Enceladus, one of Saturn’s icy moons, exhibits dynamic cryovolcanic activity through plumes of water vapour and ice erupting from its south polar terrain. Understanding the variability of these plumes is essential for interpreting Cassini observations and planning for future missions. This thesis investigates whether temporal variations in plume activity can be explained by coupled processes of deposition, wall accretion and sublimation within subsurface channels. To address this, a two-phase computational fluid dynamics (CFD) framework was developed by extending an OpenFOAM solver to incorporate wall interactions. Parametric studies were performed across a range of boundary conditions. It demonstrated that wall accretion and sublimation act as competing mechanisms that progressively narrow or widen the vents over time. These geometric evolutions feed back into plume dynamics, modulating supersaturation and nucleation phenomena. Comparison with Cassini data suggests that vent-scale processes captured by this model can reproduce key features of observed variability.

The Cassini mission discovered the existence of plumes on the surface of Enceladus. These plumes have been recreated in a laboratory to experimentally investigate the properties of the plumes. This research project focuses on the detection of solid ice particles ejected from an experimental model of the Plumes of Enceladus. The research begins by establishing a baseline experiment in which the detection technique is to be applied. The results from the preliminary investigation, including both the experimental and simulation models, indicate several possibilities of nucleation occurring within the channel. The concept generation phase yielded two general detection principles to be assessed for trade-off analysis: optical methods and impulse-based methods. As a result of the trade-off, an impulse-based method using piezoelectric sensor – a method based on the measurement of impulse caused by the impact of solid particles onto the sensor surface – was selected to be the most appropriate technique for this application. To test the selected detection method, the test campaign was conducted in two phases: drop test and plume model test. The drop test was conducted to investigate the response of the sensor using grains of known masses and variable drop height. A linear relationship between the grain impulse and the voltage response was identified, and this result allowed the impulse of an incident particle to be extrapolated given a voltage response. The second phase of the test campaign integrated the detection system into the plume mode in the vacuum chamber. Several waveforms were detected throughout the experiment: damped wave, attributed to solid particles ejected from the model, turbulent wave, attributed to an unsteady flow of vapor during the initial boiling phase, and low-amplitude periodic waves, attributed to a flock of small particles ejected from the plume model. These results indicate the presence of solid particles in the plume model, and given a particle velocity, the particle size may be determined. A noise analysis of the sensor in the plume model was performed, yielding a plot of the minimum detectable particle size to the particle velocity.

This work presents a kinetic Monte Carlo model to simulate noble gas retention in amorphous solid H2₂O–CO2₂ ice mixtures under varying thermal conditions. Calibrated with experimental temperature-programmed desorption data and temperature–density relations, the model enables long-term simulations in small (~150 nm) ice grains. It shows efficient noble gas retention at ≤30 K, with significant loss near 40 K. Krypton fractionation occurs mainly in ices formed at these warmer temperatures. Using protosolar gas abundances, the model reproduces the noble gas composition measured in comet 67P/Churyumov–Gerasimenko. Results suggest the comet’s bulk formed near 40 K, while its icy grains may trace back to colder (~10 K) presolar reservoirs, preserving signatures of both local and interstellar environments.

The TROPOspheric Monitoring Instrument (TROPOMI) provides high-resolution, global measurements of carbon monoxide (CO) for environmental pollution monitoring. The Automated Plume Detection and Emission Estimation algorithm (APE), developed by SRON, identifies pollution plumes and estimates emissions based on the satellite data. This study implemented four machine learning algorithms to enhance APE and applied them to 180 steel plant locations for 6 years to estimate the average emissions from detected plumes using the divergence method. The models identified up to 136.1% more plumes than APE. Comparing the estimated emissions with the European Pollutant Release and Transfer Register (E-PRTR) dataset shows the ResNet-44 model achieves the lowest bias (1.20 kg/s) and standard deviation (2.36 kg/s) compared to APE, which had a bias of 3.41 kg/s and a standard deviation of 2.40 kg/s. This demonstrates the potential of machine learning to improve plume detection and emission estimation for remote sensing of pollution from space.

