The experiences of the Apollo lunar landings revealed the danger lunar dust can pose to surrounding hardware, outposts, and orbiting spacecraft. Future lunar missions such as the Artemis program will require more information about the trajectories of ejecta blown by landers to protect orbiting spacecraft such as the Lunar Gateway. In this paper, we simulate lunar lander ejecta trajectories using the Mercury N-body integrator. We placed cones of test particles on the Moon at the North Pole, South Pole, and Equator with various ejection speeds and angles. The results show that particles ejected at speeds near the Moon's escape velocity can take from several days to weeks to re-impact the lunar surface. The time particles spend in the vicinity of the Moon varies mostly by location. Particles stay aloft after 30 days at launch speeds as low as 2.142 km/s when launched from the Equator. Number density maps and flux density maps of the particle trajectories reveal that particles launched from the South Pole are likely to impact the Lunar Gateway at its orbit near periselene at ejection speeds as low as 2.142 km/s. Particles launched from the Equator also reach the altitude of the Gateway orbit. Particles ejected from the North Pole can impact the Gateway along its orbit at ejections speeds somewhere between 2.3324 and 2.3562 km/s.

Saturn's rings consist of icy particles of various sizes ranging from millimeters to several meters. Particles may aggregate into ephemeral elongated clumps known as self-gravity wakes in regions where the surface mass density and epicyclic frequency give a Toomre critical wavelength which is much larger than the largest individual particles (Julian and Toomre 1966). Optical depth measurements at different wavelengths can be used to constrain the sizes of individual particles (Zebker et al. 1985, Marouf et al. 1983) while measurements of optical depths spanning many viewing geometries can be used to determine the properties of self-gravity wakes (Colwell et al. 2006, 2007, Hedman et al. 2007, Nicholson and Hedman 2010, Jerousek et al. 2016). Studies constraining the parameters of the assumed power-law particle size distribution have been attempted (Zebker et al. 1985, Marouf et al. 1983) but have not yet accounted for the presence of self-gravity wakes or the much larger elongated particle aggregates seen in Cassini Imaging Subsystem (ISS) images and commonly referred to as "straw". We use a multitude of Cassini stellar occultations measured by UVIS (Ultraviolet Imaging Spectrograph) and VIMS (Visual and Infrared Mapping Spectrometer) together with Cassini's RSS (Radio Science Sub System) X-band, Ka-band, and S-band radio occultations to better constrain the particle size distribution throughout Saturn's main ring system, including regions where self-gravity wakes have a significant effect on the measured optical depth of the rings.

<p>The solar system that we live in today bears only a passing resemblance to the solar system that existed 4.5 billion years ago. As our young star shed the gas nebula from which it was born, a disk of dust and rocky bodies emerged in the space between the Sun and Jupiter. Over the next hundred million years, this planetary disk evolved and gave rise to the terrestrial planets of the inner solar system. Clues left behind during this early stage of evolution can be seen in the orbital architecture of the modern planets, the cratering records of rocky bodies, and the signatures of the solar system's secular modes. </p> <p><br></p> <p>Past works in the fields of terrestrial planet accretion and solar system evolution typically do not include collisional fragmentation. While the mechanics of collisional fragmentation are well studied, the incorporation of this processes into simulations of terrestrial planet formation is computationally expensive via traditional methods. For this reason, many works elect to exclude collisional fragmentation entirely, improving computational performance but neglecting a known process that could have played a significant role in the formation of the solar system. In this dissertation, I develop a collisional fragmentation algorithm, called Fraggle, and incorporate it into the n-body symplectic integrator Swiftest SyMBA. Along with performance enhancements and modern programming practices, Swiftest SyMBA with Fraggle is a powerful tool for simulating the formation and evolution of the inner solar system. </p> <p><br></p> <p>In this dissertation, I use Swiftest SyMBA} with Fraggle to study the effect of collisional fragmentation on the accretion and orbital architecture of the terrestrial planets, as well as the cratering record of early Mars. I show that collisional fragmentation is a significant process in the early solar system that creates a spatially heterogeneous and time-dependent population of collisional debris that fluctuates as the solar system evolves. This ever-changing population results in cratering records that are unique across the inner solar system. The work presented in this dissertation highlights the need for independent cratering chronologies to be established for all rocky bodies in the solar system, as well as the need for future models of solar system accretion to include the effects of collisional fragmentation. </p> <p><br></p> <p>While the cratering records and orbits of the terrestrial planets are two means by which to study the solar system's ancient past, analysis of the evolution of the secular modes of the solar system offers a third method. A secular mode arises due to the precession of the orbit of a planet over time. Each body's orbit precesses at a specific fundamental frequency, or mode, that has the power to shape the orbital architecture of the solar system. I show that jumps in the eccentricity of Mars can trigger short-lived power sharing relationships between secular modes, resulting in periods in which the strength and fundamental frequencies of modes fluctuates. While evidence of these past jumps in Mars' eccentricity would likely not be visible today in the secular modes of the inner solar system, the work presented in this dissertation poses additional questions. In particular, questions related to other possible triggers of power sharing relationships, as well as the effects of power sharing relationships on the stability of small bodies during these periods of fluctuation, are particularly compelling.</p> <p><br></p> <p>The work presented in this dissertation contributes to the fields of numerical modeling, solar system evolution, collisional fragmentation, martian cratering, and secular modes and resonances. As a whole, it explores avenues by which we can understand the very earliest period of our solar system's history and develops a model that will allow for continued research in this field. </p>

