Ocean Worlds Research Articles

Recent work on indenture in the British World

AbstractThis article provides an overview of the historiography of indentured labor in the 18th and 19th centuries, along with a brief narrative of the origin and definition of indenture. It traces the evolution of the history of indenture in the “British World” (defined here as the areas under both formal and informal British imperial control) from a neglected field to a major focus of historical study. The final section summarizes the current state of the field, assessing how it has moved beyond its earlier focus on social history, demographics, and diaspora studies to become an entry point for wider discussions about the history of imperialism and colonialism, the global history of capitalism, and the history of networks and exchanges between the Atlantic, Pacific, and Indian Ocean Worlds.

Effects of salts on the exchanges through high-pressure ice layers of large ocean worlds

The habitability of large icy moons has long been disputed due to the presence of an high-pressure (HP) ice layer located between the core and the internal liquid ocean, preventing a direct contact and facilitated exchanges between both. In our previous study (Lebec et al. 2023), we have shown that under certain conditions and considering the phase change at the upper boundary of the HP ice shell, heat and mass transfer can occur and be efficient. Now, the aim of this work is to study the effects of impurities inside the HP ices on the flow dynamics and the mass transfer efficiency from the core to the ocean. These salts can enter the ice layer either by diffusion, which is a very inefficient process, or by partial melting at the bottom of the ice layer, if the temperature is high enough. In that case, the liquid water can interact with the core and get enriched in salts. This salty water, which can be lighter than high-pressure ices, could rise through the ice shell and refreeze. The resulting salts/ice mixture can be transported into the ocean by convection in the solid state but could also impede it due to its density higher than that of pure ice. The efficiency of convection depends on the buoyancy number Bsalts, which is the ratio of density increase associated to salts compared to the decrease associated to temperature. To explore the impact of salts, we model a flux of salts from the core and the advection of these salts using Lagrangian tracers in order to study the effects of the Rayleigh number, the buoyancy number and K, which is the partition coefficient of the salts between the ocean and the HP ices at the top interface, on the heat and salts transfer efficiency through the HP ice layer, as well as the implications for the evolution of salt concentration in the ocean of large icy moons and ocean worlds. We present a scaling of the bottom temperature and the top radial velocity wtop as function of the Rayleigh number Raq for various values of the buoyancy number and a scaling of the effective flux of salts across the top interface with the ocean as function of the buoyancy number for various values of the partition coefficient. We perform a numerical application for Ganymede and show that depending on the values of the system parameters, a significant percentage of the salts entering the HP ice layer from the core can efficiently flow into the ocean.

Energy yields for acetylenotrophy on Enceladus and Titan

Saturn's moons Titan and Enceladus appear to satisfy three key criteria for life: presence of liquid water, nutrient availability, and metabolic energy sources. Consequently, these ocean worlds are the focus of astrobiology research investigations that aim to assess the potential for life beyond Earth. One plausible source of metabolic energy on these moons is acetylene (C2H2), a simple organic compound that is the second most abundant photochemical product in Titan's atmosphere and has been identified as a likely constituent of Enceladus' ocean. Acetylenotrophy, or the microbial fermentation of acetylene, is utilized by microbes on Earth in a number of environments. Here, we have calculated the energy yield of acetylenotrophy to be 69–78 kJ/mol C within the oceans of Titan and Enceladus, greater than the widely considered, hydrogenotrophic methanogenesis, at 25–65 kJ/mol C. Therefore, we propose acetylenotrophy as a potential metabolism on these moons that should be considered in future astrobiology studies on worlds with abundant acetylene.

Onboard Science Instrument Autonomy for the Detection of Microscopy Biosignatures on the Ocean Worlds Life Surveyor