This work examines the mechanical strength of Enceladus’ surface by testing ice analogues that replicate its plume-deposited top layer. Ice grains up to 100 µm were produced with a liquid-nitrogen spraying method and stored at –25 °C and –80 °C to study the effects of temperature and freezer time. The samples were tested under atmospheric and vacuum pressures using an adapted cone indentation method, providing both shear and compressive strength. Under atmospheric pressure, sintering leads to increasing strength with longer freezer time and warmer temperatures, with shear strengths of 20–220 kPa and compressive strengths of 40–475 kPa. In vacuum, a combination of effects result in uniformly weak strengths of ~10 kPa. These results indicate that Enceladus’ surface likely consists of a weak, unconsolidated snowy layer over a partially sintered brittle layer. This has direct implications for the design of future lander missions to Enceladus and other icy moons.

High-mass stars are one of the main drivers that shape the galaxy. Understanding the process through which they form is therefore of the utmost importance. This process, however, is not yet fully understood. Contributing to this field, the ALMAGAL survey has studied over 6000 star-forming regions with a higher resolution than any other survey before. On one hand, this data will help scientists study these obscure regions and draw a clearer picture of the high-mass star-formation process. On the other hand, the sheer volume and complexity of the data produced by this survey is far too great for conventional methods to handle swiftly.

This thesis therefore explores the use of unsupervised machine learning (ML) methods to cluster astrochemical spectra from the ALMAGAL survey. The aim of this thesis is to explore which models are best suited for the task, and to use the resulting clusters to establish a chemical evolutionary sequence for high-mass star-forming regions.....

https://github.com/ javialonso05/MSc-Thesis

The icy plumes that originate from the "tiger stripe" fractures on Enceladus provide a clear view of a potentially habitable ocean beneath the icy moon's icy crust. The Cassini spacecraft confirmed the presence of water and icy particles, establishing this ocean as a critical focus in the search for life. The biggest challenge is understanding how the plumes exit the vent and the effect of the tiny ice particles mixing with the gas in the vacuum of space. This thesis investigates the complex physics and dynamics of these plumes using the Direct Simulation Monte Carlo (DSMC) method, implemented within the OpenFOAM framework, to model the rarefied gas-particle flow. This work provides the fundamental physical context essential for precisely interpreting Cassini spacecraft data, pushing the boundaries of our knowledge about ocean worlds, and guiding future investigations in the search for extraterrestrial life.

Enceladus, a moon of Saturn, is a prime candidate for extraterrestrial life due to its subsurface ocean and organic-rich water plumes, discovered by the Cassini mission. Exploring this potential involves significant challenges due to the harsh and dynamic environment of Enceladus. The moon’s cryogenic temperatures, tectonic activity and uncertain surface textures necessitate robust and reliable means of surface sample acquisition. This thesis introduces an ice sampling system designed for future lander missions to this moon, integrating digital holographic microscopy, microfluidics, and boundary layer pumping to meet these challenges.
The proposed system is controlled by a single rotary actuator, minimizing mechanical complexity and enhancing reliability for deep space operations. It samples, liquefies, and prepares ice for microscopic examination to detect potential microorganisms. The sample is acquired via a conical boundary layer pump and delivered into a microfluidic disk for analysis. The integrated system operates as a single static unit with closed-loop control, enabling precise management of fluid dynamics, and thereby the sample.
The integrated digital holographic microscope provides non-invasive, three-dimensional imaging capa- bilities without mechanical focusing, making it suitable for the extreme conditions on Enceladus. The proof-of-concept prototype demonstrates the system’s feasibility and effectiveness through experimental validation of all subsystems. Additionally, open-source software was developed for processing hologram images, including particle counting and blob analysis.
Future work will focus on adapting this technology for broader terrestrial scientific applications and achiev- ing the necessary technology readiness level for space missions. The system’s robust architecture pro- vides a versatile platform that facilitates the integration of not only microscopy but also a diverse array of other life detection instruments. Consequently, this sampling apparatus represents a viable and innovative solution for the detection of life on Enceladus and other icy worlds.

