ESA JUICE Research Articles

Low temperature phase transitions in the visible and near-infrared (VNIR) reflectance spectra of (NH4)2HPO4 and (NH4)HSO4 salts

The detection of ammonium bearing crystalline solids in salt-water systems on icy bodies and solar system bodies could provide information about the ascent of these salts from a deep reservoir within the hydrosphere. Due to their chemical-physical properties, NH4+ compounds play a key role both in the internal dynamics of celestial bodies and in the potential habitability of ocean worlds. In this work we analysed the reflectance spectra of two synthetic NH4+ salts: ammonium hydrogen phosphate (NH4)2HPO4 and ammonium hydrogen sulphate (NH4)HSO4 in the 1–4.2 μm spectral range at low temperature, between 110 and 290 K. For (NH4)2HPO4 we also examined the effect of three different grain sizes (150–125 μm; 125–80 μm; 80–32 μm). The collected reflectance spectra show absorption features related to NH4+ group overtone and combination modes in the 1–2.5 μm range. In particular, the bands located at ∼1.09 μm (3ν3), ∼1.30 μm (2ν3 + ν4), ∼1.58 μm (2ν3), ∼2.02 μm (ν2 + v3) and ∼ 2.2 μm (v3 + v4) could be useful to discriminate these salts. The low temperature spectra, compared to those at ambient temperature, reveal finer structures, displaying sharper and narrower absorption bands. The selected NH4+-bearing salts are subjected to reversible low temperature phase transitions, which are revealed in the spectra by a progressive growth and shift of the bands toward shorter wavelengths with a drastic change of their depth. We performed laboratory measurements of ammonium (NH4+) compounds to address the limited data available expanding the existing database. The collected cryogenic spectra can be directly compared with remote sensing data from planetary missions of the upcoming decade such as NASA's Europa Clipper, and ESA's JUICE and the newly launched James Webb Space Telescope expanding the existing database of ammonium compounds at cryogenic temperature.

Exploring the initial landing site area of Dragonfly on Titan: Insights into shear failure and strike-slip faulting at Selk crater

Morphologically distinct characteristics of strike-slip deformation have not been well documented on Titan due to limited quality and coverage of observational data. However, optimal shear failure conditions may exist within Titan's shallow subsurface due to the inferred presence of a porous ice layer saturated with liquid hydrocarbons. In this study, we examine the proposed Dragonfly landing site on Titan, the Selk crater region, and investigate the area in context of possible tidal shear deformation and strike-slip faulting. For this, we use established methods of previous studies based on the Coulomb failure criterion and numerical model SatStress to calculate diurnal tidal stresses that may act to deform the region. We extracted stresses along one line of latitude (5°N) from 155°-165° E, crossing various identified geologic terrain units, and found that presently, shear failure initiated through diurnal tidal stresses can only occur if pore fluid pressures are intermediate to high (λ > 0.75) and/or the coefficient of friction of the icy crust is low (μf < 0.3). As it is unlikely for these conditions to be present in this area, we can infer that there is currently no shear deformation occurring in the Selk crater region due to diurnal tidal stresses. The results presented here aim to advance our knowledge of structural crustal properties that promote or limit shear failure on Titan on a local scale, and to better inform the exploration of Titan through the Dragonfly mission. To gain new insights and broaden our understanding of icy worlds, it is imperative that we employ the most precise data in our modeling work. Missions like Dragonfly, Europa Clipper and ESA's JUICE will further constrain our modeling approach and can help pinpoint the most interesting locations for lander exploration and possibly for gaining access to the interior ocean of icy moons.

Tidally induced fault motion within Europa's ice shell and implications for subsurface communication development

The processes that maintain a subsurface ocean at Europa may also cause geophysical hazards within the overlying ice shell that are important to understand for any subsurface access mission. In this study, we applied 3D finite element models to better constrain the potential magnitude of tidally induced fault motion in the ice shell that a cryobot and communication hardware could experience during a subsurface mission. Models showed that displacement along a fault resulting from a static tidal stress at orbital perijove was <5 cm at the subjovian and ∼ 5–82 cm at Thera Macula, depending on fault orientation, changes in tidal stress with depth, and coefficient of friction. Time-dependent tidal forcing over one tidal cycle resulted in fault displacements of ∼0.50–2.9 m for end-member fault geometries at Thera Macula. The potential strain imposed on a communication tether from the fault movement will depend greatly on the currently unknown adhesion of the tether to the ice as well as potential fault tip propagation, yet these analyses provide first-order approximations for end-member strain conditions using measurements of the motion across a fault for a cryobot at 1 km depth. Results suggest it is important to consider motion throughout a tidal cycle and that certain locations and surface features on Europa may prove to be more challenging for a subsurface mission than others. With NASA's upcoming Europa Clipper and ESA's JUICE missions, fault displacements on Europa could be observed, providing further information on regions or features more/less hazardous to cryobot missions.