The quest to find extraterrestrial life is a critical scientific endeavor with civilization-level implications. Icy moons in our solar system are promising targets for exploration because their liquid oceans make them potential habitats for microscopic life. However, the lack of a precise definition of life poses a fundamental challenge to formulating detection strategies. To increase the chances of unambiguous detection, a suite of complementary instruments must sample multiple independent biosignatures (e.g., composition, motility/behavior, and visible structure). Such an instrument suite could generate 10,000× more raw data than is possible to transmit from distant ocean worlds like Enceladus or Europa. To address this bandwidth limitation, Onboard Science Instrument Autonomy (OSIA) is an emerging discipline of flight systems capable of evaluating, summarizing, and prioritizing observational instrument data to maximize science return. We describe two OSIA implementations developed as part of the Ocean World Life Surveyor (OWLS) prototype instrument suite at the Jet Propulsion Laboratory. The first identifies life-like motion in digital holographic microscopy videos, and the second identifies cellular structure and composition via innate and dye-induced fluorescence. Flight-like requirements and computational constraints were used to lower barriers to infusion, similar to those available on the Mars helicopter, “Ingenuity.” We evaluated the OSIA's performance using simulated and laboratory data and conducted a live field test at the hypersaline Mono Lake planetary analog site. Our study demonstrates the potential of OSIA for enabling biosignature detection and provides insights and lessons learned for future mission concepts aimed at exploring the outer solar system.

Transnational Queer Materialism

The introduction to this special issue takes up the narrations and values produced by the travels of words like queer of color, race, and racial capitalism to both comobilize and retheorize queer of color critique and the content and contours of global racial capitalism. With and beyond the story of US empire and the transatlantic slave trade—from peripheral European engagements with Africa to the circulation of caste in Africa via Indian Ocean worlds—in this special issue the authors examine some of the histories and present modes of capitalist accumulation that are relevant to telling global stories of race and capitalism. A queer/trans lens keeps the authors’ attention trained as well on the arrangements and estrangements of the sex/gender systems that power such narratives of race and capitalism. So positioned, the authors enter ongoing debates on the geopolitics of queer studies, the import of queer materialism, and theorizations of racial capitalism by asking (1) What is the “racial” of racial capitalism?, and (2) What is the “of color” in queer/trans of color critique? The questions form a method for thinking global racial capitalism and queer/trans of color study together—what the authors call transnational queer materialism.

Water content of rocky exoplanets in the habitable zone

In this study we investigated the interiors of rocky exoplanets in order to identify those that may have large quantities of water. We modelled the interiors of 28 rocky exoplanets, assuming four different layers – an iron core, a rock mantle, a high-pressure ice layer, and a surface ice/water layer. Due to observational bias, our study is limited to habitable zone exoplanets. We determined a range of possible water mass fractions for each planet consistent with the modelled planetary structures. We calculated the tidal heating experienced by these exoplanets through gravitational interactions with their host stars, assuming a temperature- and composition-dependent Maxwell viscoelastic rheology. Assuming radioactive elemental abundances observed in Solar System meteorites, we also calculated the radiogenic heat flux inside the planets. We estimated the probability of the presence of a thick ocean layer in these planets, taking into account the effect of both tidal and radiogenic heating. Our results showed that Proxima Centauri b, Ross 128 b, Teegarden’s b and c, GJ 1061 c and d, and TRAPPIST-1 e may have an extended liquid water reservoir. Furthermore, extremely high H2O-content of the exoplanets Kepler-62 f, Kepler-1652 b, Kepler-452 b, and Kepler-442 b suggests that these planets may maintain a water vapour atmosphere and may in fact be examples of larger ocean worlds. Upon the discovery of new rocky exoplanets beyond the habitable zone, our study can be extended to icy worlds.

Green with Envy: Celadons, Circulation, and Emulation in the Red Sea, Persian Gulf and Indian Ocean Worlds

Much scholarship concerning the maritime ceramic-exchange networks between China and the Red Sea, Persian Gulf, and Indian Ocean worlds has concentrated on the importation of Chinese blue-and-white porcelains and local responses to these wares. Celadon ceramics, however, were among the earliest Chinese wares to be traded—and emulated—within these exchange systems. Foregrounding examples from the collection of the Freer Gallery of Art at the Smithsonian’s National Museum of Asian Art, this article will consider textual evidence, manuscript paintings, archaeological finds, and extant objects, in order to explore the reception and emulation of Chinese celadon ceramics within these regions, with a focus on West Asia. Cutting across previously published, somewhat siloed studies, the discussion will place these celadon-exchange histories into a broader framework, tracing varying responses toward these materials in the context of transregional geographies.

Can one hear supercontinents in the tides of ocean planets?

