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S Kempf - One of the best experts on this subject based on the ideXlab platform.

  • ongoing hydrothermal activities within Enceladus
    Nature, 2015
    Co-Authors: Hsiangwen Hsu, M Horanyi, Yasuhito Sekine, Takazo Shibuya, Katsuhiko Suzuki, Frank Postberg, S Kempf, Antal Juhasz, Nicolas Altobelli, Yuka Masaki
    Abstract:

    Analysis of silicon-rich, nanometre-sized dust particles near Saturn shows them to consist of silica, which was initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring; their properties indicate their ongoing formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Hsiang-Wen Hsu et al. have analysed the silicon-rich, nanometre-sized dust stream particles in the Saturnian system using the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. With the help of experiments and modelling, the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on Enceladus and released by sputter erosion in Saturn's E ring. Their properties indicate their formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Detection of sodium-salt-rich ice grains emitted from the plume of the Saturnian moon Enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is, or has been, in contact with rock1,2. Gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3. These findings imply rock–water interactions in regions surrounding the core of Enceladus. The resulting chemical ‘footprints’ are expected to be preserved in the liquid and subsequently transported upwards to the near-surface plume sources, where they eventually would be ejected and could be measured by a spacecraft4. Here we report an analysis of silicon-rich, nanometre-sized dust particles5,6,7,8 (so-called stream particles) that stand out from the water-ice-dominated objects characteristic of Saturn. We interpret these grains as nanometre-sized SiO2 (silica) particles, initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring. The composition and the limited size range (2 to 8 nanometres in radius) of stream particles indicate ongoing high-temperature (>90 °C) hydrothermal reactions associated with global-scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of Enceladus.

  • how the Enceladus dust plume feeds saturn s e ring
    Icarus, 2010
    Co-Authors: S Kempf, U Beckmann, Jurgen Schmidt
    Abstract:

    Abstract Pre-Cassini models of Saturn’s E ring [Horanyi, M., Burns, J., Hamilton, D., 1992. Icarus 97, 248–259; Juhasz, A., Horanyi, M., 2002. J. Geophys. Res. 107, 1–10] failed to reproduce its peculiar vertical structure inferred from Earth-bound observations [de Pater, I., Martin, S.C., Showalter, M.R., 2004. Icarus 172, 446–454]. After the discovery of an active ice-volcanism of Saturn’s icy moon Enceladus the relevance of the directed injection of particles for the vertical ring structure of the E ring was swiftly recognised [Juhasz, A., Horanyi, M., Morfill, G.E., 2007. Geophys. Res. Lett. 34, L09104; Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., Economou, T., Schmidt, J., Spahn, F., Grun, E., 2008. Icarus 193, 420–437]. However, simple models for the delivery of particles from the plume to the ring predict a too small vertical ring thickness and overestimate the amount of the injected dust. Here we report on numerical simulations of grains leaving the plume and populating the dust torus of Enceladus. We run a large number of dynamical simulations including gravity and Lorentz force to investigate the earliest phase of the ring particle life span. The evolution of the electrostatic charge carried by the initially uncharged grains is treated selfconsistently. Freshly ejected plume particles are moving in almost circular orbits because the Enceladus orbital speed exceeds the particles’ ejection speeds by far. Only a small fraction of grains that leave the Hill sphere of Enceladus survive the next encounter with the moon. Thus, the flux and size distribution of the surviving grains, replenishing the ring particle reservoir, differs significantly from the flux and size distribution of the particles freshly ejected from the plume. Our numerical simulations reproduce the vertical ring profile measured by the Cassini Cosmic Dust Analyzer (CDA) [Kempf, S., Beckmann, U., Moragas-Klostermeyer, G., Postberg, F., Srama, R., EconoDmou, T., Smchmidt, J., Spahn, F., Grun, E., 2008. Icarus 193, 420–437]. From our simulations we calculate the deposition rates of plume particles hitting Enceladus’ surface. We find that at a distance of 100 m from a jet a 10 m sized ice boulder should be covered by plume particles in 10 5 – 10 6 years.