The existence of the exact commensurability between the periods of rotation and revolution of a satellite orbiting a planet is not a rare phenomenon in the Solar system. In fact, there are several examples of such resonances with the Earth-Moon system being the most familiar example of a 1:1 (synchronous) resonance. In this report, I will discuss the questions of stability of five resonant systems (Moon – Earth, Enceladus - Saturn, Dione - Saturn, Rhea – Saturn, and Mercury – Sun (the only non – synchronous resonance among the evolved spin – orbit resonances in the Solar system). Several authors have investigated the stability of spin-orbit resonances, and, in this report, I will concentrate on the two most recent investigations. / text

Indirect searches for planets (such as radial velocity studies)show that their formation may be quite common. The planets are however too small and faint to be seen against the glare of their host stars; therefore, their direct detectionis limited to the nearest systems. Alternatively one can study planets by studying their &quot;by-product&quot; -- dust. We see raw material available for planets around young stars, anddebris dust around old stars betraying planet-induced activity. Dust has a larger surface area per unit mass compared with a large body; it can be spread over a largersolid angle, intercepting more starlight and emitting much more lightvia reprocessing. By studying dusty disks we can infer the presence of planets at larger distances.Here we present results of a survey conducted with the SpitzerSpace Telescope of debrisdisks in three open clusters. With ages of 30--100 Myrs, these clusters are old enough that the primordialdust should have accreted into planetesimals, fallen onto the star, or been blown away due to a numberof physical processes. The dust we observe must come from collisions or sublimation of larger bodies.The purpose of this study is to investigate the dustevolution in the terrestrial planet zone, analogous to the Zodiacal cloud in our Solar system. We are most sensitive to this zone becausethe peak of a 125 K black body radiation falls into the primary pass-band of our survey -- 24 micron. We investigate the fraction and amount of the infra-red excesses around intermediate- to solar-mass stars in open stellar clusterswith well defined ages. The results are analyzed in the context of disk studies at other wavelengths and ages, providing an understanding of the time-scale for diskdissipation and ultimately planet building and frequency.

