200,823 research outputs found
Exploring the Kuiper Belt: Design of trajectories for long-term Kuiper Belt exploration
No full textPrevious trajectory proposals with the purpose of exploring the Kuiper Belt have been limited to identifying trajectories to fly by a single pre-selected Kuiper Belt Object (KBO). Furthermore, these proposals were often limited to high-velocity flybys that pass through the Kuiper Belt in a limited number of years, or are based on the assumption of significant and uncertain technological advances. This thesis investigates the existence of currently feasible trajectories which position a spacecraft inside the Kuiper Belt for a significantly longer period of time. The feasibility of these trajectories is based on the assumption of current technological capabilities and a launch date between the years 2025 and 2040. To model these unique trajectories the conventional MGA-1DSM trajectory model is adapted in order to optimize trajectory problems that aim to reach the Kuiper Belt. The use of powered flybys is excluded in these problems in order to reduce problem and mission complexity. Optimization of the trajectory problems was done by performing an interactive multi-objective optimization approach with four distinct objectives on a set of twenty planetary sequences. The high complexity of these problems in combination with conflicting multiple objectives was found to necessitate an iterative optimization process using the pooled results of several algorithms in order to obtain satisfactory results. The optimization algorithm performance was further enhanced using various encouragement methods. By using the established optimization method multiple routes were identified that all culminate in a long-duration flight through the Kuiper Belt. The best results were found with planetary flyby sequences VVEJS, EVEEJN, and JN. The required launch energy (C3) for these trajectories ranges from 16 km² /s² , for sequences utilizing multiple inner planet flybys, to 75.5 km²/s² , for solutions utilizing adirect Jupiter-Neptune route. The maximum onboard delta V capability required for these solutions is 400 m/s. The flight time to the inner boundary of the Kuiper Belt ranges from 14.6 to 24 years. All thesetrajectories feature a flight time through the Kuiper Belt of well over or close to 100 years. In addition, it was found that trajectories that conclude their planetary flyby sequence with a Jupiter-Neptune leg are found to be especially well suited for long-duration Kuiper Belt flight.Aerospace Engineerin
The use of enclosed plankton communities in aquatic ecotoxicology : fate effects of mercury, cadmium and selected aromatic organics in a marine model ecosystem
No full textMost investigations in ecotoxicology are carried out in the laboratory. Although laboratory experiments are indispensable and yield useful information, it is difficult if not impossible to extrapolate results of short-term laboratory tests currently in use to real field situations. The need in aquatic ecotoxicology for experiments with complex systems, more closely approximating natural conditions, led to the use of large, flexible plastic bags, isolating part of the ecosystem, and suspended in natural waters. This approach has been used here to study marine plankton communities. The general aim of the study was to develop a method which could act as an intermediate between laboratory and field, for determining fate and effects of pollutants in low concentrations.This thesis summarizes results of several experiments, reported in detail in different papers, which are partly reproduced in the Appendix.Chapter 2 summarizes the materials and methods used. During the experiments, which usually lasted 4 - 6 weeks the development of the phytoplankton, the zooplankton and the bacteria was followed (biomass and species composition), as well as several physico-chemical factors, affecting the organisms on the various trophic levels.In the first experiments (Chapter 3) it was shown that Dutch coastal plankton communities, exposed to identical experimental conditions inside simultaneously filled plastic bags (contents 1.5 m 3), developed in very similar ways. Therefore this method could be applied for toxicological research.From 1975 onwards several experiments were carried out in which mercury, cadmium and selected organic compounds (phenol, 4-chlorophenol (4CP), 2,4-dichlorophenol (DCP) an 3,4-dichloroaniline (DCA) were added as pollutants. Most experiments were carried out with Dutch coastal water. In 1979 we participated in POSER (Plankton Observations in Simultaneous Enclosures in Rosfjorden), a project carried out in a south Norwegian fjord. There the fate and effects of mercury on plankton communities in enclosures of different dimensions were studied. Chapter 4 is devoted to the fate and effects of the model pollutants in the different experiments.The fate of the selected compounds was generally in accordance with the expectations. Cadmium remained in the system and accumulated very slowly into the sediment, which collected at the bottom of the bags. DCA