected diverse and complex organic compounds.

How Saturn got its tilt and its rings.

The destruction of a hypothetical moon may help explain the origin of both.

Survival strategies of an anoxic microbial ecosystem in Lake Untersee, a potential analog for Enceladus.

Lake Untersee located in Eastern Antarctica, is a perennially ice-covered lake. At the bottom of its southern basin lies 20 m of anoxic, methane rich, stratified water, making it a good analog for Enceladus, a moon of Saturn. Here we present the first metagenomic study of this basin and detail the community composition and functional potential of the microbial communities at 92 m, 99 m depths and within the anoxic sediment. A diverse and well-populated microbial community was found, presenting the potential for Enceladus to have a diverse and abundant community. We also explored methanogenesis, sulfur metabolism, and nitrogen metabolism, given the potential presence of these compounds on Enceladus. We found an abundance of these pathways offering a variety of metabolic strategies. Additionally, the extreme conditions of the anoxic basin make it optimal for testing spaceflight technology and life detection methods for future Enceladus exploration.

Science Objectives for Flagship-Class Mission Concepts for the Search for Evidence of Life at Enceladus.

Cassini revealed that Saturn's Moon Enceladus hosts a subsurface ocean that meets the accepted criteria for habitability with bio-essential elements and compounds, liquid water, and energy sources available in the environment. Whether these conditions are sufficiently abundant and collocated to support life remains unknown and cannot be determined from Cassini data. However, thanks to the plume of oceanic material emanating from Enceladus' south pole, a new mission to Enceladus could search for evidence of life without having to descend through kilometers of ice. In this article, we outline the science motivations for such a successor to Cassini, choosing the primary science goal to be determining whether Enceladus is inhabited and assuming a resource level equivalent to NASA's Flagship-class missions. We selected a set of potential biosignature measurements that are complementary and orthogonal to build a robust case for any life detection result. This result would be further informed by quantifications of the habitability of the environment through geochemical and geophysical investigations into the ocean and ice shell crust. This study demonstrates that Enceladus' plume offers an unparalleled opportunity for in situ exploration of an Ocean World and that the planetary science and astrobiology community is well equipped to take full advantage of it in the coming decades.

Technology's Palette: Voyager's Eyes and the Hyperchromatic Enhancement of Jupiter and Saturn.

In the late 1970s and early 1980s, NASA's Voyager mission offered the first clear pictures of Jupiter and Saturn. These images show the planets in strikingly brilliant, recognizably engineered, psychedelic colors: technology's palette. The use of color was justified on epistemological grounds; it made visible scientifically compelling features. But color palette also has a history, one that has not been previously considered. This article takes up this history and adds to the literature on the visual culture of science. It establishes that the Jet Propulsion Laboratory's pioneering role in digital image processing, the color conventions adopted for representing Earth, and American counterculture of the 1960s and its attitudes toward technology together created the conditions that allowed for hyperchromatic views of the planets. Technology's palette enhanced the scientific understanding of Jupiter and Saturn, while simultaneously celebrating technologically enhanced vision and the promise of seeing by means of humanmachine collaborations.

Quantitative evaluation of the feasibility of sampling the ice plumes at Enceladus for biomarkers of extraterrestrial life.

Enceladus, an icy moon of Saturn, is a compelling destination for a probe seeking biosignatures of extraterrestrial life because its subsurface ocean exhibits significant organic chemistry that is directly accessible by sampling cryovolcanic plumes. State-of-the-art organic chemical analysis instruments can perform valuable science measurements at Enceladus provided they receive sufficient plume material in a fly-by or orbiter plume transit. To explore the feasibility of plume sampling, we performed light gas gun experiments impacting micrometer-sized ice particles containing a fluorescent dye biosignature simulant into a variety of soft metal capture surfaces at velocities from 800 m ⋅ s-1 up to 3 km ⋅ s-1 Quantitative fluorescence microscopy of the capture surfaces demonstrates organic capture efficiencies of up to 80 to 90% for isolated impact craters and of at least 17% on average on indium and aluminum capture surfaces at velocities up to 2.2 km ⋅ s-1 Our results reveal the relationships between impact velocity, particle size, capture surface, and capture efficiency for a variety of possible plume transit scenarios. Combined with sensitive microfluidic chemical analysis instruments, we predict that our capture system can be used to detect organic molecules in Enceladus plume ice at the 1 nM level-a sensitivity thought to be meaningful and informative for probing habitability and biosignatures.