Context.Recent observations and theoretical progress made about the history of the Earth-Moon system suggest that tidal dissipation in oceans primarily drives the long-term evolution of orbital systems hosting ocean planets. Particularly, they emphasise the key role played by the geometry of land-ocean distributions in this mechanism. However, the complex way continents affect oceanic tides still remains to be elucidated.Aims.In the present study, we investigate the impact of a single supercontinent on the tidal response of an ocean planet and the induced tidally dissipated energy.Methods.The adopted approach is based on the linear tidal theory. By simplifying the continent to a spherical cap of a given angular radius and position on the globe, we carried out a harmonic analysis of the whole planet’s tidal response including the coupling with the solid part due to ocean loading and self-attraction variations. In this framework, tidal flows are formulated analytically in terms of explicitly defined oceanic eigenmodes, as well as the resulting tidal Love numbers, dissipated power, and torque.Results.The analysis highlights the symmetry breaking effect of the continent, which makes the dependence of tidal quantities on the tidal frequency become highly irregular. The metric introduced to quantify this continentality effect reveals abrupt transitions between polar and non-polar configurations, and between small-sized and medium-sized continents. Additionally, it predicts that a continent similar to South America or smaller (~30° angular radius) does not qualitatively alter the tidal response of a global ocean regardless of its position on the planet.

Surface Volatile Composition as Evidence for Hydrothermal Processes Lasting Longer in Triton’s Interior than Pluto’s

Ocean worlds, or icy bodies in the outer solar system that have or once had subsurface liquid water oceans, are among the most compelling topics of astrobiology. Typically, confirming the existence of a subsurface ocean requires close spacecraft observations. However, combining our understanding of the chemistry that takes place in a subsurface ocean with our knowledge of the building blocks that formed potential ocean worlds provides an opportunity to identify tracers of endogenic activity in the surface volatiles of Pluto and Triton. We show here that the current composition of the volatiles on the surfaces and in the atmospheres of Pluto and Triton are deficient in carbon, which can only be explained by the loss of CH4 through a combination of aqueous chemistry and atmospheric processes. Furthermore, we find that the relative nitrogen and water abundances are within the range observed in building block analogs, comets, and chondrites. A lower limit for N/Ar in Pluto’s atmosphere also suggests source building blocks that have a cometary or chondritic composition, all pointing to an origin for their nitrogen as NH3 or organics. Triton’s lower abundance of CH4 compared to Pluto, and the detection of CO2 at Triton but not at Pluto points to aqueous chemistry in a subsurface ocean that was more efficient at Triton than Pluto. These results have applications to other large Kuiper Belt objects as well as the assessment of formation locations and times for the four giant planets given future probe measurements of noble gas abundances and isotope ratios.

On the More Complex Wavelength Dependency of Airy Isostasy in Icy Shells of Ocean Worlds

AbstractThe topography of ocean worlds is often used to infer ice shell thicknesses by assuming topography is compensated by a basal root. We systematically test the stability of isostatically compensated topography in ice shells. At short horizontal wavelengths, lithospheric strength can support surface topography, while at long wavelengths, buoyancy forces can support topography at the surface and base of the ice shell over geologic time scales. These behaviors are also seen for Airy isostasy in terrestrial worlds. Contrastingly at intermediate scales, the mechanically weak lower ice shell can inhibit the transfer of buoyancy forces to the surface. Factors such as surface temperature can alter the contribution of lithospheric strength, decreasing the stability of a compensating root. This nuanced understanding of icy shell lithospheres provides crucial insights for interpreting surface features and inferring underlying ice shell thickness, with substantial relevance for upcoming space missions to the Jovian system.