  • sodium salts in e ring ice grains from an ocean below the surface of Enceladus
    Nature, 2009
    Co-Authors: F Postberg, Nikolai V Brilliantov, Jurgen Schmidt, S Kempf, A Beinsen, B Abel, Udo Buck, Ralf Srama
    Abstract:

    Images from the Cassini spacecraft showed erupting plumes of water vapour and ice particles on Saturn's moon Enceladus, prompting speculation a subsurface ocean might be acting as a source of liquid water. Two groups this week report evidence relevant to the search for this subsurface ocean. The results, at first sight contradictory, leave the ocean a possibility, though still a hypothetical one. Postberg et al. used the Cassini Cosmic Dust Analyser to determine the chemical composition of ice grains in Saturn's E-ring, which consists largely of material from Enceladus. They find a population of E-ring grains rich in sodium salts, which should be possible only if the plumes originate from liquid water. Schneider et al. used Earth-based spectroscopic telescopes to search for sodium emission in the gas plumes erupting from Enceladus and found none. This is inconsistent with a direct supply from a salty ocean and suggests alternative eruption sources such as a deep ocean, a freshwater reservoir or ice. Or if there is a salty reservoir of water, some process not yet determined must be preventing the sodium from escaping into space. Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole, raising the possibility of a subsurface ocean. Minor organic or siliceous components, identified in many ice grains, could be evidence of interaction between Enceladus' rocky core and liquid water; however it has been unclear whether the water is still present today or if it has frozen. Now, the identification of a population of E-ring grains that are rich in sodium salts suggests that the plumes originate from liquid water. Saturn's moon Enceladus emits plumes of water vapour and ice particles from fractures near its south pole1,2,3,4,5, suggesting the possibility of a subsurface ocean5,6,7. These plume particles are the dominant source of Saturn’s E ring7,8. A previous in situ analysis9 of these particles concluded that the minor organic or siliceous components, identified in many ice grains, could be evidence for interaction between Enceladus’ rocky core and liquid water9,10. It was not clear, however, whether the liquid is still present today or whether it has frozen. Here we report the identification of a population of E-ring grains that are rich in sodium salts (∼0.5–2% by mass), which can arise only if the plumes originate from liquid water. The abundance of various salt components in these particles, as well as the inferred basic pH, exhibit a compelling similarity to the predicted composition of a subsurface Enceladus ocean in contact with its rock core11. The plume vapour is expected to be free of atomic sodium. Thus, the absence of sodium from optical spectra12 is in good agreement with our results. In the E ring the upper limit for spectroscopy12 is insufficiently sensitive to detect the concentrations we found.

  • the e ring in the vicinity of Enceladus ii probing the moon s interior the composition of e ring particles
    Icarus, 2008
    Co-Authors: Frank Postberg, S Kempf, Ralf Srama, Jon K Hillier, S F Green, Neil Mcbride, E Grun
    Abstract:

    The population of Saturn's outermost tenuous E-ring is dominated by tiny water ice particles. Active volcanism on the moon Enceladus, embedded in the E-ring, has since late 2005 been known to be a major source of particles replenishing the ring. Therefore particles in the vicinity of Enceladus may provide crucial information about the dynamical and chemical processes occurring below the moon's icy surface. Here we present a statistical evaluation of more than 2000 impact ionisation mass spectra of Saturn's E-ring particles, with sizes predominantly below 1 μm, detected by the Cosmic Dust Analyser onboard the Cassini spacecraft. We focus on the identification of non-water features in spectra otherwise dominated by water ice signatures. Here we specify the categorisation of two different spectrum types, which probably represent two particle populations. Type I spectra imply pure water ice particles, whereas in Type II spectra organic compounds and/or silicate minerals are identified as impurities within the icy particles. This finding supports the hypothesis of a dynamic interaction of Enceladus' rocky core with liquid water.