Carbonaceous chondrites have an approximately solar bulk composition, with some exceptions (e.g. H), and exhibit a range of parent body alteration. Investigations of both pristine and altered chondrites yield valuable insight into the processes and conditions of the early Solar System prior to and resulting in the planets we observe today. Such insight and the dynamic models developed by astrophysicists are constrained by chemical, mineralogical, and textural characteristics of chondrite components (chondrules, refractory inclusions, metal, and matrix). This dissertation uses a variety of chondritic components to address the following: 1) what do correlations within a population of refractory inclusions reveal about early Solar System conditions; 2) what is the distribution of trace elements among chondrite components and how does this affect component formation from precursor aggregation to chondrite accretion; and 3) can metal associated with chondrules further our understanding of chondrule formation and/or deformation? The first two objectives were investigated using suite of carbonaceous Ornans-group (CO) chondrites of varying petrologic grades (Colony CO3.0, Kainsaz CO3.2, Felix CO3.3, Moss CO3.6, and Isna CO3.8). These chondrites were analyzed using several analytical techniques including: electron microprobe element mapping, a modal phase analysis algorithm, and laser ablation inductively coupled plasma mass spectrometry. Within the comprehensive dataset of refractory inclusion characteristics (area, major mineralogy, bulk major chemistry, texture, and rare Earth element (REE) patterns and abundances) there is an overwhelming lack of correlations implying that thermal processing prior to accretion was stochastic and that sorting was minimal. Only two CO chondrites were analyzed for REE abundances (Colony and Moss). While refractory inclusions exhibit the greatest enrichments in REE relative to CI, after modal recombination chondrule glass contributes most significantly to the bulk REE budget in both chondrites. The bulk mean REE patterns for both Colony and Moss are flat and approximately CI in abundance while the mean REE patterns for components are nearly flat with relative enrichments (~10x CI for both chondrule glass and refractory inclusions) or depletions (chondrule olivine) relative to CI. Lack of correlations between REE and other characteristics, nearly flat REE patterns and nearly equivalent enrichment factors relative to CI across chondrite groups, including the CO chondrites analyzed here, implies that REE were equilibrated in precursor material prior to chondrite component formation. We propose a scenario for the equilibration of REE with vapor-solid or solid-solid reactions with subsequent accretion of chondrite components. Metal-rich chondrules in Acfer 139, a carbonaceous Renazzo-group (CR) chondrite were used to address the final objective. Chemical information was obtained using electron microprobe quantitative analysis and element mapping, electron backscatter diffraction was used to analyze the crystal structure of the metal nodules, and computed tomography provided insight into the 3D relationships of the metal. Eight chondrules with abundant metal nodules, both as rims and within the chondrule interior, were analyzed in detail. Chondrule A is of particular interest as it contains three concentric metal layers. A majority of the metal nodules fall on the calculated condensation trajectory of Co/Ni in a vapor of solar composition with the interior metal nodules containing higher Ni wt% and Co wt% than the rim nodules. Twinning is evident in many of the metal nodules and could indicate a ubiquitous parent body deformation process. Chemical inhomogeneity of Ni only occurs within the metal nodules of chondrule A and implies these metal nodules were reheated to high temperatures. The combination of chemical inhomogeneity, multiple sets of twins, and other evidence of strain imply that the formation of these chondrules was not straightforward and involved multiple iterations of heating, and potentially addition of material. A plausible model of chondrule formation in the early Solar System must be able to account for this more complicated thermal and alteration history and produce the chemical and textural variety of chondrules present in the region of chondrite accretion.

Η
 παρούσα
 εργασία
 έχει
 ως
 σκοπό
 να
 διερευνήσει
 τις
 νοητικές 
παραστάσεις
 των
 μαθητών
 της
 πέμπτης (Ε’)
 Δημοτικού
 σχετικά
με τη δομή του ηλιακού συστήματος και πιο συγκεκριμένα αναφορικά με τα εξής χαρακτηριστικά του : α. το κέντρο του ηλιακού συστήματος, β. τα δομικά μέρη του ηλιακού συστήματος (αριθμός και ονόματα πλανητών), γ. τη σφαιρική μορφή των πλανητών, δ. τις σχετικές θέσεις, αποστάσεις από τον ήλιο και τα σχετικά μεγέθη των πλανητών και ε. την κίνηση των πλανητών γύρω από τον ήλιο (περιφορά) και γύρω από τον άξονά τους (περιστροφή). Μελετάται
 επίσης
 η
 επίδραση
 ενός εκπαιδευτικού προγράμματος σε σχέση με τα παραπάνω θέματα, το οποίο σχεδιάστηκε και υλοποιήθηκε σε 61 μαθητές. Γι’
 αυτό
 το
 σκοπό,
πραγματοποιήθηκαν
 ατομικές
 συνεντεύξεις, στο
στάδιο
 των pro-tests ,
ώστε
 να 
γίνει
 ανίχνευση
 των
 νοητικών
 παραστάσεων
 των
 μαθητών για
 τη δομή του ηλιακού συστήματος,
 όπου
 τα
 παιδιά
 καλούνταν
 να σχεδιάσουν το ηλιακό σύστημα όπως πίστευαν ότι είναι και έπειτα να απαντήσουν σε ορισμένα σχετικά ερωτήματα. Ακολούθησε
 η
 Διδακτική παρέμβαση (υλοποίηση των εκπαιδευτικών δραστηριοτήτων). Έπειτα
οι
μαθητές
συμμετείχαν
σε νέες ατομικές συνεντεύξεις στο
στάδιο
των
post- tests ίδιες
 σε
 περιεχόμενο 
και
 δομή με
 τις
 πρώτες,
 προκειμένου
 να
 αξιολογηθεί
 η
 επίδραση
 της
 διδασκαλίας 
στις νοητικές τους παραστάσεις. Από 
την 
ανάλυση
 των
 αποτελεσμάτων προκύπτει ότι
 οι
 αντιλήψεις των μαθητών αναφορικά με το ηλιακό σύστημα και τα βασικά χαρακτηριστικά του μετατοπίστηκαν από διαισθητικού και συνθετικού τύπου στις επιδιωκόμενες επιστημονικού τύπου σε μεγάλο ποσοστό, κάτι το οποίο καταδεικνύει την αποτελεσματικότητα της διδακτικής παρέμβασης που έλαβε χώρα. / The present research aims to elicit the conceptions of students in the fifth grade (E') of Greek primary school regarding the structure of solar system and specifically in regard to the following characteristics : a. centre of solar system, b. the structural parts of solar system (Number and names of planets), the c. shape of the planets, d. the relative positions, distances and relative sizes of the planets and e. the movement of the planets around the sun and around their axis. The effectiveness of an educational program concerning the above issues, which was designed and implemented to 61 students, individual interviews took place ( pre- tests) in order to, detect students’ initial ideas about the structure of the solar system, during which children were asked to draw the solar system and answer relative questions. The teaching intervention took place subsequently (implementation of educational activities) . Afterwards, the students participated again in individual interviews, (post – tests), which were the same in content and structure with the first interviews (pre-tests), so that the results could be comparable . The results show that the majority of students’ conceptions concerning the solar system and its basic characteristics, changed as they progressed from intuitive and synthetic models to the expected scientific model, which shows the effectiveness of the teaching intervention that took place.

