181 research outputs found
Simultaneous inversion for the Earth's mantle viscosity and ice mass imbalance in Antarctica and Greenland
No full textRedistribution of mass in the Earth due to Pleistocene deglaciation and to present-day glacial melting induces secular changes in the Earth's gravitational field. The Earth is affected today by the former mechanism because of the viscous memory of the mantle and by the latter because of ongoing surface mass redistribution and related elastic response. A self-consistent procedure allows us to invert simultaneously for the lower and upper mantle viscosity and for the present-day mass imbalance in Antarctica and Greenland using the observed time variations of the long-wavelength gravity field from satellite laser ranging (SLR) analyses. The procedure is based on our normal mode relaxation theory for the forward modeling and a newly developed inversion scheme based on the Levenberg-Marquardt method. We obtain a large viscosity increase across the 670-km depth transition zone separating the upper and the lower mantle, with the lower mantle viscosity varying over the range 5 × 1021 to 1022 Pa s and the less resolved upper mantle viscosity of the order of 1020 Pa s. When Antarctica is the only present-day source, its rate of melting is ?240 Gt yr?1, corresponding to a sea level rise of 0.7 mm yr?1; when Greenland is added as a source of ice loss, the rates of melting are ?280 Gt yr?1 for Antarctica and ?60 Gt yr?1 for Greenland, corresponding to sea level rises of 0.8 and 0.2 mm yr?1. SLR data indicate that ice melting in the polar regions of the Earth is ongoing.Space EngineeringAerospace Engineerin
Workshop Centrale ELO naar Blackboard 9.1 (ELO Platform)
No full textStijnen, L.L.A., Schumacher, J. & Wagemans, L.J.J.M. (2011). Workshop Centrale ELO naar Blackboard 9.1 (ELO Platform). Maart, 31, 2011, Heerlen: Open Universiteit.Het project Upgrade Blackboard dat in 2011 is uitgevoerd, heeft tot doel te upgraden naar versie 9.1. Om een idee te krijgen wat er nieuw is in versie 9.1 van Blackboard bevat de workshop voor medewerkers van IPO (Instellingsbreed programma onderwijs) verschillende activiteiten die ze zelfstandig kunnen uitvoeren. Door dat te doen, ervaren de medewerkers wat er nieuw is in Blackboard 9.1 en raken ze alvast enigszins vertrouwd met de nieuwe omgeving
Interplanetary laser ranging: Analysis for implementation in planetary science missions
No full textMeasurements of the motion of natural (and artificial) bodies in the solar system provide key input on their interior structre and properties. Currently, the most accurate measurements of solar system dynamics are performed using radiometric tracking systems on planetary missions, providing range measurement with an accuracy in the order of 1 m. Laser ranging to Earth-orbiting satellites equipped with laser retroreflectors provides range data with (sub-)cm accuracy. Extending this technology to planetary missions, however, requires the use of an active space segment equipped with a laser detector and transmitter (for a two-way system). The feasibility of such measurements have been demonstrated at planetary distances, and used operationally (with a one-way system) for the Lunar Reconaissance Orbiter (LRO) mission. The topic of this dissertation is the analysis of the application of interplanetary laser ranging (ILR) to improve the science return from next-generation space missions, with a focus on planetary science objectives. We have simulated laser ranging data for a variety of mission and system architectures, analyzing the influence of both model and measurement uncertainties. Our simulations show that the single-shot measurement precision is relatively inconsequential compared to the systematic range errors, providing a strong rationale for the consistent use of single-photon signal-intensity operation. We find that great advances in planetary geodesy (tidal, rotational characteristics, etc.) could be achieved by ILR. However, the laser data should be accompanied by commensurate improvements in other measurements and data analysis models to maximize the system's science return. The science return from laser ranging data will be especially strong for planetary landers, with a radio system remaining the preferred choice for many orbiter missions. Furthermore, we conclude that the science case for a one-way laser ranging is relatively weak compared to next-generation radiometric tracking systems, requiring the development of much more accurate space-based clocks.Space EngineeringAerospace Engineerin
The feasibility of in-situ observations of Europa's water vapour plumes.