Saturn's icy moon, Enceladus, has captivated scientists since NASA's Cassini spacecraft discovered massive plumes of water vapour and ice erupting from its south pole. The goal of this study was to present a novel opportunity to characterise the particles in the plumes by searching for optical phenomena such as rainbows and halos in the geysers of Enceladus using Cassini's remote sensing data. During several flybys, we discovered unusual stripe-like patterns within these plumes using simultaneous observations in the Cassini VIMS (Visible and Infrared Mapping Spectrometer) and ISS (Imaging Science Subsystem). This anomaly, unlike any other known optical phenomenon, indicates the presence of an inclined, periodic, millimetre-sized structure in the Saturnian system. We propose two hypotheses for these patterns: they may be caused by a periodic structure in Saturn's Norse group orbits or the E-ring. This unexpected discovery could offer new insights into the particle dynamics within Saturn's environment.

Enceladus, one of the icy moons of Saturn, has been of major scientific interest since the Cassini-Huygens mission has explored the Saturn system. This is due to cryovolcanic geysers with complex organic molecules and other ingredients for life in it blasting into space from its subglacial warm ocean. The moon's harsh environmental conditions require innovative bio-inspired locomotion strategies that enable the exploration of Enceladus. This thesis presents a novel ice adhesion effector based on the thermoelectric effect to create reversible adhesive connections. The effector developed here has a recorded ice adhesive strength of 1.5 MPa; enough to support the small-scale robotic system developed in this thesis. The robotic system combines a tracked locomotion method with the ice adhesion technology, that enables the robot to move continuously on steep inclined ice walls. This new technology can be used for transportation of scientific instruments in extreme environments.

The James Webb Space Telescope (JWST) has observed the leading and trailing hemisphere of Jupiter's largest moon Ganymede in August 2022. The resulting spectra from the Near InfraRed Spectrograph (NIRSpec) are dominated by water ice and CO2 features. At 3.1 micron the spectra show the Fresnel reflection peak of water ice. Analysing this feature gives insight into the crystallinity of water ice on Ganymede's surface. Crystallinity is influenced by temperature, particle bombard-
ment, water vapor deposition and cryovolcanic activity. Therefore, analysing the distribution of the crystallinity of water ice on Ganymede gives inside into energetic processes occurring on the surface of the icy moon as well as the longitudinal and latitudinal variations of these processes.

This study is part of an ongoing research project, which aims to increase the physical understanding of the plume formation on Saturn’s icy moon Enceladus. The experimental setup presented in this study is the third iteration of the physical models aiming to recreate the main plume characteristics, where in this study the effects of the channel length, width, type (straight, converging/diverging or diverging), temperature and material are explored and linked to Enceladus’ crevasses. This is done by conduct- ing experiments with 7 different models, where the temperature and pressure are measured along the channels. The models are placed on top of a water-filled reservoir, where the reservoir conditions can be controlled to a limited extent by varying the heating power supplied to the reservoir water. The experimental setup is placed in the test section of the Hypersonic Test Facility Delft (HTFD), which functions as a vacuum chamber.

It is shown that the varying geometry of the channel imposes constraints on the maximum expansion angle before flow separation occurs, the sonic point location and the length/width combination in order to achieve a certain vent Mach number and mass flow rate, although this is also decided by the reservoir and ambient conditions. However, besides the physical properties of the model, there is evidence that the flow properties are dominated by the thermal processes occurring inside the setup. Condensation occurs only in the reservoir, releasing latent heat and making the isentropic flow assumption invalid by definition. It is demonstrated that it is likely that the thermal radiation from the test section of the HTFD onto the model is sufficient to thermally choke the flow. It is unlikely that the flows become choked due to the effects of friction alone. Cooling the models by 10-15°C did not result in significant changes in flow properties, and to have noticeable effects on the flow, the models would have to be cooled to much lower temperatures so that condensation occurs in the channel instead of the reservoir. Although the vapor remains unsaturated in the channels, there are signs of local temperature spikes in the ex- panding sections of the channels, near the vent, when either no or low heating power is supplied to the reservoir water and the pressure in the channel is reduced. This implies that either the temperature at the center of the channel is lower than what could be expected from the temperature measurements and heat is thus released by the deposition of the vapor, or the particles that condensed in the reser- voir partially evaporate after the throat of the channel, after which the evaporative cooling freezes the remainder of the particles, with the accompanying latent heat release. It is also not expected that a pressurized reservoir is necessary to create the plumes on Enceladus, nor is the presence of a geomet- rical throat, due to the combined effects of friction and condensing vapor. The results of one physical model are compared to a computational fluid dynamics model using the same geometry, and the main difference between the physical and numerical model is that the vent pressure of the numerical model is approximately half the vent pressure of the physical model, and the temperature of the numerical model dropped to about -50°C at the expanding section of the channel where the temperature only increased throughout the channel for the physical model. This, and the small heat spike near the vent under low-power conditions, has questioned the accuracy of the temperature measurement method and further research would be required to improve this accuracy.