Variable Salinity and Hydrogen Production in Europa's Ocean

AbstractEuropa's long‐term habitability depends on thermodynamics—modulated by tidal evolution—and geochemical pathways that define chemical and energy inventories for use by putative biology. Hydrogen produced from the reaction of water and rock during serpentinization is one potential source of metabolic energy. Here, we demonstrate how thermally modulated volumetric changes to Europa's ice shell, ocean, and fluid‐accessible rocky mantle influence oceanic salinity and serpentinization rates in Europa's interior. During periods of steady cooling, hydrogen flux into the ocean remains relatively constant because of the continuous propagation of thermal cracking into the rocky mantle regardless of ocean composition. However, during periods of fluctuating heat production driven by changes in orbital eccentricity, modulation of the ice shell volume, and consequently the salinity and water activity of the ocean, alters the serpentinization rate. In parallel, the extent of fracturing within the seafloor varies, changing the volume of reactable rock available. Our results show that the stability of serpentinization reactions on Europa over time highly depends on the thermal‐orbital evolution and oceanic salt content. The variability in the hydrogen production rate is significant across potential orbital histories, varying by up to 15 orders of magnitude for the lowest salinity and most kosmotropic ocean conditions, such as dilute MgSO4 compositions. We also show that this variability decreases with increasing ocean salinity and more chaotropic compositions, such as a concentrated NaCl ocean. These results suggest new ways that ocean composition and water activity are essential to stable habitable conditions in ocean worlds.

Divergent Behavior of Hydrothermal Plumes in Fresh Versus Salty Icy Ocean Worlds

AbstractWater parcels close to their freezing point contract and become heavy on warming if they are sufficiently fresh (salinity less than 22g kg−1 for earth's ocean), but expand and become buoyant when salty (salinity greater than 22g kg−1). We explore the resulting divergent behavior of hydrothermal plumes in fresh versus salty icy ocean worlds, with particular emphasis on Europa and Enceladus. Large, salty, putative Europa‐like oceans, develop buoyant plumes which rise upwards in the water column when energized by localized hydrothermal vents. Instead, small, fresher, putative Enceladus‐like oceans, can develop bottom‐hugging gravity currents when heated near the freezing point, due to the anomalous contraction of fluid parcels on warming. Such a bottom‐filling regime would most likely be a transient stage in the evolution of an icy moon over geological time. The contrasting dynamics are highlighted and rationalized in terms of key non‐dimensional numbers with a focus on the ability of ocean to carry bio‐markers from the hydrothermal activity at the bottom to the ice shell at the top. Finally, the implications of our study for prioritizing future missions to icy moons are discussed. An advantage of a mission to a large icy moon (e.g., Europa), rather than a smaller target (e.g., Enceladus), is that a larger moon's ocean would likely support buoyant convection, which could bring signatures of seafloor venting to the outer ice‐shell regardless of that ocean's salinity. For smaller icy moons, the nature of convection would hinge on its assumed salinity.

Biosignature preparation for ocean worlds (BioPOW) instrument prototype

In situ sampling missions to detect biosignatures on ocean worlds requires thorough sample preparation to manage the expected chemical complexity of such environments. Proposed instruments must be capable of automatic liquid sample handling to ensure sensitive and accurate detections of biosignatures, regardless of the initial chemical composition. Herein, we outline the design, build, and test of the integrated Biosignature Preparation for Ocean Worlds (BioPOW) system capable of purifying amino acids from icy samples. This four step modular instrument 1) melts ice samples, 2) purifies amino acids via cation exchange chromatography, 3) concentrates via vacuum drying, and 4) derivatizes amino acids to volatilize and enable detection with downstream analytical instruments. Initial experiments validated the thermal performance of the system by melting ice in the sample cup (1 mL sample, 3°C–28°C, <5 min, 1.4 kJ) and heating the derivatization tank past the concentration temperature (20°C–60°C, 12 min, 3.6 kJ) to the derivatization temperature (60°C–90°C, 25 min, 7.5 kJ). Later experiments investigated important factors for automatic cation exchange using a design of experiments approach, and found that initial salt concentration, sample and eluate flow rates, and water wash volumes all play significant roles in reducing conductivity (1.1 x–6.7 x) while maintaining phenylalanine yields between 31% and 94%. The modules were then integrated into a 12 cm × 20 cm × 20 cm fieldable platform for analysis, and the maturation of this design for future spaceflight is discussed.

High-Performance Computational Method for an Extended Three-Coupled Korteweg–de Vries System

This paper calculates numerical solutions of an extended three-coupled Korteweg–de Vries system by the q-homotopy analysis transformation method (q-HATM), which is a hybrid of the Laplace transform and the q-homotopy analysis method. Multiple investigations inspecting planetary oceans, optical cables, and cosmic plasma have employed the KdV model, significantly contributing to its development. The uniqueness, convergence, and maximum absolute truncation error of this algorithm are demonstrated. A numerical simulation has been performed to validate the accuracy and validity of the proposed approach. With high accuracy and few algorithmic processes, this algorithm supplies a series solution in the form of a recursive relation.