No full textEuropa, the second of Jupiter’s Galilean moons, has attracted strong interest from the scientific community. This is because it could harbour a sub-surface ocean of liquid water beneath its icy surface, which could be habitable. Recent observations indicate the existence of water vapour plumes at Europa’s south pole. The in-situ measurements of the plume particles (both neutral and ionized) may allow the direct sampling of Europa’s (potentially habitable) sub-surface ocean environment, without the need of an expensive landing or surface-ice penetrating mission. The instrument that could be able to perform in-situ sampling of the plumes is PEP (Particle Environment Package). PEP has been selected to fly on-board the European Space Agency's JUICE mission (JUpiter ICy moons Explorer) to be launched in 2022. PEP is under development now at the Swedish Institute of Space Physics (Institutet för rymdfysik or IRF) in Kiruna, Sweden. PEP is an instrument suite with six sensors to characterize the plasma and neutral environment in the Jovian system in-situ and remotely (via fast neutral imaging). The JUICE mission will perform two flybys of Europa. Related to the development of PEP and future observations of Europa’s plumes a Master’s thesis project with the following goal has been proposed: “Determine if PEP can observe Europa's water vapour plume by modelling: (a) the trajectories of neutral and ionized particles from Europa’s water vapour plumes with test-particle simulations and (b) the respective instrument observation.” In the test-particle simulations method the trajectories of particles through background electric and magnetic fields are determined by treating each particle as an isolated test particle. The project focusses on the JDC (Jovian plasma Dynamics and Composition analyser) and NIM (Neutral and Ion Mass Spectrometer) sensors that are part of PEP. We developed a model of the neutral and ionized plume particle environment. We simulated observations of these particles with respectively the NIM and JDC sensor, and demonstrated observations of plume particles is possible even for plumes that have lower mass flux (? 1 kg/s) than what has been observed (7000 kg/s). The developed neutral plume particle model is applicable when the particles in the plume are non-collisional. The ionized plume particle model is applicable to the case where the plume ion density is lower than the typical ion density at Europa. This limits the applicability to plumes with a mass flux ? 1 kg/s. We argue that future Europa plume models should consider the collisions between plume particles. Furthermore the expected high ion density will strongly influence the electric fields at Europa, this effect should be taken into account.Astrodynamics and space missionsSpace flightAerospace Engineerin
Mapping the thickness of the Martian elastic lithosphere using maximum likelihood estimation
No full textThe outermost strong part of a planet is called the lithosphere. When loads, such as volcanoes, sediments, or intrusions, are applied to the lithosphere, it flexes. The amount of flexure is controlled by the flexural rigidity of the lithosphere. The elastic thickness Te is the thickness of an equivalent fully elastic spherical shell which flexes in the same way as the real lithosphere. It is an important quantity because it strongly depends on the lithospheric heat flux at the time that the load was applied, which is controlled by the thermal evolution of the planet and varies in space and time. The loads and the associated lithospheric deflections cause gravity anomalies and topographic relief. Observations of these can be used to constrain Te. In this study, a global map of the elastic thickness of Mars is presented. Several recent missions to Mars have provided global spherical harmonics data sets of gravity and topography. These data are inverted for the shape of the crust-mantle boundary, or equivalently the crustal thickness. This is assuming that all gravity anomalies are caused by only two density interfaces which are the surface and the crust-mantle boundary. The large amplitudes of the Martian gravity field necessitate the application of a finite amplitude correction. A simple, but realistic model, which allows loading and compensation at the same two interfaces, is derived. It uses the differential equations for the flexure of a thin elastic shell and depends on six parameters: the elastic thickness Te, the ratio F of the amplitude of the loads at the two interfaces before flexure, the correlation r between these loads, and three parameters of a