  • the e ring in the vicinity of Enceladus i spatial distribution and properties of the ring particles
    Icarus, 2008
    Co-Authors: S Kempf, Jurgen Schmidt, Frank Spahn, Frank Postberg, Ralf Srama, U Beckmann, Georg Moragasklostermeyer, T Economou, E Grun
    Abstract:

    Abstract Saturn's diffuse E ring is the largest ring of the Solar System and extends from about 3.1 R S (Saturn radius R S = 60 , 330 km ) to at least 8 R S encompassing the icy moons Mimas, Enceladus, Tethys, Dione, and Rhea. After Cassini's insertion into her saturnian orbit in July 2004, the spacecraft performed a number of equatorial as well as steep traversals through the E ring inside the orbit of the icy moon Dione. Here, we report about dust impact data we obtained during 2 shallow and 6 steep crossings of the orbit of the dominant ring source—the ice moon Enceladus. Based on impact data of grains exceeding 0.9 μm we conclude that Enceladus feeds a torus populated by grains of at least this size along its orbit. The vertical ring structure at 3.95 R S agrees well with a Gaussian with a full-width–half-maximum (FWHM) of ∼ 4200 km . We show that the FWHM at 3.95 R S is due to three-body interactions of dust grains ejected by Enceladus' recently discovered ice volcanoes with the moon during their first orbit. We find that particles with initial speeds between 225 and 235 m s−1 relative to the moon's surface dominate the vertical distribution of dust. Particles with initial velocities exceeding the moon's escape speed of 207 m s−1 but slower than 225 m s−1 re-collide with Enceladus and do not contribute to the ring particle population. We find the peak number density to range between 16 × 10 −2 m −3 and 21 × 10 −2 m −3 for grains larger 0.9 μm, and 2.1 × 10 −2 m −3 and 7.6 × 10 −2 m −3 for grains larger than 1.6 μm. Our data imply that the densest point is displaced outwards by at least 0.05 R S with respect of the Enceladus orbit. This finding provides direct evidence for plume particles dragged outwards by the ambient plasma. The differential size distribution n ( s d ) d s d ∼ s d − q s d s d for grains > 0.9 μm is described best by a power law with slopes between 4 and 5. We also obtained dust data during ring plane crossings in the vicinity of the orbits of Mimas and Tethys. The vertical distribution of grains > 0.8 μm at Mimas orbit is also well described by Gaussian with a FWHM of ∼ 5400 km and displaced southwards by ∼ 1200 km with respect to the geometrical equator. The vertical distribution of ring particles in the vicinity of Tethys, however, does not match a Gaussian. We use the FWHM values obtained from the vertical crossings to establish a 2-dimensional model for the ring particle distribution which matches our observations during vertical and equatorial traversals through the E ring.

Carolyn C Porco - One of the best experts on this subject based on the ideXlab platform.

  • tidally modulated eruptions on Enceladus cassini iss observations and models
    The Astronomical Journal, 2014
    Co-Authors: F Nimmo, Carolyn C Porco, Colin Mitchell
    Abstract:

    We use images acquired by the Cassini Imaging Science Subsystem (ISS) to investigate the temporal variation of the brightness and height of the south polar plume of Enceladus. The plume’s brightness peaks around the moon’s apoapse, but with no systematic variation in scale height with either plume brightness or Enceladus’ orbital position. We compare our results, both alone and supplemented with Cassini near-infrared observations, with predictions obtained from models in which tidal stresses are the principal control of the eruptive behavior. There are three main ways of explaining the observations: (1) the activity is controlled by right-lateral strike slip motion; (2) the activity is driven by eccentricity tides with an apparent time delay of about 5 hr; (3) the activity is driven by eccentricity tides plus a 1:1 physical libration with an amplitude of about 0. ◦ 8 (3.5 km). The second hypothesis might imply either a delayed eruptive response, or a dissipative, viscoelastic interior. The third hypothesis requires a libration amplitude an order of magnitude larger than predicted for a solid Enceladus. While we cannot currently exclude any of these hypotheses, the third, which is plausible for an Enceladus with a subsurface ocean, is testable by using repeat imaging of the moon’s surface. A dissipative interior suggests that a regional background heat source should be detectable. The lack of a systematic variation in plume scale height, despite the large variations in plume brightness, is plausibly the result of supersonic flow; the details of the eruption process are yet to be understood.

