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Rotational dynamics of asteroids affected by thermal emission from topographic features
Ševeček, Pavel ; Brož, Miroslav (advisor) ; Henych, Tomáš (referee)
Infrared radiation emitted from an asteroid surface causes a torque that can significantly affect rotational state of the asteroid. The influence of small topographic features on this phenomenon, called the YORP effect, hasn't been studied yet in detail. In this work, we show that lateral heat diffusion in surface features of suitable sizes leads to the emergence of a local YORP effect which magnitude is comparable to the YORP effect due to the global shape. We solve a three- dimensional heat diffusion equation in a boulder and its surroundings by the finite element method using the FreeFem++ code. The contribution to the total torque is then inferred from the com- puted temperature distribution. We compare the torque for various boulder shapes and material properties. For an idealized boulder our result is consistent with an existing one-dimensional model. Topographic features may cause a spherical asteroid of radius 1 km on a circular orbit at 2.5 AU to undergo a rotational acceleration of about (2.2 ± 1.1) · 10−9 rad/day2 , which corresponds to the spin-up timescale of the order τ = (32 ± 16) Myr. We estimated a size distribution of boulders based on close-up images of (25143) Itokawa surface. Finally, we realized that topographic features of Itokawa can induce a rotational acceleration of the order 10−7...
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Interactions of migrating giant planets and small solar-system bodies
Chrenko, Ondřej ; Brož, Miroslav (advisor) ; Wünsch, Richard (referee)
Changes of semimajor axes of giant planets, which took place 4 billion years ago and evolved the Solar System towards its present state, affected various populations of minor Solar-System bodies. One of these populations was a group of dynamically stable asteroids in the 2:1 mean-motion resonance with Jupiter which reside in two islands of the phase space, denoted A and B, and exhibit lifetimes comparable to the age of the Solar System. The origin of stable asteroids has not been explained so far. Our main goal is to create a viable hypothesis of their origin. We update the resonant population and its physical properties on the basis of up-to-date observational data. Using an N-body model with seven giant planets and the Yarkovsky effect included, we demonstrate that the depletion of island A is faster compared to island B. We then investigate: (i) survivability of primordial resonant asteroids and (ii) capture of the population during planetary migration, using a recently described scenario with an escaping fifth giant planet and a jumping-Jupiter instability. We employ simulations with prescribed migration, smooth late migration and we statistically evaluate the results using dynamical maps. We also model collisions during the last 4 billion years. We conclude that the long-lived group was created by a...
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Asteroid families and their relation to planetary migration
Rozehnal, Jakub ; Brož, Miroslav (advisor) ; Vokrouhlický, David (referee)
In this thesis, we study how the planetary migration affects asteroid families. We identify the families among the Trojans of Jupiter by analysing their properties in the space of resonant elements, the size-frequency distribution and the colour indices. The previously reported number of families (10) seems to be overestimated, our analysis indicates that there is only one collisional family among Trojans with the parent-body size DPB > 100 km. We also performed a simulation of the long-term orbital evolution of the Trojan families. We used a modified version of the SWIFT symplectic integrator where the migration is set analytically. We found that the families are unstable even in the late stages of the migration, when Jupiter and Saturn recede from their mutual 1:2 resonance. Hence, the families observed today must have been created after the planetary migration ended. In the last part of the work, we study a formation of asteroid families in the Main Belt during the Late Heavy Bombardement. We simulate perturbations induced by migrating planets in the "jumping Jupiter" scenario (Morbidelli et al., 2010) and we conclude that big families (DPB > 200 km) created during the bombardement should be observable today.
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The application of the LSST in the physics of the small solar-system bodies
Sváda, Petr ; Brož, Miroslav (advisor) ; Wolf, Marek (referee)
This thesis is devoted to the description of the Large Synoptics Survey Telescope (LSST) and its use in the physics of small solar-system bodies. Based on the telescope optics parameters and the theory of signal and noise we calculate limiting magnitude of the LSST (24,9 0,4) mag (in the V band). This value, together with data from MPC and WISE databases, serve as an input parameter for the calculation of the minimum diameter ( ) m of a main-belt asteroid, that LSST will be able to observe. We also estimated that (160 ± 118) million asteroids could be observable by the LSST. Taking into account the planned observational strategy and cadence, we calculated that a sufficiently bright asteroid will be observed approximately 370 times. Finally, the possible applications of the LSST are discussed: e. g. a development of collisional models, explanation of orbital and rotational dynamics of sub-kilometer objects.
