Jupiter Icy Moons Research Articles

Ray Tracing for Jupiter's Icy Moon Ionospheric Occultation of Jovian Auroral Radio Sources

AbstractThe ionospheres of Jupiter's icy moons have been observed by in situ plasma measurements and radio science. However, their spatial structures have not yet been fully characterized. To address this, we developed a new ray tracing method for modeling the radio occultation of the ionospheres using Jovian auroral radio sources. Applying our method to Jovian auroral radio observations with the Galileo spacecraft, we derived the electron density of the ionosphere of Ganymede and Callisto. For Ganymede's ionosphere, we found that the maximum electron density on the surface was 76.5–288.5 cm−3 in the open magnetic field line regions and 5.0–20.5 cm−3 in the closed magnetic field line region during the Galileo Ganymede 01 flyby. The difference in the electron density distribution was correlated with the accessibility of Jovian magnetospheric plasma to the atmosphere and surface of the moons. These results indicated that electron‐impact ionization of the Ganymede exosphere and sputtering of the surface water ice were effective for the producing Ganymede's ionosphere. For Callisto's ionosphere, we found that the densities were approximately 350 and 12.5 cm−3 on the night side hemisphere during Callisto 09 and 30 flybys, respectively. These results combined with previous observations indicated that atmospheric production through sublimation controlled the ionospheric density of Callisto. This method is also applicable to upcoming Jovian radio observation data from the Jupiter Icy Moon Explorer, JUICE.

Structural and spectroscopic study of the kieserite-type (Mg,Mn)SO4·H2O solid solution at ambient and low temperatures relevant to Mars and the icy moons of Jupiter and Saturn

The presence and importance of sulfates in our solar system have become common knowledge among the dedicated scientific community, as well as their crucial role in governing the water budget of planets such as Mars. The formation of subsurface oceans and cryovolcanism on icy moons of Jupiter and Saturn owe their existence to melting equilibria influenced by sulfate hydrates in the deeper parts of these celestial bodies. In such a setting, it cannot be ruled out that lower-hydrated sulfates including kieserite, MgSO4·H2O, are also present, given their stability under geologic pressures relevant even down to the lower mantle of the icy satellites. With regard to the composition of the water-soluble fraction in C1 and C2 chondritic meteorites presumed to correspond to that of the rocky cores of the Jovian moons, local kieserite may contain significant amounts of Mn in addition to Ni (and also some Fe). Minor Mn contents are probable even in kieserite occurring on the surface of Mars. Substantial lattice parameter changes and spectral band shifts between kieserite and its isostructural Mn-analogue szmikite, MnSO4·H2O, are well known, nevertheless neither the existence of a potential MgMn solid solution series nor its crystal chemical and spectroscopic behavior has yet been investigated.This work provides the first evidence for such a continuous solid solution, describes its structural properties, and gives a detailed insight into the position changes of prominent bands in FTIR- and Raman spectra of synthetic samples, as the Mn/Mg ratio increases, with the measurement having been performed both at ambient and low temperatures relevant for Mars and the icy satellites. It reveals that contents of Mn do not cause any significant shift in the H2O stretching vibrational bands, yet influence the position of sulfate-related vibrations much in the same way as the incorporation of other relevant transition metal cations, such as Ni. The contrasting behavior of the ν3 and ν1 stretching vibrations of the H2O molecule in case of Mn- (no shift) and Ni-incorporation (significant shift to lower wavenumber) along with their comparable influence on the position of sulfate bands allow to deduce the chemical composition of kieserite in a ternary Mg–Mn–Ni system based on spectroscopic remote sensing or in situ data from celestial bodies. The assessment of chemical composition from vibrational spectra is facilitated by the observed Vegard-type behavior, where lattice parameters as well as the spectral band positions change along linear trends with increasing substitution of Mg, regardless if by Mn, Fe, or Ni. The observed shift of mainly the H2O stretching vibrations to lower wavenumber values as temperature decreases (in contrast to the bands related to the sulfate group) match thermal behavior observed in other binary solid solutions of sulfate monohydrate phases isostructural with kieserite.