  • the possible origin and persistence of life on Enceladus and detection of biomarkers in the plume
    Astrobiology, 2008
    Co-Authors: Christopher P Mckay, Carolyn C Porco, Travis S Altheide, Wanda L Davis, Timothy A Kral
    Abstract:

    The jets of icy particles and water vapor issuing from the south pole of Enceladus are evidence for activity driven by some geophysical energy source. The vapor has also been shown to contain simple organic compounds, and the south polar terrain is bathed in excess heat coming from below. The source of the ice and vapor, and the mechanisms that accelerate the material into space, remain obscure. However, it is possible that a liquid water environment exists beneath the south polar cap, which may be conducive to life. Several theories for the origin of life on Earth would apply to Enceladus. These are (1) origin in an organic-rich mixture, (2) origin in the redox gradient of a submarine vent, and (3) panspermia. There are three microbial ecosystems on Earth that do not rely on sunlight, oxygen, or organics produced at the surface and, thus, provide analogues for possible ecologies on Enceladus. Two of these ecosystems are found deep in volcanic rock, and the primary productivity is based on the consumption by methanogens of hydrogen produced by rock reactions with water. The third ecosystem is found deep below the surface in South Africa and is based on sulfur-reducing bacteria consuming hydrogen and sulfate, both of which are ultimately produced by radioactive decay. Methane has been detected in the plume of Enceladus and may be biological in origin. An indicator of biological origin may be the ratio of non-methane hydrocarbons to methane, which is very low (0.001) for biological sources but is higher (0.1-0.01) for nonbiological sources. Thus, Cassini's instruments may detect plausible evidence for life by analysis of hydrocarbons in the plume during close encounters.

  • association of the jets of Enceladus with the warmest regions on its south polar fractures
    Nature, 2007
    Co-Authors: Joseph N Spitale, Carolyn C Porco
    Abstract:

    The Cassini flyby of 14 July 2005 revealed plumes of jets of water vapour and ice emanating from near the south pole of Saturn's icy moon Enceladus. This region is anomalously warm, with the highest temperatures associated with four 'tiger stripe' surface fractures on the moon's surface, colourfully named Alexandria, Cairo, Baghdad and Damascus. Joseph Spitale and Carolyn Porco have now applied triangulation techniques to Cassini images in order to obtain accurate bearings on the sources of the most prominent jets, and they find that they emanate from the tiger stripes, with the strongest sources situated on Baghdad and Damascus. Jets of material have been seen emanating from the south-polar terrain of Saturn's satellite Enceladus. Observations have shown that region is anomalously warm, with the hottest measured temperatures coinciding with four 'tiger stripe' fractures. Cassini images are used to triangulate the source locations for the most prominent jets, and find that the jets emanate from the four tiger stripes. Jets of material have been seen emanating from the south-polar terrain of Saturn’s satellite Enceladus1. Observations have shown that this region is anomalously warm2, with the hottest measured temperatures coinciding with the four ‘tiger stripe’ fractures, named Alexandria, Cairo, Baghdad and Damascus, that straddle the region1,2. Here we use Cassini images taken from a variety of viewing directions over two years to triangulate the source locations for the most prominent jets, and compare these with the infrared hotspot locations and the predictions from a recent model of tidally induced shear heating within the fractures3. We find that the jets emanate from the four tiger stripes, with the strongest sources on Baghdad and Damascus. All the jets from each fracture seem to lie in the same nearly vertical plane. There is a strong spatial coincidence between our geographical sources and the locations of increased temperature revealed by the infrared experiment. Comparison with the shear heating model shows broad agreement; the exception is the prediction that Baghdad is the least active lineament, whereas we find it to be the most active. We predict that several new hotspots remain to be discovered by future thermal observations.

