Complex craters with diameters (D) >= 40 km on Callisto and Ganymede are shallower than would be expected from simply extrapolating the depth-diameter trend from smaller (D = 80 km) younger than 200 Myrs, which would retain greater depths, should be relatively rare. If we instead assume that the craters formed at their observed depths, as proposed by previous impact modeling, they quickly become much shallower than observed. We find excellent agreement between observed crater depths on Ganymede and our simulated crater depths by assuming a pure-water ice composition and a diurnally averaged surface temperature of 120 K, but require either larger-grained or dirty ice with a modestly higher viscosity to match observations at Callisto, where the surface temperature is warmer (130 K). We favor the latter explanation because it is consistent with the existence of a dusty lag on Callisto's surface and the absence of a similar lag on Ganymede. Our results predict that, for a given crater diameter, post-relaxation crater depth should increase with increasing latitude, a hypothesis best tested on Callisto, whose relatively quiescent geologic history best preserves the signature of viscous relaxation under radiogenic heating.
The presence of a subsurface ocean on Ganymede moon, the largest and the only moon of solar system that has global magnetic field, marks the existence possibility of sustainable life ecosystems. The phases of this mission involve to launch spacecraft from Earth or the Moon to be landed on the Ganymede moon, using satellite constellation about Ganymede moon, to drill the icy crust of Ganymede moon, reaching the subsurface ocean, and placing submarines or submersibles in the subsurface ocean. The process involves obtaining a sample, analyzing the sample, performing documentation, and reporting the Data to DSN. In this research study, the approach to modeling space systems aims to achieve a mission probability of success of 99% and better, as the author's plans & approach are depicted in Figure.1. The context diagram of this research project encircles active, passive, and paying external stakeholders, with detailed specifications provided in a hierarchy diagram for a probe exploration mission on Ganymede, one of Jupiter's moons. The Pugh diagrams was used to evaluate drilling methods for the Ganymede mission. Quality Function Deployment (QFD) at Level-3 aligned stakeholder needs with engineering design, ensuring mission objectives were met. A Functional Flow Block Diagram (FFBD) illustrated mission workflows, while a risk matrix identified and mitigated potential mission risks.
Sodium chloride is expected to be found on many of the surfaces of icy moons like Europa and Ganymede. However, spectral identification remains elusive as the known NaCl-bearing phases cannot match current observations, which require higher number of water of hydration. Working at relevant conditions for icy worlds, we report the characterization of three hyperhydrated sodium chloride (SC) hydrates, and refined two crystal structures [2NaCl center dot 17H(2)O (SC8.5); NaCl center dot 13H(2)O (SC13)]. We found that the dissociation of Na+ and Cl- ions within these crystal lattices allows for the high incorporation of water molecules and thus explain their hyperhydration. This finding suggests that a great diversity of hyperhydrated crystalline phases of common salts might be found at similar conditions. Thermodynamic constraints indicate that SC8.5 is stable at room pressure below 235 K, and it could be the most abundant NaCl hydrate on icy moon surfaces like Europa, Titan, Ganymede, Callisto, Enceladus, or Ceres. The finding of these hyperhydrated structures represents a major update to the H2O-NaCl phase diagram. These hyperhydrated structures provide an explanation for the mismatch between the remote observations of the surface of Europa and Ganymede and previously available data on NaCl solids. It also underlines the urgent need for mineralogical exploration and spectral data on hyperhydrates at relevant conditions to help future icy world exploration by space missions.
On the basis of results from exhaustive first-principles simulations, we report a thorough description of the recently identified high pressure phase of the CO2 hydrate, and provide an estimation of the transition pressure from the sI low pressure phase to the C-0 high pressure (HP) phase around 0.6 GPa. The vibrational properties calculated here for the first time might be useful to detect this HP structure in extraterrestrial environments, such as the Jupiter ice moons. Interestingly, we also find that CO2 gas molecules are quasi-free to diffuse along the helical channels of the structure, thus allowing the interchange of volatiles across a solid icy barrier. Taking into account its density and comparing it with other substances, we can estimate the naturally occurring zone of this CO2@H2O HP phase within a giant ice moon such as Ganymede. Other potential planetary implications that all of the found properties of this hydrate might have are also discussed.