An Ecotheology for Human Settlement of the Outer Planets: Roles for Religion Beyond the Warmth of the Sun

ABSTRACT Settlement of the Outer Planets of the Solar System will take humans far away from the Sun, its warmth, and the light on which humans depend. Most settlements will be small mining enclaves or research stations until well into the future. Lengthy travel times will satisfy the human needs for hope, patience, acceptance, self-study, and contemplation of God's role in the universe. The authors explore the potential roles of theology and religion in Deep Space, the Asteroids, and the icy moons of Jupiter and Saturn where life might be found in the liquid oceans under ice that is kilometers deep.

Topographic response to ocean heat flux anomaly on the icy moons of Jupiter and Saturn

Recent studies of ocean dynamics suggest that the long-wavelength topography of some icy moons may reflect the phase transitions (melting/freezing) at the interface between the ice shell and the water ocean. Despite the obvious importance of phase changes in the evolution of icy moons, very little is known about how these processes influence their shape, gravity and near-surface stress. Here we address this issue by performing a series of numerical experiments in which we explore the thermo-mechanical response of an ice layer to heat flux variations imposed at the bottom (phase) boundary. We assume that the heat flux from the ocean consists of two components: the heat flux originating in the deep ocean and associated with the global ocean circulation, and the heat flux due to the flow of water generated by variations in the melting temperature along the deformed ice–water interface. The effect of salinity on the heat flux from the ocean is neglected. We demonstrate that the mass exchange between the ocean and the ice layer is a natural consequence of the ice–water phase transition and it occurs in both convection and conduction modes, regardless of whether the system is in equilibrium or not. The magnitude of the heat-flux induced topography strongly depends on the viscosity of ice and the flow of water controlled by the melting temperature. When heat transfer in the ice shell occurs by convection, the surface topography is dominated by small-scale convective features varying in time and its large-scale component does not exceed 10 m. When the viscosity of the ice shell is high (≳1016 Pas) and the heat is transferred by conduction, the topography is negatively correlated with the heat flux from the ocean and its amplitude increases with increasing viscosity. Topographic amplitudes comparable to those observed on Titan, Enceladus and Dione are obtained only if the water flow associated with lateral variations in the melting temperature is neglected. This suggests that this flow may be too weak to reduce the variations in ice shell thickness and the motion of water along the phase boundary is more likely to be controlled by other factors, such as variations in salinity and the presence of non-ice material. In addition, we show that the standard formulation of Airy isostasy can lead to an error of 5%–15% in determining the variations in ice thickness and we propose a new formulation that takes into account the effect of thermal expansion.

Hydrothermal Processing of Microorganisms: Mass Spectral Signals of Degraded Biosignatures for Life Detection on Icy Moons.

Life detection missions to the outer solar system are concentrating on the icy moons of Jupiter and Saturn and their inferred subsurface oceans. Access to evidence of habitability, and possibly even life, is facilitated by the ejection of subsurface material in plumes and outgassing fissures. Orbiting spacecraft can intersect the plume material or detect past sputtered remnants of outgassed products and analyze the contents using instruments such as mass spectrometers. Hydrothermalism has been proposed for the subsurface environments of icy moons, and the organic remains of any associated life would be expected to suffer some degradation through hydrothermalism, radiolysis, or spacecraft flyby impact fragmentation. Hydrothermalism is treated here for the first time in the context of the Europa Clipper mission. To assess the influence of hydrothermalism on the ability of orbiting mass spectrometers to detect degrading signals of life, we have subjected Earth microorganisms to laboratory hydrothermal processing. The processed microorganism samples were then analyzed using gas chromatography–mass spectrometry (GC–MS), and mass spectra were generated. Certain compound classes, such as carbohydrates and proteins, are significantly altered by hydrothermal processing, resulting in small one-ring and two-ring aromatic compounds such as indoles and phenols. However, lipid fragments, such as fatty acids, retain their fidelity, and their provenance is easily recognized as biological in origin. Our data indicate that mass spectrometry measurements in the plumes of icy moons, using instruments such as the MAss Spectrometer for Planetary Exploration (MASPEX) onboard the upcoming Europa Clipper mission, can reveal the presence of life even after significant degradation by hydrothermal processing has taken place.

