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The Cassini mission provided evidence for a global subsurface ocean and ongoing hydrothermal activity on Enceladus, based on results from Cassini's mass spectrometers. Laboratory simulations of hydrothermal conditions on icy moons are needed to further constrain the composition of ejected ice grains containing hydrothermally altered organic material. Here, we present results from our newly established facility to simulate the processing of ocean material within the temperature range 80-150°C and the pressure range 80-130 bar, representing conditions suggested for the water-rock interface on Enceladus. With this new facility, we investigate the hydrothermal processing of triglycine (GGG) peptide and, for the first time, analyse the extracted samples using laser-induced liquid beam ion desorption (LILBID) mass spectrometry, a laboratory analogue for impact ionization mass spectrometry of ice grains in space. We outline an approach to elucidate hydrothermally processed GGG in ice grains ejected from icy moons based on characteristic differences between GGG anion and cation mass spectra. These differences are linked to hydrothermal processing and thus provide a fingerprint of hydrothermal activity on extraterrestrial bodies. These results will serve as important guidelines for biosignatures potentially obtained by a future Enceladus mission and the SUrface Dust Analyzer (SUDA) instrument onboard Europa Clipper. This article is part of the theme issue 'Dust in the Solar System and beyond'.
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The selected ice nanoparticle accelerator, SELINA, was used to prepare beams of single ice particles with positive or negative charge. Positively charged particles were prepared from deionized water and 0.05-0.2 molar solutions of sodium chloride in water, and negatively charged ice particles were generated from water without salt. Depending on the electrospray source configuration, the measured particles vary from 50 to 1000 nm in diameter. The kinetic energy per charge for all particles was set to 200 eV by the collisional equilibration in quadrupoles, which resulted in primary velocities up to 600 m/s for the lowest m/z particles. The electrospray ionization and thus particle formation from SELINA become less efficient with increasing salt concentration, resulting in a lower detected particle frequency and size. Good instrument operation is achievable for concentrations below 0.2 M. After we have verified and characterized positively and negatively charged ice particles, we have combined SELINA with a target and time-of-flight spectrometer for a 'proof-of-principle' post acceleration of 120 nm particles towards hypervelocity (v ~ 3000 m/s) and detection of fragments from the particle impact (SELINA-HIMS). General conditions are discussed for the acceleration of particles between 50 and 1000 nm to velocities well above 3000 m/s with SELINA-HIMS instrument. This article is part of the theme issue 'Dust in the Solar System and beyond'.
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The DESTINY+(Demonstration and Experiment of Space Technology for INterplanetary voYage with Phaethon fLyby and dUst Science) Dust Analyser (DDA) is a state-of-the-art dust telescope for the in situ analysis of cosmic dust particles. As the primary scientific payload of the DESTINY+ mission, it serves the purpose of characterizing the dust environment within the Earth-Moon system, investigating interplanetary and interstellar dust populations at 1 AU from the Sun and studying the dust cloud enveloping the asteroid (3200) Phaethon. DDA features a two-axis pointing platform for increasing the accessible fraction of the sky. The instrument combines a trajectory sensor with an impact ionization time-of-flight mass spectrometer, enabling the correlation of dynamical, physical and compositional properties for individual dust grains. For each dust measurement, a set of nine signals provides the surface charge, particle size, velocity vector, as well as the atomic, molecular and isotopic composition of the dust grain. With its capabilities, DDA is a key asset in advancing our understanding of the cosmic dust populations present along the orbit of DESTINY+. In addition to providing the scientific context, we are presenting an overview of the instrument's design and functionality, showing first laboratory measurements and giving insights into the observation planning. This article is part of a theme issue 'Dust in the Solar System and beyond'.
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Icy moons like Enceladus, and perhaps Europa, emit material sourced from their subsurface oceans into space via plumes of ice grains and gas. Both moons are prime targets for astrobiology investigations. Cassini measurements revealed a large compositional diversity of emitted ice grains with only 1 to 4% of Enceladus's plume ice grains containing organic material in high concentrations. Here, we report experiments simulating mass spectra of ice grains containing one bacterial cell, or fractions thereof, as encountered by advanced instruments on board future space missions to Enceladus or Europa, such as the SUrface Dust Analyzer onboard NASA's upcoming Europa Clipper mission at flyby speeds of 4 to 6 kilometers per second. Mass spectral signals characteristic of the bacteria are shown to be clearly identifiable by future missions, even if an ice grain contains much less than one cell. Our results demonstrate the advantage of analyses of individual ice grains compared to a diluted bulk sample in a heterogeneous plume.