Investigation of Venus Cloud Aerosol and Gas Composition Including Potential Biogenic Materials via an Aerosol-Sampling Instrument Package.

A lightweight, low-power instrument package to measure, in situ, both (1) the local gaseous environment and (2) the composition and microphysical properties of attendant venusian aerosols is presented. This Aerosol-Sampling Instrument Package (ASIP) would be used to explore cloud chemical and possibly biotic processes on future aerial missions such as multiweek balloon missions and on short-duration (<1 h) probes on Venus and potentially on other cloudy worlds such as Titan, the Ice Giants, and Saturn. A quadrupole ion-trap mass spectrometer (QITMS; Madzunkov and Nikolic, J Am Soc Mass Spectrom 25:1841-1852, 2014) fed alternately by (1) an aerosol separator that injects only aerosols into a vaporizer and mass spectrometer and (2) the pure aerosol-filtered atmosphere, achieves the compositional measurements. Aerosols vaporized <600°C are measured over atomic mass ranges from 2 to 300 AMU at <0.02 AMU resolution, sufficient to measure trace materials, their isotopic ratios, and potential biogenic materials embedded within H2SO4 aerosols, to better than 20% in <300 s for H2SO4 -relative abundances of 2 × 10-9. An integrated lightweight, compact nephelometer/particle-counter determines the number density and particle sizes of the sampled aerosols.

Theoretical Constraints Imposed by Gradient Detection and Dispersal on Microbial Size in Astrobiological Environments.

The capacity to sense gradients efficiently and acquire information about the ambient environment confers many advantages such as facilitating movement toward nutrient sources or away from toxic chemicals. The amplified dispersal evinced by organisms endowed with motility is possibly beneficial in related contexts. Hence, the connections between information acquisition, motility, and microbial size are explored from an explicitly astrobiological standpoint. By using prior theoretical models, the constraints on organism size imposed by gradient detection and motility are elucidated in the form of simple heuristic scaling relations. It is argued that environments such as alkaline hydrothermal vents, which are distinguished by the presence of steep gradients, might be conducive to the existence of "small" microbes (with radii of ≳0.1 µm) in principle, when only the above two factors are considered; other biological functions (e.g., metabolism and genetic exchange) could, however, regulate the lower bound on microbial size and elevate it. The derived expressions are potentially applicable to a diverse array of settings, including those entailing solvents other than water; for example, the lakes and seas of Titan. The article concludes with a brief exposition of how this formalism may be of practical and theoretical value to astrobiology.

Plausible Emergence of Biochemistry in Enceladus Based on Chemobrionics.

Saturn's satellite Enceladus is proposed to have a soda-type subsurface ocean with temperature able to support life and an iron ore-based core. Here, it was demonstrated that ocean chemistry related to Enceladus can support the development of Fe-based hydrothermal vents, one of the places suggested to be the cradle of life. The Fe-based chemical gardens were characterized with Fourier-transform (FT)IR spectroscopy and XRD. The developed chemobrionic structures catalyzed the condensation polymerization of simple organic prebiotic molecules to kerogens. Further, they could passively catalyze the condensation of the prebiotic molecule formamide to larger polymers, suggesting that elementary biochemical precursors could have emerged in Enceladus.

Viability of Bacillus subtilis Spores Exposed to Ultraviolet Light at Ocean World Surface Temperatures.