A new era of exploration is on the horizon with missions such as the James Webb Space Telescope and the JUpiter Icy Moons Explorer (JUICE), focusing on the enigmatic icy moons within our solar system. Previous missions, like the Cassini-Huygens mission, have provided an invaluable wealth of data regarding Saturnian moons, shedding light on their intricate characteristics. However, despite past studies, a clear link between various surface-altering processes—such as E-ring bombardment, meteoroid impacts, photolysis, dark material, plasma, and energetic electron bombardment—and terrain features has not been fully explored.

This investigation employs the Hapke photometric model to fit the reflectance spectra of the icy moons by using a Least Squares Method algorithm. A novel validation approach is followed by utilizing experimental data obtained from crushed ice particles sourced from the Solid Spectroscopy Hosting Architecture of Databases and Expertise (SSHADE). Additionally, this data serves as a testing ground for innovative techniques in estimating crystallinity based on the 2- and 1.65-micron absorbance features of water ice.

By using data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS), this thesis delves into the characteristics of the icy regolith on moons such as Rhea, Dione, and Enceladus. The analysis encompasses three studies: well-resolved terrain units, variations across an entire moon following their longitudinal lines, and a comparative examination of primary regions affected by various exogenic processes between the different moons.

The results of this study underscore the distinct impacts of each process on the icy regolith. In conclusion, by observing surface features such as grain sizes, crystallinity and surface roughness, it is possible to determine which processes are dominating on the moon's surface. Knowing how these characteristics evolve with time, such observations could also be used to determine (relative) ages of the surface's features.

Mixed ices of carbon dioxide (CO₂) and water (H₂O), prevalent in cometary nuclei, solar system satellites, and interstellar dust particles, have posed a persistent challenge in understanding the fundamental behaviors of carbon dioxide in these icy environments. Specifically, the intriguing shift in the CO₂ stretching fundamental band observed on icy moons like Europa and Ganymede has remained enigmatic. In this study, we undertake a comprehensive investigation to elucidate this phenomenon by characterizing carbon dioxide on Ganymede and Europa through temperature-dependent spectral analyses.

Laboratory experiments involve the study of pure CO₂ ice and its mixtures with water at varying concentrations, mimicking astrophysical conditions. Utilizing temperature-programmed desorption (TPD) and Fourier-transform infrared spectroscopy (FTIR) techniques, coupled with Gaussian deconvolution of obtained spectra, we explore the molecular interactions underlying the observed spectral shifts. Our experiments at 10 K under ultra-high vacuum conditions replicate interstellar medium conditions, providing crucial insights into CO₂ behavior in icy environments.

In the discussion, a detailed overview is presented of the positions and behaviors of the fitted Gaussians for the asymmetric stretching bands of CO₂ in pure form and when co-deposited with water. The temperature-dependent evolution of these bands reveals intricate dynamics, emphasizing the influence of CO₂ concentration on the shifting positions and shapes of the spectral features.

The conclusions highlight key findings, including the complex nature of CO₂ interactions within water ice, manifested in the emergence of multiple peaks at different concentrations. The thermal desorption analyses unveil distinct desorption behaviors, shedding light on the interactions during ice phase transitions. Importantly, our laboratory results align with observations from the James Webb Space Telescope (JWST), providing a synergistic approach to understanding CO₂ behavior on icy worlds. The variations observed in Ganymede’s spectra across latitudes and longitudes further corroborate the influence of temperature and UV irradiation on CO₂ dynamics within the ice.