  • shapes of the saturnian icy satellites and their significance
    Icarus, 2007
    Co-Authors: P.c. Thomas, Joseph A Burns, T Denk, P Helfenstein, E P Turtle, A S Mcewen, Carolyn C Porco, S W Squyres, J Veverka, Bernd Giese
    Abstract:

    The sizes and shapes of six icy saturnian satellites have been measured from Cassini Imaging Science Subsystem (ISS) data, employing limb coordinates and stereogrammetric control points. Mimas, Enceladus, Tethys, Dione and Rhea are well described by triaxial ellipsoids; Iapetus is best represented by an oblate spheroid. All satellites appear to have approached relaxed, equilibrium shapes at some point in their evolution, but all support at least 300 m of global-wavelength topography. The shape of Enceladus is most consistent with a homogeneous interior. If Enceladus is differentiated, its shape and apparent relaxation require either lateral inhomogeneities in an icy mantle and/or an irregularly shaped core. Iapetus supports a fossil bulge of over 30 km, and provides a benchmark for impact modification of shapes after global relaxation. Satellites such as Mimas that have smoother limbs than Iapetus, and are expected to have higher impact rates, must have relaxed after the shape of Iapetus was frozen.

R E Johnson - One of the best experts on this subject based on the ideXlab platform.

  • seasonal variations in saturn s plasma between the main rings and Enceladus
    Journal of Geophysical Research, 2012
    Co-Authors: M K Elrod, R J Wilson, W L Tseng, R E Johnson
    Abstract:

    [1] With the discovery by the Cassini spacecraft of an oxygen atmosphere over Saturn's main rings, and a strong source of water products from the plumes of Saturn's moon Enceladus, our picture of the physics of Saturn's magnetosphere from the main rings to inside the orbit of Enceladus has changed dramatically. This region contains oxygen ions from the ring atmosphere and water-group ions from the Enceladus torus. The purpose of this study is to examine ion densities, temperatures, and composition from several equatorial periapsis passes from 2004 to 2010 for the region from 2.4 to 3.5 Saturn radii (∼60,300 km) in addition to Voyager 2 in order to separate contributions from Saturn's ring atmosphere from the water products in the Enceladus torus and to describe the temporal variations in the plasma. Because of the high background due to so-called penetrating radiation in this region, only six orbits are used in this study. Our analysis indicates that large variations in ion density, temperature, and composition occurred between the Voyager 2 flyby, 2004, and 2010. Although the Enceladus plumes may be variable, we propose that the large change in the ion density from 2004 to equinox near 2010 is due to the seasonal variation in the ring atmosphere. Our interpretation of the plasma data is supported by a simple photochemical model, combining the water products from Enceladus and the seasonal variations in the ring atmosphere.

  • collisional spreading of Enceladus neutral cloud
    Icarus, 2010
    Co-Authors: Timothy A Cassidy, R E Johnson
    Abstract:

    We describe a direct simulation Monte Carlo (DSMC) model of Enceladus’ neutral cloud and compare its results to observations of OH and O orbiting Saturn. The OH and O are observed far from Enceladus (at 3.95 RS), as far out as 25 RS for O. Previous DSMC models attributed this breadth primarily to ion/neutral scattering (including charge exchange) and molecular dissociation. However, the newly reported O observations and a reinterpretation of the OH observations (Melin, H., Shemansky, D.E., Liu, X. [2009] Planet. Space Sci., 57, 1743–1753, PS&S) showed that the cloud is broader than previously thought. We conclude that the addition of neutral/neutral scattering (Farmer, A.J. [2009] Icarus, 202, 280–286), which was underestimated by previous models, brings the model results in line with the new observations. Neutral/neutral collisions primarily happen in the densest part of the cloud, near Enceladus’ orbit, but contribute to the spreading by pumping up orbital eccentricity. Based on the cloud model presented here Enceladus maybe the ultimate source of oxygen for the upper atmospheres of Titan and Saturn. We also predict that large quantities of OH, O and H2O bombard Saturn’s icy satellites.

  • cassini detection of Enceladus cold water group plume ionosphere
    Geophysical Research Letters, 2009
    Co-Authors: R L Tokar, R E Johnson, M F Thomsen, R J Wilson, D T Young, F J Crary, A J Coates, G H Jones, C S Paty
    Abstract:

    This study reports direct detection by the Cassini plasma spectrometer of freshly-produced water-group ions (O{sup +}, OH{sup +}, H{sub 2}O{sup +}, H{sub 3}O{sup +}) and heavier water dimer ions (H{sub x}O{sub 2}{sup +}) very close to Enceladus and where the plasma begins to emerge from the Enceladus plume The data wcre obtained during two close (52 and 25 km) flybys of Enceladus in 2008, and are similar to ion data in cometary comas. The ions are observed in detectors looking in the Cassini ram direction at energies consistent with the Cassini speed, indicating a nearly stagnant plasma flow in the plume. North of Enceladus the plasma slowing commences about 4 to 6 Enceladus radii away, while south of Enccladus signatures ofthe interaction are detected as far as 22 Enceladus radii away.