Ganymede's surface is subject to constant bombardment by Jovian magnetospheric and Ganymede's ionospheric ions. These populations sputter the surface and contribute to the replenishment of the moon's exosphere. Thus far, estimates for sputtering on the moon's surface have included only the contribution from Jovian ions. In this work, we have used our recent model of Ganymede's ionosphere Carnielli et al., 2019 to evaluate the contribution of ionospheric ions for the first time. In addition, we have made new estimates for the contribution from Jovian ions, including both thermal and energetic components. For Jovian ions, we find a total sputtering rate of 2.2 x 10(27) s(-1), typically an order of magnitude higher compared to previous estimates. For ionospheric ions, produced through photo- and electron-impact ionization, we find values in the range 2.7 x 10(26)-5.2 x 10(27) s(-1) when the moon is located above the Jovian plasma sheet. Hence, Ganymede's ionospheric ions provide a contribution of at least 10% to the sputtering rate, and under certain conditions they dominate the process. This finding indicates that the ionospheric population is an important source to consider in the context of exospheric models.
The inner structure of icy moons comprises ices, liquid water, a silicate rocky core and sometimes an inner metallic core depending on thermal evolution and differentiation. Mineralogy and density models for the silicate part of the icy satellites cores were assessed assuming a carbonaceous chondritic (CI) bulk composition and using a free-energy minimization code and experiments. Densities of other components, solid and liquid sulfides, carbonaceous matter, were evaluated from available equations of state. Model densities for silicates are larger than assessed from magnesian terrestrial minerals, by 200 to 600 kg.m(-3) for the hydrated silicates, and 300 to 500 kg.m(-3) for the dry silicates, due to the high iron bulk concentration in CI. The stability of Na-phlogopite in the silicate fraction up to 1300 K favors the trapping of most K-40 in the rocky/carbonaceous cores with important consequences for modeling of the thermal evolution of icy satellites. We find that CI density models of icy satellite cores taking into account only the silicate and metal/sulfide fraction cannot account for the observed densities and reduced moment of inertia of Titan and Ganymede without adding a lower density component. We propose that this low-density component is carbonaceous matter derived from insoluble organic matter, in proportion of similar to 30-40% in volume and 15-20% in mass. This proportion is compatible with contributions from CI and comets, making these primitive bodies including their carbonaceous matter component likely precursors of icy moons, and potentially of most of the objects formed behind the snow line of the solar system. (C) 2019 Elsevier B.V. All rights reserved.
Ozone is known to be present within the surface ice of Jupiter's moon Ganymede as well as Saturn's moons Dione and Rhea. Given the ubiquity of solar photons incident on these water-ice-dominated surfaces, experiments were conducted to better understand the photochemistry of ozone-water ice mixtures. Samples were deposited as thin films in a vacuum chamber under temperature and pressure conditions relevant to satellites in the outer solar system. Chemical changes in the ices were monitored with infrared spectroscopy as they were exposed to ultraviolet light at 116.5/123.6, 147, and 254 nm emitted from Kr, Xe, and Hg resonant lamps, respectively. In all instances, hydrogen peroxide formed after ultraviolet irradiation, while the amount of ozone present decreased. Of the wavelengths tested, irradiation at 254 rim induced the most rapid change both in terms of irradiation time and number of incident photons. This work emphasizes the importance of wavelengths longer than the vacuum ultraviolet in the chemical evolution of ozone on Ganymede, Dione, and Rhea.
Ganymede, the largest moon in the solar system, has a fully differentiated interior with a layer of high-pressure (HP) ice between its deep ocean and silicate mantle. In this paper, we study the dynamics of this layer using a numerical model of two-phase ice-water mixture in two-dimensional Cartesian geometry. While focusing on the generation of water at the silicate/HP ice interface and its upward migration towards the ocean, we investigate the effect of bottom heat flux, the layer thickness, and the HP ice viscosity and permeability. Our results suggest that melt can be generated at the silicate/HP ice interface for small layer thickness (less than or similar to 200 km) and high values of heat flux (greater than or similar to 20 mW m(-2)) and viscosity (greater than or similar to 10(15) Pa s). Once generated, the water is transported through the layer by the upwelling plumes. Depending on the vigor of convection, it stays liquid or it may freeze before melting again as the plume reaches the temperate (partially molten) layer at the boundary with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the permeability of the HP ice. This process constitutes a means of transporting volatiles and salts that might have dissolved into the melt present at the silicate/HP ice interface. As the moon cools down, the HP ice layer becomes less permeable because the heat flux from the silicates decreases and the HP ice layer thickens. (C)2017 Elsevier Inc. All rights reserved.