This study contributes valuable insights into the molecular intricacies of CO₂ in mixed ices, bridging laboratory experiments with observational data. The synergy between these approaches promises a more profound understanding of CO₂ behavior in diverse astrophysical environments, advancing our knowledge of icy worlds in our Solar System and beyond.

In this study, plume experiments were conducted to mimic the thermodynamic conditions on Saturn's moon, Enceladus. The icy moon subsurface ocean and cracks in the surface have been simulated by using a liquid water reservoir and a narrow channel, while the low-pressure environment at Enceladus’ surface was achieved with a vacuum chamber. We aimed to examine how channel temperature affected the plume's behavior, testing two models with differing wall temperatures: room temperature and near 0°C. The colder model better replicated Enceladus' plumes, producing a saturated flow in which icy particles due to nucleation were seen. A conservative 1.5-3% minimum solid fraction is estimated from measurements and modeling. Pitot-tube measurements indicated Mach numbers around 1, with velocities between 400-500 m/s. Flow temperature and velocity closely correlated with wall temperature, indicating effective heat transfer. The study suggests that supersonic plume velocities observed on Enceladus can be achieved through thermal effects within the icy crust's crevasse, without requiring extreme expansion ratios. Additionally, the research provides evidence of the relationship between the crevasse's expansion ratio and the flow and wall temperatures.

Enceladus has all the ingredients to support life in its ocean and is therefore a good place to start looking for extraterrestrial life in our Solar System. To explore Enceladus, a probe is needed that autonomously navigates the extreme, icy and unknown environment. Multiple robotic systems are proposed to explore Enceladus. The concept to be optimised by this research is the Freezing Locomotion Integrated Chain Kinematics (FLICK). This concept uses a track of adhesion links that use state-of-the-art ice locomotion: By melting and freezing the ice with peltier modules integrated into the links, the robot can move over the ice wall. To reach subzero temperatures to freeze the ice, the hot side of the Peltier modules must be cooled. The aim of this research is to optimise the adhesion link design by the replacement of the water cooling system with a Phase Change Material (PCM) cooling system. Utilising the latent heat storage of the PCM, this research provides a solid-state cooling solution. The PCM container was made of aluminium to increase the heat transfer from the Peltier module to the PCM and enable the heat absorbed by the PCM to radiate to the environment. Furthermore, 3 heat fins were used to increase the contact area between the PCM and the container, increasing the available latent heat storage. The cooling performance of various PCMs was tested and the octadecane was found to be the best option, due to its high latent heat capacity and relatively low density. Tests on ice showed ice adhesion with PCM cooling of the Peltier modules was possible. A theoretical model was built to estimate the required octadecane volume to obtain subzero temperatures. 7.457 g of octadecane was integrated into the adhesion link of FLICK. The model of the new link obtained a minimum temperature of -1.1 $\deg$C and subzero cooling time of 45 s, for an ambient temperature of 21 $\deg$C without the presence of ice. Using the designed PCM cooling mechanism, the mass of FLICK's cooling system could be reduced from >1309 g to 375.68 g. However, the system must be built and tested to assess its behaviour and viability. This design assumed Earth conditions. To make the system fit to the cold temperatures and low pressures of Enceladus, the adhesion mechanism should be tested in a cooled vacuum chamber.