Characterisation of the main belt asteroid (223) Rosa

Context. The ESA JUICE space mission, on its way to study Jupiter’s environment and icy moons, will pass twice through the main asteroid belt. For this reason, the possibility to perform an asteroid flyby has been investigated. Aims. We aim to gain insight into the physical properties of the outer main belt asteroid (223) Rosa, which has been proposed as a potential JUICE flyby target. Methods. We report new visible and near-infrared spectroscopic observations at different rotation phases. Additionally, we perform a literature review of all the available physical properties, such as diameter, albedo, mass, and rotational period. Results. We find that asteroid Rosa is an X-type asteroid that shows no significant spectral variability combining the new and literature spectroscopic data. Its large size and orbital semimajor axis in the outer main belt indicate that Rosa does not belong to the Themis family, while its albedo is only marginally compatible with the family. Rosa’s estimated density is in agreement with those of other low-albedo X-type asteroids. Hence, we propose that Rosa is a planetesimal that accreted in the protoplanetary disk beyond the snow line.

Estimation of the Ephemerides and Gravity Fields of the Galilean Moons Through Orbit Determination of the JUICE Mission

Jupiter and its moons are a complex dynamical system that include several phenomena like tides interactions, moon’s librations and resonances. One of the most interesting characteristics of the Jovian system is the presence of the Laplace resonance, where the orbital periods of Ganymede, Europa and Io maintain a 4:2:1 ratio, respectively. It is interesting to study the role of the Laplace resonance in the dynamic of the system, especially regarding the dissipative nature of the tidal interaction between Jupiter and its closest moon, Io. The secular orbital evolution of the Galilean satellites, and so the Laplace resonance, is strongly influenced by the tidal interaction between Jupiter and its moons, especially with Io. Numerous theories have been proposed regarding this topic, but they disagree about the amount of dissipation of the system, therefore about the magnitude and the direction of the evolution of the system, mainly because of the lack of experimental data. The future ESA JUICE space mission is a great opportunity to solve this dispute. The data that will be collect during the mission will have an exceptional accuracy, allowing to investigate several aspects of the dynamics the system and possibly the evolution of Laplace Resonance of the Galilean moons. This work will focus on the gravity estimation and orbit reconstruction of the Galilean satellites by precise orbit determination of the JUICE mission during the Jovian orbital phase using radiometric data.

Planning operations in Jupiter’s high-radiation environment: optimization strategies from Juno-ultraviolet spectrograph

The Juno Ultraviolet Spectrograph (Juno-UVS) is a remote-sensing science instrument onboard the Juno spacecraft that has been in polar orbit around Jupiter since July 2016. Juno-UVS measures photon events in the ultraviolet from 68 to 210 nm. It is primarily used to observe emission from the Jovian aurorae but is also sensitive to other sources, such as UV-bright stars, sky background Lyman-alpha emission, and reflected sunlight. However, Juno-UVS is also sensitive to the effects of penetrating high-energy radiation, which results in elevated count rates as measured by the instrument detector array. This radiation presents a challenge for efficiently planning the acquisition of mission science data, as data volume is a valuable (and finite) resource that can quickly be filled when the spacecraft periodically passes through regions of high radiation. This background radiation has been found to vary significantly on both short (spacecraft spin-modulated) timescales, as well as longer timescales from minutes to hours during each close approach to Jupiter. This variability has required a multipronged approach in the operation planning of hardware (such as, dynamic instrument voltage adjustment) as well as onboard software (such as, utilizing data quality factors for the selective storage of science data). We present an overview of these current mitigation/optimization techniques and planning strategies used for this instrument, which will likely also be useful for the development and operations of future instruments within high radiation space environments (e.g., the ESA JUICE mission or NASA’s Europa Clipper).