was not degraded, the other organic compounds were degraded in the plankton system as well as in laboratory die-away tests. Some differences were, however, sometimes found between laboratory and semi-field experiments. Sometimes phenol and 4CP were degraded more slowly in the plankton community than in the simultaileous die-away tests, carried out using water from the enclosures. This difference was probably caused by factors working on the ecosystem level, such as competition between different bacteria for substrate and inorganic nutrients and competition between bacteria and phytoplankton for inorganic nutrients.This finding is of practical importance for the extrapolation of results of laboratory degradation tests to the field. Laboratory tests are often performed in the dark so that competition between bacteria and algae for nutrients is generally absent. Moreover nutrients are often added in large amounts to laboratory cultures. For this reason laboratory tests could easily overestimate the degradation rate in oligotrophic environments, such as most seas and oceans during a large part of the year.The fate of mercury in the modelecosystems was also unexpected. After addition of mercury(II) chloride to the systems concentrations decreased in the water and increased in 'the sediment and methylation of mercury was also found. A large part of the added mercury however, was lost to the atmosphere, probably as volatile metallic mercury.Another important result was the indication in one experiment that toxic and stable intermediates were formed during the degradation of 4CP and DCP. In most cases biodegradation tests and toxicity tests are carried out separately. In the model ecosystem fate and effects were studied simultaneously. this also appeared to be important in the case of 5-nitrofuroicacid-2, which lost both the nitrogroup and its toxicity within one day after addition to the enclosures, probably as a result of exposure to light.In most experiments effects on the enclosed plankton community could be shown after the addition of the model pollutants. Concentrations causing these effects were relatively low as compared with results of laboratory toxicity tests. Apart from this sensitivity of the test system, it is important that it appeared to be possible to experiment with various organisms on a single trophic level, as well as with different trophic levels in one system. Addition of contaminants led to effects on these interactions on, or between trophic levels.In many cases differences were found in the species composition of the plankton community between controls and contaminated systems. Changes in the relative abundance of organisms on different trophic levels were also found.. These changes may be important in field situations, because small changes, such as the disappearance or the inhibition of one species, can cause large changes in the ecosystem by complex interactions.Because mercury, cadmium, 4CP and DCP were used in the same concentrations in different experiments, information on the reproducibility of the experimental results was generated. This information is given in Chapter 5. Notwithstanding the fact that the starting conditions differed very much between experiments, it can be concluded that the toxicological results, i.e. fate of the added compounds and the concentrations having effects, are quite reproducible. The intensity of the effects depended very much on the situation in the plankton community.Chapter 6 is devoted to the possibilities for extrapolation of the results to field situations. Information from the experiments described here and from the literature suggest that the development of a plankton community inside a plastic bag, is qualitatively similar to that of the "free" community at least for periods of up to 4 weeks. With respect to the effects found, it was shown that mercury had similar effects on plankton communities enclosed at different locations (Canada, Scotland, Norway, The Netherlands). These results indicate that results obtained with the model plankton systems can be extrapolated to other sea areas. On the other hand this simple method provides just a first step, and the model systems must be seen as an intermediate between laboratory and field situations. The model system is less complex than the field situation. Even if this less complex system is investigated in a relatively simple way, as was done in this study, concentrations showing effects are among the lowest reported in the literature.In Chapter 7 some remarks are made on the optimal set-up of ecotoxicological experiments using enclosures. For ecotoxicological experiments, excluding fish or other larger carnivores, bags containing 1 - 2 m 3appear to be sufficiently large in relatively eutrophic waters, such as Dutch coastal waters. In more oligotrophic environments enclosures with a contents of approximately 10 m 3are preferred to enable larger samples to be taken. The optimal duration of an experiment is probably 4 - 6 weeks, because the enclosed community diverges more and more from the natural situation with time, making extrapolation of results to field situations more questionable.The enclosure method can be applied to at least two field of ecotoxicological problems : to assess the impact of specific dumping events and other environmental problems, and to validate laboratory toxicity and biodegradation tests