This Master thesis consists in investigating the formation and behavior of vapor and ice plumes. These plumes can occur in icy moons of our solar system, such as Europa or Enceladus, which are widely believed to have a liquid water ocean beneath their crust. These plumes most likely consist of a sub- surface reservoir of liquid water fed by the ocean, a crevasse, and a vent at the ice surface. Under certain conditions, the liquid water starts evaporating and, due to the high reservoir pressure, the result- ing vapour starts flowing upwards through the crevasse. Due to the high pressure difference between the reservoir and the vent at near vacuum conditions, supersonic plumes are formed. This work stud- ies the reservoir conditions and plume physics, gathering different models available in literature and comparing them to available data, such as that from observations from Cassini spacecraft. First, a model capable of describing the condensation phenomenon is sought. The effects of the consequent release of latent heat to be absorbed back by the vapour flow are also studied. Grains will then start to nucleate and grow. These particles can either collide and stick to the walls or keep flowing mixed with the vapour. Some of the above mentioned latent heat can be absorbed back by the icy walls of the crevasse and generate more vapour by sublimation. Further, this project also aims to extend the model mentioned above so that it considers the effects of a fully multi-phase, multidimensional flow, checking for the effects of rarefaction and hence the limits of the continuum assumption. Finally, a similarity analysis is performed so that the influence of working with scales as different as the channels used in the laboratory at TU Delft or the real dimensions of the crevasses found in Enceladus can be fully tackled. Any progress on the ongoing investigations about the physical characteristics of these plumes could be crucial to deepen our knowledge on geological mechanisms in icy moons of our solar system. This, in turn, could trigger research on organic compounds present in these moons, perhaps even allowing for the existence of life. Further, the model used throughout this work can be applied to study power production devices where condensation might play an important role, such as steam turbines for light-water-cooled nuclear reactors or turbines proposed to be used in innovative organic Rankine cycle (ORC) configurations, natural gas supersonic separators, supercritical CO2 compressors for large-scale carbon capture and sequestration (CCS) and micro-nozzles.

The Saturnian moon Titan has a methane-based hydrological cycle similar to the water cycle on earth. This includes lakes, fluvial drainage networks, clouds and has evidence for precipitation of methane rain. Here we explore the impact of rainfall on Titan based on an analogue laboratory approach. While the composition and structure of the Titan atmosphere and its cloud systems has been studied by the Cassini-Huygens missions, the chemical composition of rain drops remains undetermined. Recent studies have put forward the possibility of soluble nitrogen within rain drops that were earlier assumed to be purely made of methane. Based on simulations, we find a 77% - 23% distribution of methane and nitrogen. The ratio was used to develop a suitable laboratory analogue approach to study splash erosion by rain drop impacts. Using this analogue approach that involved impacting individual drops on soil sample analogues and custom-built numerical models, we find that that rain drops on Titan can redistribute soil particles at larger distances (30 - 600 mm) than Earth due to different energy transmission percentages from drop to splashed matter (15% - 50% of the drop, in comparison to water). Assuming a particle launch angle of 45◦, soil particles can reach heights of ∼10-70 mm, meaning soil splashing can create visible phenomena and proof for recent rainfall events. Such observables of Titanic rainfall can be used for more detailed surface studies by future missions, such as NASA’s Dragonfly drone.

Crater counting is the main method used to determine the age of a planetary surface. This method relies on knowing the cratering rate to estimate the absolute age of a surface. However, two theories currently exist for impact cratering of the moons in the Saturnian system, one suggesting that the majority of the impactors are of heliocentric origin (i.e. they come from orbits around the Sun), and the other suggesting that the majority of impactors are of planetocentric origin (i.e. they originate from orbits around Saturn). The different theories result in very different surface ages of the icy moons. According to the heliocentric model, the surface of Titan would date to ~3 Ga, while according to the planetocentric model the surface of Titan could be dated between ~15 Ma and ~4 Ga, allowing for much more erosion of the surface according to Bell (2020). Given that these two orbits result in different impact velocities, this work attempts to discover if the impact velocity can be determined for impactors on icy moons based on crater characteristics, such as crater depth and diameter, by recreating impacts in the lab.

Previous impact experiments have been performed with different impactors and target materials. This study aims at expanding previous research by performing tests on icy particles, something not done before. The data obtained from experiments are then used to obtain the estimated impactor diameter that created craters on the surface of these icy moons based on the expected impact velocities. This data can then be used to predict the likelihood of an impactor originating from either a heliocentric or planetocentric orbit.

This work developed several methods to produce impact craters using different instruments and different surfaces. The best results were obtained either with the gas gun and ice blocks or with the drop tower and icy particles. Using the scaling relationships found in this work, it was shown that the required impactor diameter can be obtained from craters on icy moons and that a distinction can be made between planetocentric and heliocentric impactors. However, more work is needed to narrow down the scaling relationship to obtain a reasonable impactor diameter given a certain impact crater. More information about the crater, such as the transition of ice type during an impact, should be used in the future to further constrain the velocity ranges.