The influence of heterogeneous seafloor heat flux on the cooling patterns of Ganymede’s and Titan’s subsurface oceans

Several icy moons of Jupiter and Saturn are known to possess deep water oceans. Heating in the rocky mantle underneath often produces heterogeneous heat flux patterns at the ocean’s seafloor. How this internal ocean dynamically relates the seafloor to the surface ice shell is a crucial question to understand the long term evolution of icy moons. Here we investigate how a heterogeneous seafloor heat flux pattern affects the convection and heat transfer in the subsurface ocean of large icy worlds involving a high pressure ice layer beneath the seafloor such as Titan or Ganymede. We perform rotating convection simulations in a thin 3D spherical shell with a prescribed heterogeneous bottom heat flux inferred from 3D convection simulations of the underlying mantle (Choblet et al., 2017b). In our simulations, although the amplitude of imposed inner boundary heat flux heterogeneity is rather moderate, preferred longitudes of intense outer boundary heat flux are highly correlated with longitudes of intense inner boundary heat flux. In addition, a small imposed inner boundary large-scale order 2 pattern is amplified at the outer boundary heat flux by the convection in the thin shell. Lastly, deviations from axisymmetry and equatorial symmetry in the outer boundary heat flux increase with the main convection vigor and the amplitude of the inner boundary heterogeneity. In our models polar vs. equatorial cooling is mostly controlled by inertial effects, as was found by Amit et al. (2020) for homogeneous boundary conditions, with the latitudinally equilibrated inner boundary heterogeneity acting to reduce the amplitude of this effect. Our results support polar cooling for Titan’s sub-surface ocean.

Water-Group Pickup Ions From Europa-Genic Neutrals Orbiting Jupiter.

Water‐group gas continuously escapes from Jupiter's icy moons to form co‐orbiting populations of particles or neutral toroidal clouds. These clouds provide insights into their source moons as they reveal loss processes and compositions of their parent bodies, alter local plasma composition, and act as sources and sinks for magnetospheric particles. We report the first observations of H2 + pickup ions in Jupiter's magnetosphere from 13 to 18 Jovian radii and find a density ratio of H2 +/H+ = 8 ± 4%, confirming the presence of a neutral H2 toroidal cloud. Pickup ion densities monotonically decrease radially beyond 13 R J consistent with an advecting Europa‐genic toroidal cloud source. From these observations, we derive a total H2 neutral loss rate from Europa of 1.2 ± 0.7 kg s−1. This provides the most direct estimate of Europa's H2 neutral loss rate to date and underscores the importance of both ion composition and neutral toroidal clouds in understanding satellite‐magnetosphere interactions.

Reactive scattering of water group ions on ice surfaces with relevance to Saturn's icy moons

Collisions of hyperthermal water group ions with ices are known to occur in astrophysical environments, for example, solar wind-comet interactions and moon-magnetosphere interactions (at Saturn and Jupiter), yet their effect on surface and gaseous composition is little understood. Here, we report molecular dynamics simulations of hyperthermal water-group molecules impacting water-ice surfaces using the ReaxFF reactive force fields to describe bond breaking and forming processes dynamically during the reactive collision events. Simulation conditions are chosen for relevance to Saturn's moons Dione and Rhea. At impact velocities of 10–35 kms−1 (8 to 102 eV for O), we find that water group projectiles undergo Eley-Rideal reactions with the ice surface to form O2, HO2, and H2O2. At a 45o angle of incidence the OO bonded products tend to embed within a few molecular layers of the surface. Smaller angles of incidence lead to formation of some molecular oxygen that promptly rebounds from the surface with ~3 eV kinetic energy. Impact velocity, angle of incidence, and hydrogenation of the impactor strongly influence O2 formation, with the yield peaking at 19% for atomic oxygen impactors at 20 kms−1. Notably, this reaction is relatively temperature independent and proceeds in hydrogen rich pristine ice, where radiolysis is hindered. This mechanism for O2 production from low energy impacts may contribute to O2 exospheres at Saturn and Jupiter's icy moons, where hyperthermal ion fluxes are large.