Different Roads to Liberalisation: Scenarios for a Moroccan Case Study of the Euro-Mediterranean Association Agreements. CEPS ENARPRI Working Papers No. 9, 1 October 2004
No full textAlthough the Euro-Mediterranean Partnership (EMP) in spirit aims at fostering economic growth and stability at the southern periphery of the EU, the contents of the trade agreements reflect the more narrow economic interests of specific, southern EU member states (dell’Aquila & Kuiper, 2003). Key characteristics of the Euro-Mediterranean Association Agreements (EMAAs) are an asymmetric focus on liberalising trade in the manufactured goods of the MPCs, while maintaining trade barriers on agricultural products. Several studies have quantified the expected impact of the proposed Mediterranean free trade area. A review of recent studies indicated that several characteristic features of the MPCs and the EMAAs are missing in existing analyses (Kuiper, 2004). This paper therefore focuses on identifying scenarios for further research that reflect key policy and research issues identified in an earlier study (dell’Aquila and Kuiper, 2003), while accounting for the gaps in existing analyses as identified in Kuiper (2004). Although limited to analysing the specific case of Morocco, the scenarios defined in this paper refer to issues that are relevant for all Mediterranean partner countries
DLR Advanced Study Group: KUBE² - Analysis about the possibilities of Kuiper Belt Exploitation and Exploration
No full textThe Largest Kuiper Belt Objects
No full textWhile for the first decade of the study of the Kuiper belt, a gap existed between the sizes of the relatively small and faint Kuiper belt objects (KBOs) that were being studied and the largest known KBO. Pluto, recent years have seen that gap filled and the maximum size even expanded. These large KBOs occupy all dynamical classes of the Kuiper belt with the exception of the cold classical population, and one large object, Sedna, is the first member of a new more distant population beyond the Kuiper belt. Like Pluto, most of the large KBOs are sufficiently bright for detailed physical study, and, like Pluto, most of the large KBOs have unique dynamical and physical histories that can be gleaned from these observations. The four largest known KBOs contain surfaces dominated in methane, but the details of the surface characteristics differ on each body. One large KBO is the parent body of a giant impact that has strewn multiple fragments throughout the Kuiper belt. The large KBOs have a significantly larger satellite fraction than the remainder of the Kuiper belt, including the only known multiple satellite systems and the relatively smallest satellites known. Based on the completeness of the current survey, it appears that approximately three more KBOs of the same size range likely still await discovery, but that tens to hundreds more exist in the more distant region where Sedna currently resides
OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt
No full textWe investigate different conditions, including the orbital and size-frequency distribution (SFD) of the early Kuiper Belt, that can trigger catastrophic planetesimal destruction. The goal of this study is to test if there is evidence for collisional grinding in the Kuiper Belt that has occurred since its formation. This analysis has important implications for whether the present-day SFD of the cold classical trans-Neptunian objects (TNOs) is a result of collisional equilibrium or if it reflects the primordial stage of planetesimal accretion. As an input to our modeling, we use the most up-to-date debiased OSSOS++ ensemble sample of the TNO population and orbital model based on the present-day architecture of the Kuiper Belt. We calculate the specific impact energies between impactor-target pairs from different TNO groups and compare our computed energies to catastrophic disruption results from smoothed particle hydrodynamics simulations. We explore different scenarios by considering different total primordial Kuiper Belt masses and power slopes of the SFD and allowing collisions to take place over different timescales. The collisional evolution of the Kuiper Belt is a strong function of the unknown initial mass in the trans-Neptunian region, where collisional grinding of planetesimals requires a total primordial Kuiper Belt mass of M > 5 M ⊕, collision speeds as high as 3 km s−1, and collisions over at least 0.5 Gyr. We conclude that presently, most of the collisions in the trans-Neptunian region are in the cratering rather than disruption regime. Given the low collision rates among the cold classical Kuiper Belt objects, their SFD most likely represents the primordial planetesimal accretion. © 2022. The Author(s). Published by the American Astronomical Society.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