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Medio Ambiente Extraterrestre , Júpiter , Hielo , Exobiología/métodos , Océanos y MaresRESUMEN
The concept of a biosignature is widely used in astrobiology to suggest a link between some observation and a biological cause, given some context. The term itself has been defined and used in several ways in different parts of the scientific community involved in the search for past or present life on Earth and beyond. With the ongoing acceleration in the search for life in distant time and/or deep space, there is a need for clarity and accuracy in the formulation and reporting of claims. Here, we critically review the biosignature concept(s) and the associated nomenclature in light of several problems and ambiguities emphasized by recent works. One worry is that these terms and concepts may imply greater certainty than is usually justified by a rational interpretation of the data. A related worry is that terms such as "biosignature" may be inherently misleading, for example, because the divide between life and non-life-and their observable effects-is fuzzy. Another worry is that different parts of the multidisciplinary community may use non-equivalent or conflicting definitions and conceptions, leading to avoidable confusion. This review leads us to identify a number of pitfalls and to suggest how they can be circumvented. In general, we conclude that astrobiologists should exercise particular caution in deciding whether and how to use the concept of biosignature when thinking and communicating about habitability or life. Concepts and terms should be selected carefully and defined explicitly where appropriate. This would improve clarity and accuracy in the formulation of claims and subsequent technical and public communication about some of the most profound and important questions in science and society. With this objective in mind, we provide a checklist of questions that scientists and other interested parties should ask when assessing any reported detection of a "biosignature" to better understand exactly what is being claimed.
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Aceleración , Planeta Tierra , ExobiologíaRESUMEN
Saturn's moon Enceladus harbours a global1 ice-covered water ocean2,3. The Cassini spacecraft investigated the composition of the ocean by analysis of material ejected into space by the moon's cryovolcanic plume4-9. The analysis of salt-rich ice grains by Cassini's Cosmic Dust Analyzer10 enabled inference of major solutes in the ocean water (Na+, K+, Cl-, HCO3-, CO32-) and its alkaline pH3,11. Phosphorus, the least abundant of the bio-essential elements12-14, has not yet been detected in an ocean beyond Earth. Earlier geochemical modelling studies suggest that phosphate might be scarce in the ocean of Enceladus and other icy ocean worlds15,16. However, more recent modelling of mineral solubilities in Enceladus's ocean indicates that phosphate could be relatively abundant17. Here we present Cassini's Cosmic Dust Analyzer mass spectra of ice grains emitted by Enceladus that show the presence of sodium phosphates. Our observational results, together with laboratory analogue experiments, suggest that phosphorus is readily available in Enceladus's ocean in the form of orthophosphates, with phosphorus concentrations at least 100-fold higher in the moon's plume-forming ocean waters than in Earth's oceans. Furthermore, geochemical experiments and modelling demonstrate that such high phosphate abundances could be achieved in Enceladus and possibly in other icy ocean worlds beyond the primordial CO2 snowline, either at the cold seafloor or in hydrothermal environments with moderate temperatures. In both cases the main driver is probably the higher solubility of calcium phosphate minerals compared with calcium carbonate in moderately alkaline solutions rich in carbonate or bicarbonate ions.
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The reliable identification of biosignatures is key to the search for life elsewhere. On ocean worlds like Enceladus or Europa, this can be achieved by impact ionization mass spectrometers, such as the SUrface Dust Analyzer (SUDA) on board NASA's upcoming Europa Clipper mission. During spacecraft flybys, these instruments can sample ice grains formed from subsurface water and emitted by these moons. Previous laboratory analog experiments have demonstrated that SUDA-type instruments could identify amino acids, fatty acids, and peptides in ice grains and discriminate between their abiotic and biotic origins. Here, we report experiments simulating impact ionization mass spectra of ice grains containing DNA, lipids, and metabolic intermediates extracted from two bacterial cultures: Escherichia coli and Sphingopyxis alaskensis. Salty Enceladan or Europan ocean waters were simulated using matrices with different NaCl concentrations. Characteristic mass spectral signals, such as DNA nucleobases, are clearly identifiable at part-per-million-level concentrations. Mass spectra of all substances exhibit unambiguous biogenic patterns, which in some cases show significant differences between the two bacterial species. Sensitivity to the biosignatures decreases with increasing matrix salinity. The experimental parameters indicate that future impact ionization mass spectrometers will be most sensitive to the investigated biosignatures for ice grain encounter speeds of 4-6 km/s.