Toward Detecting Polycyclic Aromatic Hydrocarbons on Planetary Objects with ORIGIN

Abstract Polycyclic aromatic hydrocarbons (PAHs) are found on various planetary surfaces in the solar system. They are proposed to play a role in the emergence of life, as molecules that are important for biological processes could be derived from them. In this work, four PAHs (pyrene, perylene, anthracene, and coronene) were measured using the ORganics Information Gathering INstrument system (ORIGIN), a lightweight laser desorption ionization-mass spectrometer designed for space exploration missions. In this contribution, we demonstrate the current measurement capabilities of ORIGIN in detecting PAHs at different concentrations and applied laser pulse energies. Furthermore, we show that chemical processing of the PAHs during measurement is limited and that the parent mass can be detected in the majority of cases. The instrument achieves a 3σ detection limit in the order of femtomol mm−2 for all four PAHs, with the possibility of further increasing this sensitivity. This work illustrates the potential of ORIGIN as an instrument for the detection of molecules important for the emergence or presence of life, especially when viewed in combination with previous results by the instrument, such as the identification of amino acids. ORIGIN could be used on a lander or rover platform for future in situ missions to targets in the solar system, such as the icy moons of Jupiter or Saturn.

A global system of furrows on Ganymede indicative of their creation in a single impact event

Furrows are a concentric system of tectonic troughs, and are the oldest recognizable surface feature on Ganymede. We analyzed the distribution of furrows utilizing Voyager and Galileo images and found that furrows over Ganymede's surface are part of a global concentric circular structure. If this multi-ring structure is impact origin, this is the largest impact structure identified so far in the solar system. Deviations of the shapes of the furrows from the concentricity are small everywhere, which implies that the relative location of the blocks of the dark terrains over the entire surface of Ganymede has not changed appreciably even during formation of the bright terrains. The estimate of the impactor size is difficult, but an 150 km-radius impactor is consistent with the observed properties of furrows. The furrow-forming impact should have significant effects on the satellite's geological and internal evolution, which are expected to be confirmed by future explorations of Jupiter's icy moons, such as the JUICE (Jupiter Icy moon Explorer) or Europa Clipper mission.

Factoring Origin of Life Hypotheses into the Search for Life in the Solar System and Beyond.

Two widely-cited alternative hypotheses propose geological localities and biochemical mechanisms for life’s origins. The first states that chemical energy available in submarine hydrothermal vents supported the formation of organic compounds and initiated primitive metabolic pathways which became incorporated in the earliest cells; the second proposes that protocells self-assembled from exogenous and geothermally-delivered monomers in freshwater hot springs. These alternative hypotheses are relevant to the fossil record of early life on Earth, and can be factored into the search for life elsewhere in the Solar System. This review summarizes the evidence supporting and challenging these hypotheses, and considers their implications for the search for life on various habitable worlds. It will discuss the relative probability that life could have emerged in environments on early Mars, on the icy moons of Jupiter and Saturn, and also the degree to which prebiotic chemistry could have advanced on Titan. These environments will be compared to ancient and modern terrestrial analogs to assess their habitability and biopreservation potential. Origins of life approaches can guide the biosignature detection strategies of the next generation of planetary science missions, which could in turn advance one or both of the leading alternative abiogenesis hypotheses.