We describe an interferometric reflectometer method for passive detection of subsurface oceans and liquid water in jovian icy moons using Jupiter's decametric radio emission (DAM). The DAM flux density exceeds 3000 times the galactic background in the neighborhood of the jovian icy moons, providing a signal that could be used for passive radio sounding. An instrument located between the icy moon and Jupiter could sample the DAM emission along with its echoes reflected in the ice layer of the target moon. Cross-correlating the direct emission with the echoes would provide a measurement of the ice shell thickness along with its dielectric properties. The interferometric reflectometer provides a simple solution to sub-jovian radio sounding of ice shells that is complementary to ice penetrating radar measurements better suited to measurements in the anti-jovian hemisphere that shadows Jupiter's strong decametric emission. The passive nature of this technique also serves as risk reduction in case of radar transmitter failure. The interferometric reflectometer could operate with electrically short antennas, thus extending ice depth measurements to lower frequencies, and potentially providing a deeper view into the ice shells of jovian moons. (C) 2014 Elsevier Inc. All rights reserved.
The H2O and O-2 exospheres of Jupiter's moon Ganymede are simulated through the application of a 3D Monte Carlo modeling technique that takes into consideration the combined effect on the exosphere generation of the main surface release processes (i.e. sputtering, sublimation and radiolysis) and the surface precipitation of the energetic ions of Jupiter's magnetosphere. In order to model the magnetospheric ion precipitation to Ganymede's surface, we used as an input the electric and magnetic fields from the global MHD model of Ganymede's magnetosphere (Jia, X., Walker, R.J., Kivelson, M.G., Khurana, K.K., Linker, J.A. [2009]. J. Geophys. Res. 114, A09209). The exospheric model described in this paper is based on EGEON, a single-particle Monte Carlo model already applied for a Galilean satellite (Plainaki, C., Milillo, A., Mura, A., Orsini, S., Cassidy, T. [2010]. Icarus 210, 385-395; Plainaki, C., Milillo, A., Mura, A., Orsini, S., Massetti, S., Cassidy, T. [2012]. Icarus 218 (2), 956-966; Plainaki, C., Milillo, A., Mura, A., Orsini, S., Saur [2013]. Planet. Space Sci. 88,42-52); nevertheless, significant modifications have been implemented in the current work in order to include the effect on the exosphere generation of the ion precipitation geometry determined strongly by Ganymede's intrinsic magnetic field (Kivelson, M.G. et al. [1996]. Nature 384, 537-541). The current simulation refers to a specific configuration between Jupiter, Ganymede and the Sun in which the Galilean moon is located close to the center of Jupiter's Plasma Sheet UPS) with its leading hemisphere illuminated. Our results are summarized as follows: (a) at small altitudes above the moon's subsolar point the main contribution to the neutral environment comes from sublimated H2O; (b) plasma precipitation occurs in a region related to the open-closed magnetic field lines boundary and its extent depends on the assumption used to mimic the plasma mirroring in Jupiter's magnetosphere; (c) the spatial distribution of the directly sputtered-H2O molecules exhibits a close correspondence with the plasma precipitation region and extends at high altitudes, being, therefore, well differentiated from the sublimated water; (d) the O-2 exosphere comprises two different regions: the first one is an homogeneous, relatively dense, close to the surface thermal-O-2 region (extending to some 100s of km above the surface) whereas the second one is less homogeneous and consists of more energetic O-2 molecules sputtered directly from the surface after water-dissociation by ions has taken place; the spatial distribution of the energetic surface-released O-2 molecules depends both on the impacting plasma properties and the moon's surface temperature distribution (that determine the actual efficiency of the radiolysis process). (C) 2014 Elsevier Inc. All rights reserved.