The main asteroid belt spans ~2-4 AU in heliocentric distance and is sparsely populated by rocky debris. The dynamical structure of the main belt records clues to past events in solar system history. Evidence from the structure of the Kuiper belt, an icy debris belt beyond Neptune, suggests that the giant planets were born in a more compact configuration and later experienced planetesimal-driven planet migration. Giant planet migration caused both mean motion and secular resonances to sweep across the main asteroid belt, raising the eccentricity of asteroids into planet-crossing orbits and depleting the belt. I show that the present-day semimajor axis and eccentricity distributions of large main belt asteroids are consistent with excitation and depletion due to resonance sweeping during the epoch of giant planet migration. I also use an analytical model of the sweeping of the &nu;₆ secular resonance, to set limits on the migration speed of Saturn.After planet migration, dynamical chaos became the dominant loss mechanism for asteroids with diameters D>10 km in the current asteroid belt. I find that the dynamical loss history of test particles from this region is well described with a logarithmic decay law. My model suggests that the rate of impacts from large asteroids may have declined by a factor of three over the last ~3 Gy, and that the present-day impact flux of D>10 km objects on the terrestrial planets is roughly an order of magnitude less than estimates used in crater chronologies and impact hazard risk assessments.Finally, I have quantified the change in the solar wind <super>6</super>Li/<super>7</super>Li ratio due to the estimated in-fall of chondritic material and enhanced dust production during the epoch of planetesimal-driven giant planet migration. The solar photosphere is currently highly depleted in lithium relative to chondrites, and <super>6</super>Li is expected to be far less abundant in the sun than <super>7</super>Li due to the different nuclear reaction rates of the two isotopes. Evidence for a short-lived impact cataclysm that affected the entire inner solar system may be found in the composition of implanted solar wind particles in lunar regolith.

No description available.

Our current knowledge of the Solar System, with a particular emphasis on the systems of interplanetary objects, is reviewed, and the theory of meteors and the reflection of radio waves from meteoric ionization is then discussed. A description of the meteor radar is given and a method of calibrating the antenna beam is developed. The main project comprises two parts: (a) A general survey of the radar echorate for 20 major and minor meteor streams and the sporadic meteor background, conducted from Grahamstown over the period 1986 April to 1988 January, is described. Definite shower activity was observed for all of the major and some of the minor showers. (b) Based on a scheme proposed by previous workers (Morton & Jones), a method of recovering meteor radiant distributions from the distribution of echo directions is developed. We devise a technique of compensating for possible distortions of the resulting radiant maps, which may arise due to the arisotropic antenna beam. This involves a system of echo-weighting. Radiant maps which showed considerably less distortion than those of the above workers were obtained without the weighting procedure. It is concluded that, although the method in its present form introduces spurious features into the maps, the principle is sound and should eventually be refined to produce the desired compensation