Marine Cold Seeps As A Gateway Of Deep Subsurface Extremophiles To The Seafloor

In the Earth’s deep subsurface life is comprised exclusively of microorganisms, and estimates indicate 12-45% of the global prokaryotic biomass, on the order of 1029 microbes, is found in subseafloor sediments. Investigating how this enormous microbial biomass is maintained in the extreme habitats below seafloor is critical for understanding the rules of life in the deep biosphere. Furthermore, Earth’s subseafloor habitats often present analog environments detected in other planets such as the recently discovered “ocean worlds”, i.e., planetary bodies in our solar system which consist of large subsurface oceans including Saturn’s moons Titan and Enceladus and Jupiter’s moon Europa. Therefore, investigating life in and beneath Earth’s oceans remains at the forefront of the current astrobiological research endeavors. Despite the inhospitable nature of the subseafloor sedimentary realm, active microbial populations including bacteria capable of transforming into dormant endospores have been demonstrated to inhabit deeply buried anoxic sediments and oil reservoirs, permeable ocean crust, and around hydrothermal vents. These extreme habitats often remain physically connected to the seafloor by unique geological features such as marine cold seeps that transmit hydrocarbon-rich fluids originating in deep sediment layers. It remains unclear how fluid migration in cold seeps influence the composition of the seabed microbiome and if they transport deep subsurface life up to the surface. In this study, we addressed this knowledge gap by analyzing over 180 marine surficial sediments from the Gulf of Mexico and the Monterey Bay to assess whether hydrocarbon fluid migration serves as a mechanism for the dispersal of subsurface extremophiles and their introduction into the seabed via cold seeps. Seafloor samples were collected either by piston coring or ROV-operated push coring and were stored at -20°C upon collection. Presence of hydrocarbons in the piston core sediments wa characterized by gas chromatography mass spectrometry and fluorescence spectroscopy whereas gas seepage was determined in the ROV push cores by visual confirmation of gas bubbles emanating from the seafloor. Sediment microbiome composition was determined by high throughput 16S rRNA gene amplicon sequencing. Metabolic diversity was assessed via a genome-centric metagenomics approach aided by shotgun metagenomic sequencing of selected samples. Additionally, viable bacterial endospore communities were investigated from a subset of over 120 of the above samples by allowing endospore germination using a high-temperature incubation assay followed by amplicon sequencing. While 132 of the piston core sediments contained migrated liquid hydrocarbons, evidence of continuous advective transport of thermogenic alkane gases was observed in 11 sediments. Gas seeps harbored distinct microbial communities featuring bacteria and archaea that are well known inhabitants of deep biosphere sediments. Specifically, 25 distinct sequence variants within the bacterial lineages Atribacterota and Aminicenantia and the archaeal lineage Thermoprofundales occurred in significantly greater relative sequence abundance along with well-known seep-colonizing members of the bacterial genus Sulfurovum, in the gas-positive sediments. Metabolic predictions guided by metagenome-assembled genomes suggested these organisms are anaerobic heterotrophs capable of non-respiratory breakdown of organic matter, likely enabling them to inhabit energy-limited deep subseafloor ecosystems. In addition, eight different lineages of anaerobic bacterial endospores activated by sediment incubation assays were strongly associated with hydrocarbon-bearing sediments. These lineages were most closely related to Clostridiales previously detected in oil reservoirs from around the world. These results cumulatively point to petroleum geofluids as a vector for the advection-assisted upward dispersal of deep biosphere microbes from subsurface to surface environments, shaping the microbiome of cold seep sediments and providing a general mechanism for the maintenance of microbial diversity in the deep sea.