covariance function of the isotropic Matérn class which describes the topography before flexure. The input data are localized to specific grid points of a map using multitaper spectral estimation. Contrary to most elastic thickness studies which compute observed and modelled admittance or coherence to find a best-fit solution for Te, this study uses maximum likelihood estimation as first proposed by Simons and Olhede (2013). This technique allows to determine the parameter set which is most likely to have produced the localized estimates of the topography and the shape of the crust-mantle boundary. Maps of the most likely parameter sets are presented for different localization window sizes. The results generally agree with previous studies, yielding Te ~10km in the southern uplands and higher values at the large volcanoes. This also corresponds to thermal evolution models predicting a more rigid lithosphere in more recently formed areas. Log-likelihood contours and Monte Carlo simulations with synthetically generated topographies reveal the quality of the results. The elastic thickness is well constrained in the southern uplands and at Elysium and Ascraeus Mons, but poorly constrained in the northern lowlands and at the other volcanoes. While this study shows that it is possible to retrieve Te with maximum likelihood estimation, more research is needed to explain these poor constraintsCivil Engineering and GeosciencesGeoscience and Remote Sensin
Modelling the orbital-tidal evolution of the Galilean moon Io
No full textIo, the innermost Galilean moon of Jupiter, is the most volcanically active body in the Solar System. Its volcanism is driven by tidal foces, which are in turn sustained by the Laplace resonance between Io, Europa, and Ganymede. Tides have significant impact on a body's characteristics. The liquid ocean underneath Europa's icy surface is sustained by tidal heating. Similarly, tidally-heated exomoons may be able to support life well outside the habitable zone. Tidal forces influence the orbital evolution of a body. Consequently, the orbital evolution also affects the tidal evolution. Thus, it is important to understand how tides drive the Jupiter system and how sustainable the tidal heating that Io experiences is. Additionally, the interior structure of both Jupiter and Io are not very well understood nor constrained, but govern the orbital-tidal evolution via the Love number k2 and the quality factor Q. The orbital motion and tidal evolution of the Jupiter system was modelled. For this, existing TUDAT functions, for example for third-body gravitational acceleration, were combined with new tidal acceleration models. To enable long-term stability and fast computation of the integration a 4 th -order symplectic integrator with Wisdom-Holman split was applied. This type of energy-conserving integrator has limited applicability in the case of small dissipative forces, but requires fewer force evaluation than, for example, a Runge-Kutta integrator of the same order. A variety of reasonable values for k2 and Q have been tested, as well as extreme cases. It was found that the tides raised on Jupiter by Io have a negligible effect on the evolution of the system. On the other hand, the tides raised on Io by Jupiter profoundly impact the evolution of the inner moons. Over the course of five thousand years, Io migrates inwards by several thousand kilometre. In doing so, Europa is brought into a closer orbit as well, to retain the resonance. Similarly, the eccentricity of both Io and Europa decreases, which in turn reduces the dissipated tidal energy and -heating. With Io being in spin-orbit resonance, tidal forces due to tides on Io are not readily applied. Multiple variations of analytical expressions of tides on Io have been evaluated. The results of this thesis provide a qualtiative assessment of the evolution of the Jupiter system and of the sustainability of Io's strong volcanism. The insight gathered on the modelling of tides and their effects on spin-orbit-resonant bodies in particular will benefit future work on the evolution of moons in the Solar System as well as exosystems.Aerospace EngineeringSpace EngineeringMSc Spacefligh
Geoid anomalies due to low-viscosity zones in glacial isostatic adjustment modeling
No full textAerospace Engineerin
Tidal deformation of Europa and Phobos: Implications on their structure and history
No full textAerospace Engineerin
Sensitivity of glacial isostatic adjustment induced rotational changes to the ice-load history
No full textAerospace Engineerin
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