Five decades of radioglaciology

AbstractRadar sounding is a powerful geophysical approach for characterizing the subsurface conditions of terrestrial and planetary ice masses at local to global scales. As a result, a wide array of orbital, airborne, ground-based, and in situ instruments, platforms and data analysis approaches for radioglaciology have been developed, applied or proposed. Terrestrially, airborne radar sounding has been used in glaciology to observe ice thickness, basal topography and englacial layers for five decades. More recently, radar sounding data have also been exploited to estimate the extent and configuration of subglacial water, the geometry of subglacial bedforms and the subglacial and englacial thermal states of ice sheets. Planetary radar sounders have observed, or are planned to observe, the subsurfaces and near-surfaces of Mars, Earth's Moon, comets and the icy moons of Jupiter. In this review paper, and the thematic issue of theAnnals of Glaciologyon ‘Five decades of radioglaciology’ to which it belongs, we present recent advances in the fields of radar systems, missions, signal processing, data analysis, modeling and scientific interpretation. Our review presents progress in these fields since the last radio-glaciologicalAnnals of Glaciologyissue of 2014, the context of their history and future prospects.

Desert cyanobacteria under space and planetary simulations: a tool for searching for life beyond Earth and supporting human space exploration

AbstractThe astonishing capability of life to adapt to extreme conditions has provided a new perspective on what ‘habitable’ means. On Earth extremophiles thrive in hostile habitats, such as hot and cold deserts or Antarctic sub-glacial lakes considered as Earth analogues of Mars and icy moons of Jupiter and Saturn. Recently desert cyanobacteria were exposed to ground-based simulations of space and Martian conditions and to real space and Martian conditions simulated in low Earth orbit using facilities attached outside the International Space Station. When exposure to such conditions does not exceed repair capabilities, more data are available regarding the physico-chemical constraints that life can withstand. When the accumulated damage exceeds the survival potential, the persistence of biomarkers contributes to the search for life elsewhere. Knowledge concerning the endurance of desert cyanobacteria under space and Martian conditions contributes to the development of life support systems.

Cryo-braking using penetrators for enhanced capabilities for the potential landing of payloads on icy solar system objects

The icy moons of Jupiter and Saturn are important astrobiology targets. Access to the surface of these worlds is made difficult by the high ΔV requirements which is typically in the hypervelocity range. Passive braking systems cannot be used due to the lack of an atmosphere, and active braking by rockets significantly adds to the missions costs. This paper demonstrates that a two-stage landing system can overcome these problems and provide significant improvements in the payload fraction that can be landed The first stage involves a hypervelocity impactor which is designed to penetrate to a depth of a few tens of meters. This interaction is the cryo-breaking component and is examined through laboratory experiments, empirical relations and modeling. The resultant ice-particle cloud creates a transient artificial atmosphere that can be used to enable passive braking of the second stage payload dd, with a substantially higher mass payload fraction than possible with a rocket landing system.It is shown that a hollow cylinder design for the impactor can more efficiently eject the material upwards in a solid cone of ice particles relative to solid impactors such as spheres or spikes. The ejected mass is shown to be of the order of 103 to 104 times the mass of the impactor. The modeling indicates that a 10 kg payload with a braking system of 3 m2 (i.e. an areal density of 0.3 kg/m2) is sufficient to allow the landing of the payload with the deceleration limited to less than 2000 g's. Modern electronics can withstand this deceleration and as such the system provides an important alternative to landing payloads on icy solar system objects.

Effect of water activity on rates of serpentinization of olivine

The hydrothermal alteration of mantle rocks (referred to as serpentinization) occurs in submarine environments extending from mid-ocean ridges to subduction zones. Serpentinization affects the physical and chemical properties of oceanic lithosphere, represents one of the major mechanisms driving mass exchange between the mantle and the Earth’s surface, and is central to current origin of life hypotheses as well as the search for microbial life on the icy moons of Jupiter and Saturn. In spite of increasing interest in the serpentinization process by researchers in diverse fields, the rates of serpentinization and the controlling factors are poorly understood. Here we use a novel in situ experimental method involving olivine micro-reactors and show that the rate of serpentinization is strongly controlled by the salinity (water activity) of the reacting fluid and demonstrate that the rate of serpentinization of olivine slows down as salinity increases and H2O activity decreases.