The upper atmosphere of Venus: Model predictions for mass spectrometry measurements

Venus is the closest and most similar planet to Earth in the whole solar system, yet, basic measurements are missing. The atmospheric composition has been studied to some extent with the Pioneer Venus Orbiter mission and the more recent Venus Express, however, the concentration of many species and their isotopic ratios are not yet known with satisfying accuracy. Especially when it comes to the heavy noble gases as Kr and Xe, there is little to no collected data in this field. These elements form a key link to the reconstruction of the atmospheric evolution, which would deliver crucial information on the formation of Earth-like bodies. Knowing the abundances of the noble gases may allow us to answer the question why Venus did not evolve to a potentially habitable planet like its neighbour Earth.This paper presents a meta-study of existing observations of Venus' upper atmosphere and exosphere and an exospheric model of the thermal and hot atmosphere of Venus above the homopause. Mass spectra for possible future Venus missions are predicted, as for example the EnVision mission of ESA. The main focus are the heavy noble gases and requirements for the trajectories are proposed. In addition, mass spectra and recommended integration times for the Venus flyby of ESA's JUICE mission are derived.

BOL and EOL Characterization of Azur 3G Lilt Solar Cells for ESA Juice Mission

In the present paper, we describe the results of electrical characterization of AZUR SPACE triple-junction solar cells at a sun light intensity of 3.7% AM0 and temperatures down to −150°C. At these conditions, which are relevant for the anticipated ESA JUICE mission, the cell efficiency reaches 33.5 % at BOL. Special attention has been paid to the establishing of an in-situ characterization procedure for defining EOL cell characteristics after electron and proton irradiation at low temperature low intensity condition. It was shown that solar cells irradiated at low temperature exhibit a strong recovery effect within short time after stopping the irradiation whereas the absolute value of the recovery depends on the irradiation fluence and particle type. Further on, it was demonstrated that the degradation of the maximum power, Pmp, is much stronger than the degradation of Isc and Voc values. Experimentally defined remaining factors for electron and proton irradiation and the quantification of the observed recovery effects allow a realistic prediction of the solar cell performance at JUICE mission conditions and are essential for the planned solar cell qualification activities.

Radar probing of Jovian icy moons: Understanding subsurface water and structure detectability in the JUICE and Europa missions

Radar probing of Jovian icy satellites is fundamental for understanding the moons' origin and their thermal evolution as potential habitable environments in our Solar System. Using the current state of knowledge of the geological and geophysical properties of Ganymede, Europa and Callisto, we perform a comprehensive radar detectability study to quantify the exploration depth and the lower limit for subsurface identification of water and key tectonic structural elements. To achieve these objectives, we establish parametric dielectric models that reflect different hypotheses on the formation and thermal evolution of each moon. The models are then used for FDTD radar propagation simulations at the 9-MHz sounding frequency proposed for both ESA JUICE and NASA Europa missions. We investigate the detectability above the galactic noise level of four predominant subsurface features: brittle-ductile interfaces, shallow faults, brine aquifers, and the hypothesized global oceans. For Ganymede, our results suggest that the brittle-ductile interface could be within radar detectability range in the bright terrains, but is more challenging for the dark terrains. Moreover, understanding the slope variation of the brittle-ductile interface is possible after clutter reduction and focusing. For Europa, the detection of shallow subsurface structural elements few kilometers deep (such as fractures, faults and brine lenses) is achievable and not compromised by surface clutter. The objective of detecting the potential deep global ocean on Europa is also doable under both the convective and conductive hypotheses. Finally, for Callisto, radar waves can achieve an average penetration depth of ∼15km, although the current understanding of Callisto's subsurface dielectric properties does not suggest sufficiently strong contrasts to produce unambiguous radar returns.

Planetary space weather: scientific aspects and future perspectives

In this paper, we review the scientific aspects of planetary space weather at different regions of our Solar System, performing a comparative planetology analysis that includes a direct reference to the circum-terrestrial case. Through an interdisciplinary analysis of existing results based both on observational data and theoretical models, we review the nature of the interactions between the environment of a Solar System body other than the Earth and the impinging plasma/radiation, and we offer some considerations related to the planning of future space observations. We highlight the importance of such comparative studies for data interpretations in the context of future space missions (e.g. ESA JUICE; ESA/JAXA BEPI COLOMBO). Moreover, we discuss how the study of planetary space weather can provide feedback for better understanding the traditional circum-terrestrial space weather. Finally, a strategy for future global investigations related to this thematic is proposed.