  • the Enceladus and oh tori at saturn
    The Astrophysical Journal, 2006
    Co-Authors: R E Johnson, H T Smith, O J Tucker, Mengyao Liu, M H Burger, E C Sittler, R L Tokar
    Abstract:

    The remarkable observation that Enceladus, a small icy satellite of Saturn, is actively venting has led to the suggestion that ejected water molecules are the source of the toroidal atmosphere observed at Saturn for over a decade using the Hubble Space Telescope (HST). Here we show that the venting leads directly to a new feature, a narrow Enceladus neutral torus. The larger torus, observed using HST, is populated by charge exchange, the process that limits the lifetime of the neutrals in the Enceladus torus.

  • the interaction of the atmosphere of Enceladus with saturn s plasma
    Science, 2006
    Co-Authors: R L Tokar, R E Johnson, M F Thomsen, D T Young, F J Crary, T W Hill, Duane H Pontius, W S Kurth, D B Reisenfeld, A J Coates
    Abstract:

    During the 14 July 2005 encounter of Cassini with Enceladus, the Cassini Plasma Spectrometer measured strong deflections in the corotating ion flow, commencing at least 27 Enceladus radii (27 x 252.1 kilometers) from Enceladus. The Cassini Radio and Plasma Wave Science instrument inferred little plasma density increase near Enceladus. These data are consistent with ion formation via charge exchange and pickup by Saturn's magnetic field. The charge exchange occurs between neutrals in the Enceladus atmosphere and corotating ions in Saturn's inner magnetosphere. Pickup ions are observed near Enceladus, and a total mass loading rate of about 100 kilograms per second (3 x 10(27) H(2)O molecules per second) is inferred.

B L Fleshman - One of the best experts on this subject based on the ideXlab platform.

  • modeling the Enceladus plume plasma interaction
    Geophysical Research Letters, 2010
    Co-Authors: B L Fleshman, P A Delamere, F Bagenal
    Abstract:

    [1] We investigate the chemical interaction between Saturn's corotating plasma and Enceladus' volcanic plumes. We evolve a parcel of ambient plasma as it passes through a prescribed H2O plume using a physical chemistry model adapted for water-group reactions. The flow field is assumed to be that of a plasma around an electrically-conducting obstacle centered on Enceladus and aligned with Saturn's magnetic field, consistent with Cassini magnetometer data. We explore the effects on the physical chemistry due to: (1) a small population of hot electrons, (2) a plasma flow decelerated in response to the pickup of fresh ions, and (3) the source rate of neutral H2O. The model confirms that charge exchange dominates the local chemistry and that H3O+ dominates the water-group composition downstream of the Enceladus plumes. We also find that the amount of fresh pickup ions depends heavily on both the neutral source strength and on the presence of a persistent population of hot electrons.

  • modeling the Enceladus plume plasma interaction
    arXiv: Earth and Planetary Astrophysics, 2010
    Co-Authors: B L Fleshman, P A Delamere, F Bagenal
    Abstract:

    We investigate the chemical interaction between Saturn's corotating plasma and Enceladus' volcanic plumes. We evolve plasma as it passes through a prescribed H2O plume using a physical chemistry model adapted for water-group reactions. The flow field is assumed to be that of a plasma around an electrically-conducting obstacle centered on Enceladus and aligned with Saturn's magnetic field, consistent with Cassini magnetometer data. We explore the effects on the physical chemistry due to: (1) a small population of hot electrons; (2) a plasma flow decelerated in response to the pickup of fresh ions; (3) the source rate of neutral H2O. The model confirms that charge exchange dominates the local chemistry and that H3O+ dominates the water-group composition downstream of the Enceladus plumes. We also find that the amount of fresh pickup ions depends heavily on both the neutral source strength and on the presence of a persistent population of hot electrons.