New Images Give More Proof for Europa's Plumes

Researchers used a modified version of a technique for discovering exoplanets to view Jupiter's icy moon in a new light.

Fracturing and flow: Investigations on the formation of shallow water sills on Europa

Double ridge tectonic features appear prominently and ubiquitously across the surface of Jupiter's icy moon Europa. Previous studies have interpreted flanking fractures observed along some of the ridges as indicators of stress resulting from the ridge loading and flexing of the ice shell above a shallow water body. Here, we investigate a shallow water sill emplacement process at a time when the shell is cooling and thickening and explore the conditions that would make such a system feasible on timescales of ridge formation. Results show that fracture initiation and transport of ocean water to shallow depths can realistically occur, although horizontal fracturing and sill lifetimes prove challenging. Finite element models demonstrate that mechanical layering or a fractured shell do not provide enough stress change to promote horizontal fracturing, but tidal forcing does result in a small amount of turn. Assuming it is possible for a shallow sill to form, a sill would convect internally and conduct heat out quickly, resulting in a short lifetime in comparison to an estimated flexure timeframe of 100kyr suggested required for double ridge formation. Consideration of heat transfer and residence in the overlying ice, however, extends the flexure timeframe and multiple sill intrusions or replenishment with warm ocean water could prolong the effective sill lifetime. Though challenges still remain for sill formation at Europa, these analyses constrain the potential mechanisms for emplacement and indicate sills can act as viable options for supplying the heat needed for surface flexure. Further analyses and future missions to Europa will help to increase our understanding of these enigmatic processes.

Mineralogy and astrobiology detection using laser remote sensing instrument.

A multispectral instrument based on Raman, laser-induced fluorescence (LIF), laser-induced breakdown spectroscopy (LIBS), and a lidar system provides high-fidelity scientific investigations, scientific input, and science operation constraints in the context of planetary field campaigns with the Jupiter Europa Robotic Lander and Mars Sample Return mission opportunities. This instrument conducts scientific investigations analogous to investigations anticipated for missions to Mars and Jupiter's icy moons. This combined multispectral instrument is capable of performing Raman and fluorescence spectroscopy out to a >100 m target distance from the rover system and provides single-wavelength atmospheric profiling over long ranges (>20 km). In this article, we will reveal integrated remote Raman, LIF, and lidar technologies for use in robotic and lander-based planetary remote sensing applications. Discussions are focused on recently developed Raman, LIF, and lidar systems in addition to emphasizing surface water ice, surface and subsurface minerals, organics, biogenic, biomarker identification, atmospheric aerosols and clouds distributions, i.e., near-field atmospheric thin layers detection for next robotic-lander based instruments to measure all the above-mentioned parameters.

A permanent, asymmetric dust cloud around the Moon.

Interplanetary dust particles hit the surfaces of airless bodies in the Solar System, generating charged and neutral gas clouds, as well as secondary ejecta dust particles. Gravitationally bound ejecta clouds that form dust exospheres were recognized by in situ dust instruments around the icy moons of Jupiter and Saturn, but have hitherto not been observed near bodies with refractory regolith surfaces. High-altitude Apollo 15 and 17 observations of a 'horizon glow' indicated a putative population of high-density small dust particles near the lunar terminators, although later orbital observations yielded upper limits on the abundance of such particles that were a factor of about 10(4) lower than that necessary to produce the Apollo results. Here we report observations of a permanent, asymmetric dust cloud around the Moon, caused by impacts of high-speed cometary dust particles on eccentric orbits, as opposed to particles of asteroidal origin following near-circular paths striking the Moon at lower speeds. The density of the lunar ejecta cloud increases during the annual meteor showers, especially the Geminids, because the lunar surface is exposed to the same stream of interplanetary dust particles. We expect all airless planetary objects to be immersed in similar tenuous clouds of dust.

Plate tectonics on ice

Jupiter's icy moon Europa is criss-crossed by extensional features. A tectonic reconstruction suggests that Europa's extension is balanced by subduction — if so, Earth may not be the only planetary body with a plate tectonic system.