POPULATION OF THE SCATTERED KUIPER BELT1
No full textWe present the discovery of three new scattered Kuiper Belt objects (SKBOs) from a wide-field survey of the ecliptic. This continuing survey has to date covered 20.2 deg2 to a limiting red magnitude of 23.6. We combine the data from this new survey with an existing survey conducted at the University of Hawaii 2.2 m telescope to constrain the number and mass of the SKBOs. The SKBOs are characterized by large eccentricities, perihelia near 35 AU, and semimajor axes greater than 50 AU. Using a maximum likelihood model, we estimate the total number of SKBOs larger than 100 km in diameter to be (1 j errors) and the total mass of11.9 4N = (3.1) # 1021.3 SKBOs to be M%, demonstrating that the SKBOs are similar in number and mass to the Kuiper BeltM » 0.05 inside 50 AU. Subject headings: comets: general — Kuiper Belt, Oort Cloud — solar system: formatio
Geology of the Kuiper quadrangle (H06), Mercury
No full textThe Kuiper quadrangle (H06) is located at the equatorial zone of Mercury and encompasses the area between 288°E–360°E and 22.5°N–22.5°S. Using the NASA MESSENGER data, we compiled a geological map of the quadrangle at a 1:3,000,000 scale. The mapping was mainly based on photo-interpretation of an MDIS (Mercury Dual Imaging System) monochrome 166 m/pixel basemap. Additional datasets were also considered: stereo-DTM of the region, mosaics with high-incidence illumination, and the MDIS global color mosaic. The map shows that the quadrangle is characterized by the prevalence of crater materials which are distinguished into three classes based on their degradation degree. Different plain units were also identified and classified on the basis of their density of cratering. Several structures, mainly represented by contractional faults, were mapped in all quadrangle areas. The map represents the first complete geologic survey of H06 at this scale and provides a highly detailed analysis of the Kuiper quadrangle’s surface geology
THE KUIPER BELT AND ITS PRIMORDIAL SCULPTING
No full textAbstract. We discuss the structure of the Kuiper belt as it can be inferred from the first decade of observations. In particular, we focus on its most intriguing properties – the mass deficit, inclination distribution, the apparent existence of an outer edge and of a correlation among inclinations, colours and sizes – which clearly show that the belt has lost its pristine structure of a dynamically cold protoplanetary disk. Understanding how the Kuiper belt acquired its present structure will provide insight into the formation of the outer planetary system and on its early evolution. We outline a scenario of primordial sculpting – issued from a combination of mechanisms proposed by various authors – that seems to explain most of the observed properties of the Kuiper belt. Several aspects are not yet totally clear. But, for the first time, we have a view – if not of the detailed sculpture – at least of its rough cast. 1
Thermal evolution and differentiation of Edgeworth-Kuiper belt objects
No full textThe region beyond Neptune's orbit is populated by numerous bodies with semimajor axes from 31 to 48 AU. This region, known as the Kuiper belt, should contain primitive bodies, perhaps among the most primitive objects in the solar system. These bodies could be remnants of the solar system formation. They seem to be dark, volatile-rich objects showing a strong relationship with comets: the Kuiper belt is probably the source of most short-period comets and Centaurs. The Kuiper belt objects (KBOs) could still contain ices and organic compounds in unaltered proportions with respect to those of their formation. Thermal models of bodies moving in Kuiper belt orbits have been developed to follow their evolution and differentiation and to better understand the relations between them and the short-period comets and Centaurs. In these models, we assume that KBOs are porous bodies composed of ices and dust. The solar energy is very low, between 30 and 50 AU, and radiogenic heating becomes a nonnegligible source of energy for differentiation. The radioactive elements, if they exist in sufficient quantity, may modify the original composition of cometary nuclei. In the models reported here, we have assumed that the radiogenic elements stored in the refractory component are K-40, Th-232,U-235, and U-238, in meteoritic proportions. In some models, we have also included the short-lived radio nuclide Al-26. The aim of this work is to see how an undifferentiated Kuiper belt body can change its internal structure under the combined effect of radiogenic heating and solar irradiation. Moderate heating can permit the sublimation of the most volatile ices both from the interior and from the surface, depending on the dominant heat source. The main result is that Kuiper belt objects can be strongly volatile depleted. From the surface down to several hundred meters below the surface, the most volatile ices (like CO) can be completely absent
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