Hsiangwen Hsu - One of the best experts on this subject based on the ideXlab platform.

  • Enceladus and Titan: Emerging Worlds of the Solar System (ESA Voyage 2050 White Paper)
    2019
    Co-Authors: Ali Sulaiman, Candice Hansen, Nicholas Achilleos, Sushil Atreya, Cesar Bertucci, Andrew Coates, Michele Dougherty, Lina Hadid, Mika Holmberg, Hsiangwen Hsu
    Abstract:

    This white paper briefly describes outstanding questions pertaining to Titan and Enceladus - legacies of the successful Cassini-Huygens mission. We make the case that such questions are not merely specific to these two mysterious systems but have much broader and deeper implications for humakind’s outstanding questions at large of habitability in the Solar System. For these reasons, we recommend the acknowledgement of Titan and Enceladus as priorities for ESA’s Voayage 2050 programme and to combine efforts, in science and technology, with international agencies to launch a dedicated mission to either or both tagets, much like ESA’s key involvement in some of the most successful planetary missions like Cassini-Huygens.

  • high temperature water rock interactions and hydrothermal environments in the chondrite like core of Enceladus
    Nature Communications, 2015
    Co-Authors: Yasuhito Sekine, Takazo Shibuya, F Postberg, Hsiangwen Hsu, Katsuhiko Suzuki, Yuka Masaki, Tatsu Kuwatani, Megumi Mori, Peng K Hong
    Abstract:

    It has been suggested that Saturn's moon Enceladus possesses a subsurface ocean. The recent discovery of silica nanoparticles derived from Enceladus shows the presence of ongoing hydrothermal reactions in the interior. Here, we report results from detailed laboratory experiments to constrain the reaction conditions. To sustain the formation of silica nanoparticles, the composition of Enceladus' core needs to be similar to that of carbonaceous chondrites. We show that the presence of hydrothermal reactions would be consistent with NH3- and CO2-rich plume compositions. We suggest that high reaction temperatures (>50 °C) are required to form silica nanoparticles whether Enceladus' ocean is chemically open or closed to the icy crust. Such high temperatures imply either that Enceladus formed shortly after the formation of the solar system or that the current activity was triggered by a recent heating event. Under the required conditions, hydrogen production would proceed efficiently, which could provide chemical energy for chemoautotrophic life.

  • ongoing hydrothermal activities within Enceladus
    Nature, 2015
    Co-Authors: Hsiangwen Hsu, M Horanyi, Yasuhito Sekine, Takazo Shibuya, Katsuhiko Suzuki, Frank Postberg, S Kempf, Antal Juhasz, Nicolas Altobelli, Yuka Masaki
    Abstract:

    Analysis of silicon-rich, nanometre-sized dust particles near Saturn shows them to consist of silica, which was initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring; their properties indicate their ongoing formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Hsiang-Wen Hsu et al. have analysed the silicon-rich, nanometre-sized dust stream particles in the Saturnian system using the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. With the help of experiments and modelling, the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on Enceladus and released by sputter erosion in Saturn's E ring. Their properties indicate their formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Detection of sodium-salt-rich ice grains emitted from the plume of the Saturnian moon Enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is, or has been, in contact with rock1,2. Gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick3. These findings imply rock–water interactions in regions surrounding the core of Enceladus. The resulting chemical ‘footprints’ are expected to be preserved in the liquid and subsequently transported upwards to the near-surface plume sources, where they eventually would be ejected and could be measured by a spacecraft4. Here we report an analysis of silicon-rich, nanometre-sized dust particles5,6,7,8 (so-called stream particles) that stand out from the water-ice-dominated objects characteristic of Saturn. We interpret these grains as nanometre-sized SiO2 (silica) particles, initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring. The composition and the limited size range (2 to 8 nanometres in radius) of stream particles indicate ongoing high-temperature (>90 °C) hydrothermal reactions associated with global-scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of Enceladus.