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Medio Ambiente Extraterrestre , Hielo , Medio Ambiente Extraterrestre/química , Exobiología , Bacterias , LípidosRESUMEN
Identifying and distinguishing between abiotic and biotic signatures of organic molecules such as amino acids and fatty acids is key to the search for life on extraterrestrial ocean worlds. Impact ionization mass spectrometers can potentially achieve this by sampling water ice grains formed from ocean water and ejected by moons such as Enceladus and Europa, thereby exploring the habitability of their subsurface oceans in spacecraft flybys. Here, we extend previous high-sensitivity laser-based analog experiments of biomolecules in pure water to investigate the mass spectra of amino acids and fatty acids at simulated abiotic and biotic relative abundances. To account for the complex background matrix expected to emerge from a salty Enceladean ocean that has been in extensive chemical exchange with a carbonaceous rocky core, other organic and inorganic constituents are added to the biosignature mixtures. We find that both amino acids and fatty acids produce sodiated molecular peaks in salty solutions. Under the soft ionization conditions expected for low-velocity (2-6 km/s) encounters of an orbiting spacecraft with ice grains, the unfragmented molecular spectral signatures of amino acids and fatty acids accurately reflect the original relative abundances of the parent molecules within the source solution, enabling characteristic abiotic and biotic relative abundance patterns to be identified. No critical interferences with other abiotic organic compounds were observed. Detection limits of the investigated biosignatures under Enceladus-like conditions are salinity dependent (decreasing sensitivity with increasing salinity), at the µM or nM level. The survivability and ionization efficiency of large organic molecules during impact ionization appear to be significantly improved when they are protected by a frozen water matrix. We infer from our experimental results that encounter velocities of 4-6 km/s are most appropriate for impact ionization mass spectrometers to detect and discriminate between abiotic and biotic signatures.
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Aminoácidos/análisis , Exobiología , Ácidos Grasos/análisis , Hielo , Medio Ambiente Extraterrestre , Hielo/análisis , Planetas Menores , Océanos y MaresRESUMEN
Research on the origin of life is highly heterogeneous. After a peculiar historical development, it still includes strongly opposed views which potentially hinder progress. In the 1st Interdisciplinary Origin of Life Meeting, early-career researchers gathered to explore the commonalities between theories and approaches, critical divergence points, and expectations for the future. We find that even though classical approaches and theories-e.g. bottom-up and top-down, RNA world vs. metabolism-first-have been prevalent in origin of life research, they are ceasing to be mutually exclusive and they can and should feed integrating approaches. Here we focus on pressing questions and recent developments that bridge the classical disciplines and approaches, and highlight expectations for future endeavours in origin of life research.
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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.
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Biomarcadores/análisis , Exobiología/métodos , Medio Ambiente Extraterrestre/química , Hielo/análisis , Espectrometría de Masas/métodos , Aminoácidos/análisis , Polvo Cósmico/análisis , Ácidos Grasos/análisis , Límite de Detección , Océanos y Mares , Péptidos/análisis , SaturnoRESUMEN
RATIONALE: Detecting ice grains with impact ionization mass spectrometers in space provides information about the compositions of ice grains and their sources. Depending on the impact speeds of the ice grains onto the metal target of a mass spectrometer, ionization conditions can vary substantially, resulting in changes to the appearance of the resulting mass spectra. METHODS: Here we accurately reproduce mass spectra of water ice grains, recorded with the Cosmic Dust Analyzer (CDA) on board the Cassini spacecraft at typical impact speeds ranging between 4 km/s to 21 km/s, with a laboratory analogue experiment. In this Laser-Induced Liquid Beam Ion Desorption (LILBID) approach, a µm-sized liquid water beam is irradiated with a pulsed infrared laser, desorbing charged analyte and solvent aggregates and isolated ions, which are subsequently analyzed in a time-of-flight (TOF) mass spectrometer. RESULTS: We show that our analogue experiment can reproduce impact ionization mass spectra of ice grains obtained over a wide range of impact speeds, aiding the quantitative analyses of mass spectra from space. CONCLUSIONS: Spectra libraries created with the LILBID experiment will be a vital tool for inferring the composition of ice grains from mass spectra recorded by both past and future impact ionization mass spectrometers (e.g. the SUrface Dust Analyzer (SUDA) onboard NASA's Europa Clipper Mission or detectors on a future Enceladus Mission).
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Saturn's main rings are composed of >95% water ice, and the nature of the remaining few percent has remained unclear. The Cassini spacecraft's traversals between Saturn and its innermost D ring allowed its cosmic dust analyzer (CDA) to collect material released from the main rings and to characterize the ring material infall into Saturn. We report the direct in situ detection of material from Saturn's dense rings by the CDA impact mass spectrometer. Most detected grains are a few tens of nanometers in size and dynamically associated with the previously inferred "ring rain." Silicate and water-ice grains were identified, in proportions that vary with latitude. Silicate grains constitute up to 30% of infalling grains, a higher percentage than the bulk silicate content of the rings.
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Saturn's moon Enceladus harbours a global water ocean 1 , which lies under an ice crust and above a rocky core 2 . Through warm cracks in the crust 3 a cryo-volcanic plume ejects ice grains and vapour into space4-7 that contain materials originating from the ocean8,9. Hydrothermal activity is suspected to occur deep inside the porous core10-12, powered by tidal dissipation 13 . So far, only simple organic compounds with molecular masses mostly below 50 atomic mass units have been observed in plume material6,14,15. Here we report observations of emitted ice grains containing concentrated and complex macromolecular organic material with molecular masses above 200 atomic mass units. The data constrain the macromolecular structure of organics detected in the ice grains and suggest the presence of a thin organic-rich film on top of the oceanic water table, where organic nucleation cores generated by the bursting of bubbles allow the probing of Enceladus' organic inventory in enhanced concentrations.