This work investigated microorganism survival under temperature and ultraviolet (UV) radiation conditions found at the surface of ice-covered ocean worlds. These studies were motivated by a desire to understand the ability of resilient forms of life to survive under such conditions as a proxy for potential endogenic life and to inform planetary protection protocols for future missions. To accomplish this, we irradiated Bacillus subtilis spores with solar-like UV photons at temperatures ranging from room temperature down to 11 K and reported survival fractions with respect to fluence. We observed an increase in survival at low temperatures and found that the inactivation rate follows an Arrhenius-type behavior above 60 K. For solar-photon fluxes and surface temperatures at Europa and Enceladus, we found that Bacillus subtilis spores would be inactivated in less than an hour when in direct sunlight.

Exo-Ocean Exploration with Deep-Sea Sensor and Platform Technologies.

One of Saturn's largest moons, Enceladus, possesses a vast extraterrestrial ocean (i.e., exo-ocean) that is increasingly becoming the hotspot of future research initiatives dedicated to the exploration of putative life. Here, a new bio-exploration concept design for Enceladus' exo-ocean is proposed, focusing on the potential presence of organisms across a wide range of sizes (i.e., from uni- to multicellular and animal-like), according to state-of-the-art sensor and robotic platform technologies used in terrestrial deep-sea research. In particular, we focus on combined direct and indirect life-detection capabilities, based on optoacoustic imaging and passive acoustics, as well as molecular approaches. Such biologically oriented sampling can be accompanied by concomitant geochemical and oceanographic measurements to provide data relevant to exo-ocean exploration and understanding. Finally, we describe how this multidisciplinary monitoring approach is currently enabled in terrestrial oceans through cabled (fixed) observatories and their related mobile multiparametric platforms (i.e., Autonomous Underwater and Remotely Operated Vehicles, as well as crawlers, rovers, and biomimetic robots) and how their modified design can be used for exo-ocean exploration.

What Is Life-and When Do We Search for It on Other Worlds.

There has been considerable attention on how to detect life on other worlds by searching for biomolecules. However, there has been much less clarity as to when it becomes warranted to focus a mission on the search for life on another world. At a minimum, a life-detection mission should follow convincing evidence of (1) Liquid water of suitable salinity, past or present; (2) Carbon in the water; (3) Biologically available N in the water; (4) Biologically useful energy in the water; (5) Organic material that can possibly be of biological origin and a plausible strategy for sampling this material. Based on these prerequisites, the most promising targets for a life search are currently the plume of Enceladus and the subsurface of Mars-in equatorial lake bed sediments and in polar ice-cemented ground. Neither the surface of Europa nor the clouds of Venus meet the criteria listed here but may with further exploration.

Detection of Organic Matter and Biosignatures in Space Missions.

Carbon-based compounds are widespread throughout the Universe, including abiotic molecules that are the components of the life as we know it. This article reviews the space missions that have aimed to detect organic matter and biosignatures in planetary bodies of our solar system. While to date there was only one life-detection space mission, i.e., the Viking mission to Mars, several past and present space missions have searched for organic matter, paving the way for the future detection of signatures of extra-terrestrial life. This review also reports on the in-situ analysis of organic matter and sample-return missions from primitive bodies, i.e. comets and asteroids, providing crucial information on the conditions of the early solar system as well as on the building blocks of life delivered to the primitive Earth.

A never-ending story in the sky: The secrets of chemical evolution.