Using AI to Fine Tune the Search for Life

Using AI to Fine Tune the Search for Life

Prospects for Cryovolcanic Activity on Cold Ocean Planets

We have estimated total internal heating rates and depths to possible subsurface oceans for 17 planets that may be cold ocean planets, low-mass exoplanets with equilibrium surface temperatures and/or densities that are consistent with icy surfaces and a substantial H2O content. We have also investigated the potential for tidally driven cryovolcanism and exosphere formation on these worlds. Estimated internal heating rates from tidal and radiogenic sources are large enough that all planets in our study may harbor subsurface oceans, and their geological activity rates are likely to exceed the geological activity rates on Jupiter’s moon Europa. Several planets are likely to experience enhanced volcanic activity rates that exceed that of Io. Owing to their relatively thin ice shells and high rates of internal heating, Proxima Cen b and LHS 1140 b are the most favorable candidates for telescopic detection of explosive, tidally driven cryovolcanism. Estimates for thin ice shells on Proxima Cen b, LHS 1140 b, Trappist-1f, and several Kepler planets suggest that any H2O vented into space during explosive cryovolcanic eruptions on these worlds could be sourced directly from their subsurface oceans. Like the icy moons in our outer solar system, cold ocean planets may be astrobiologically significant worlds that harbor habitable environments beneath their icy surfaces. These possibilities should be considered during analyses of observational data for small exoplanets from current and upcoming telescopes and during planning for a future space telescope mission aimed at characterization of potentially habitable exoplanets (e.g., Habitable Worlds Observatory).

Detectability of Local Water Reservoirs in Europa's Surface Layer Under Consideration of Coupled Induction

AbstractThe icy moon Europa is a primary target for the study of ocean worlds. Its subsurface ocean is expected to be subject to asymmetries on global scales (tidal deformation) and local scales (chaos regions, fractures). Here, we investigate the possibility to magnetic sound local asymmetries by calculating the induced magnetic fields generated by a radially symmetric ocean and a small, spherical water reservoir between the ocean and Europa's surface. The consideration of two conductive bodies introduces non‐linear magnetic field coupling between them. We construct an analytical model to describe the coupling between two conductive bodies and calculate the induced fields within the parameter space of possible conductivity values and icy crust thicknesses. Given the plasma magnetic field perturbations, we find that a reservoir cannot be detected during a flyby at 25 km altitude using electromagnetic induction. Potential detection of liquid water reservoirs can be achieved by deploying magnetometers on Europa's surface, where one magnetometer is placed directly on the target region of interest and a second one in the nearby vicinity as reference to distinguish from global asymmetries. With this method, the smallest reservoir that can be detected has a radius of 8 km and a conductivity of 30 S/m. Larger reservoirs are resolvable at lower conductivities, with a 20 km reservoir requiring a conductivity of approximately 5 S/m.

Solid-State Single-Molecule Sensing with the Electronic Life-Detection Instrument for Enceladus/Europa (ELIE).

Growing evidence of the potential habitability of Ocean Worlds across our solar system is motivating the advancement of technologies capable of detecting life as we know it-sharing a common ancestry or physicochemical origin with life on Earth-or don't know it, representing a distinct emergence of life different than our one known example. Here, we propose the Electronic Life-detection Instrument for Enceladus/Europa (ELIE), a solid-state single-molecule instrument payload that aims to search for life based on the detection of amino acids and informational polymers (IPs) at the parts per billion to trillion level. As a first proof-of-principle in a laboratory environment, we demonstrate the single-molecule detection of the amino acid L-proline at a 10 μM concentration in a compact system. Based on ELIE's solid-state quantum electronic tunneling sensing mechanism, we further propose the quantum property of the HOMO-LUMO gap (energy difference between a molecule's highest energy-occupied molecular orbital and lowest energy-unoccupied molecular orbital) as a novel metric to assess amino acid complexity. Finally, we assess the potential of ELIE to discriminate between abiotically and biotically derived α-amino acid abundance distributions to reduce the false positive risk for life detection. Nanogap technology can also be applied to the detection of nucleobases and short sequences of IPs such as, but not limited to, RNA and DNA. Future missions may utilize ELIE to target preserved biosignatures on the surface of Mars, extant life in its deep subsurface, or life or its biosignatures in a plume, surface, or subsurface of ice moons such as Enceladus or Europa. One-Sentence Summary: A solid-state nanogap can determine the abundance distribution of amino acids, detect nucleic acids, and shows potential for detecting life as we know it and life as we don't know it.

Oceans of Opportunity

Our solar system’s ocean worlds offer scientists intriguing instances of exotic phenomena and fresh prospects in the elusive search for planetary habitability.