Cosmic evolution is the tale of progressive transition from simplicity to complexity. The newborn universe started with the simplest atoms formed after the Big Bang and proceeded toward the formation of the so-called 'astronomical complex organic molecules' (aCOMs), most of them showing a clear prebiotic character. Understanding the chemical evolution of the universe is one of the main aims of Astrochemistry, with the starting point being the knowledge whether a molecule is present in the astronomical environment under consideration and, if so, its abundance. However, the interpretation of astronomical detections and the identification of molecules are not at all straightforward. Indeed, the extraterrestrial chemical inventory has been obtained by means of astronomical observations based on spectroscopic signatures determined in laboratory (either experimental or computational) studies. Even though the presence of aCOMs has been known for decades, the processes that lead to their synthesis are still hotly debated or even unknown. It is often assumed that aCOMs are mostly synthesized on grain surfaces during the so-called warm-up phase, when various radicals trapped in the grain mantles acquire mobility and recombine into large molecules. However, recent detections of aCOMs in cold environments have challenged this exclusive role of grain-surface chemistry. Clearly, gas-phase chemistry is at work in cold environments. Moving to Titan's atmosphere, prior to the Cassini-Huygens arrival in the Saturn system, it was generally believed that Earth and interstellar space are the two places where organic molecules are/were synthesized extensively. However, the experimental measurements by the instruments on board the Cassini orbiter spacecraft and the Huygens probe lander have changed this view. To disclose the "secrets" of chemical evolution across space, the first step is the understanding of how small prebiotic species are formed and how the chemical complexity can further increase. This review indeed addresses the chemical evolution in space, focusing - in particular - on the role played by molecular spectroscopy and quantum-chemical computations. To summarize, in this review we will first of all present how the signatures of molecules can be found in space. Then, we will address, from a computational point of view, the derivation of the molecular spectroscopic features, the investigation of gas-phase formation routes of prebiotic species in the ISM, and the evolution of chemical complexity, from small molecules to haze, in Titan's atmosphere. Finally, an integrated strategy, also involving high-performance computers and virtual reality, will be discussed.

Analog Experiments for the Identification of Trace Biosignatures in Ice Grains from Extraterrestrial Ocean Worlds.

Reliable identification of biosignatures, such as amino acids, fatty acids, and peptides, on extraterrestrial ocean worlds is a key prerequisite for space missions that search for life or its emergence on these worlds. One promising approach is the use of high-performance in situ impact ionization mass spectrometers to sample water ice grains emerging from ocean-bearing moons such as Europa or Enceladus. A predecessor of such detectors, the Cosmic Dust Analyzer on board the Cassini spacecraft, has proven to be very successful in analyzing inorganic and organic ocean constituents and with that characterizing the habitability of Enceladus ocean. However, biosignatures have not been definitively identified in extraterrestrial ocean environments so far. Here, we investigate with an analog experiment the spectral appearance of amino acids, fatty acids, and peptides in water ice grains, together with their detection limits, as applicable to spaceborne mass spectrometers. We employ a laboratory-based laser induced liquid beam ion desorption technique, proven to simulate accurately the impact ionization mass spectra of water ice grains over a wide range of impact speeds. The investigated organics produce characteristic mass spectra, with molecular peaks as well as clearly identifiable, distinctive fragments. We find the detection limits of these key biosignatures to be at the µM or nM level, depending on the molecular species and instrument polarity, and infer that impact ionization mass spectrometers are most sensitive to the molecular peaks of these biosignatures at encounter velocities of 4-6 km/s.

Protein Stability in Titan's Subsurface Water Ocean.

Models of Titan predict that there is a subsurface ocean of water and ammonia under a layer of ice. Such an ocean would be important in the search for extraterrestrial life since it provides a potentially habitable environment. To evaluate how Earth-based proteins would behave in Titan's subsurface ocean environment, we used molecular dynamics simulations to calculate the properties of proteins with the most common secondary structure types (alpha helix and beta sheet) in both Earth and Titan-like conditions. The Titan environment was simulated by using a temperature of 300 K, a pressure of 1000 bar, and a eutectic mixture of water and ammonia. We analyzed protein compactness, flexibility, and backbone dihedral distributions to identify differences between the two environments. Secondary structures in the Titan environment were found to be less long-lasting, less flexible, and had small differences in backbone dihedral preferences (e.g., in one instance a pi helix formed). These environment-driven differences could lead to changes in how these proteins interact with other biomolecules and therefore changes in how evolution would potentially shape proteins to function in subsurface ocean environments.