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Origin of asteroids in the 2:1 mean-motion resonance with Jupiter
Chrenko, Ondřej ; Brož, Miroslav (advisor) ; Hanuš, Josef (referee)
Asteroids located in the 2:1 mean-motion resonance with Jupiter are classified as stable (called Zhongguos), marginally stable (called Griquas) and unstable (called Zulus) according to their dynamical lifetime. The stable asteroids reside in two separate stable islands in the pseudo-proper element space. In this thesis, we update the resonant population on the basis of up-to-date observational data and we determine orbital and physical properties of the resonant population. Using collisional models, we demonstrate that the observed Zhongguos and Griquas might be up to 4 Gyr old, thus their origin might be related to the planetary migration. Performing dynamical N-body simulations, we test two hypotheses of the origin of the long-lived population: the primordial population scenario, and the asteroidal capture scenario. Our results imply that the resonant population is not primordial but it was rather formed by the asteroids captured from an asteroidal family located in outer main belt.
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Inner belt asteroids in the spin-orbital resonance
Vraštil, Jan ; Vokrouhlický, David (advisor) ; Brož, Miroslav (referee)
Context: Slivan (2002) determined spin state of ten asteroids in the Koronis family. Surprisingly, all four asteroids with prograde sense of rotation were shown to have spin axes nearly parallel in the inertial space. All asteroids with retrograde sense of rotation had large obliquities and rotation periods either short or long. It was shown that Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect can explain all these peculiar facts. In particular, it drives spin axes of the prograde rotators to be captured in a secular spin-orbital resonance known as Cassini state 2. Vokrouhlický et al. (2002) dubbed these configurations "Slivan states". Aims: A question arises whether Slivan states could exist also in other regions of the main asteroid belt, in particular its inner part, where observations are most easily obtained. Here, however, dynamical difficulties arise due to convergence of the proper frequency s and the planetary frequency s6. We investigate possibilities of a long-term stable capture in the Slivan state in the inner part of the main belt. Method: We used SWIFT integrator to determine orbital evolution of selected asteroids in the inner part of the main belt. In the case of 20 Massalia, we observed the asteroid in 2011, and used these new data to help better solve the rotation state using the...
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Collisional evolution of the Main Asteroid Belt over 4 billion years
Cibulková, Helena ; Brož, Miroslav (advisor) ; Ďurech, Josef (referee)
In this work, we constructed a new model for the collisional evolution of the Main Asteroid Belt. Our goals are to test the scaling law from the work of Benz & Asphaug (1999) and ascertain if it can be used for the whole belt. We want to find initial size-frequency distributions (SFDs) for the considered six parts of the belt, and to verify if the number of asteroid families created during the simulation matches the number of observed families as well. We used new observational data from the WISE satellite (Masiero et al., 2011) to construct the observed SFDs. We simulated mutual collisions of asteroids with a modified Boulder code (Morbidelli et al., 2009), in which the results of hydrodynamic (SPH) simulations from the work of Durda et al. (2007) are included. Because material characteris- tics can affect breakups, we created two models - for monolithic asteroids and for rubble-piles (Benavidez et al., 2012). The results for monolithic and rubble- -pile asteroids are comparable and in both cases the number of created families is, within uncertainties, consistent with the observations. A disagreement of the SFDs for a limited size range D 1 to 5 km a is a good motivation to conduct new SPH simulations with relatively small targets. 1
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Velké pozdní bombardování v různých místech sluneční soustavy
Zajaček, Michal ; Brož, Miroslav (advisor) ; Ďurech, Josef (referee)
In this work, we study the Late Heavy Bombardment (LHB) in the Solar System which took place from 4.1 to 3.8 billion years ago, and represents a period of intense collisions whose traces are observed on the Moon and other bodies mainly in the form of craters or impact melts. The first part of the thesis is a review on the LHB with the focus on observational evidence and recent dynamical models. In the second part, we test a particular dynamical model of the LHB using the observed cratering records on various Solar-System bodies, which was not done previously to such an extent. For this purpose, we use the symplectic integrator SyMBA, the collisional code Boulder, and various projectile-crater scaling laws. We discuss the sources of uncertainties of the observations as well as that of the models. Furthermore, we use our results to constrain the size-frequency distribution of the primordial cometary population.
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Propagating star formation
Dinnbier, František ; Wünsch, Richard (advisor) ; Brož, Miroslav (referee) ; Naab, Thorsten (referee)
Massive stars are powerful energetic sources shaping their surrounding interstellar medium, which is often swept up into a cold dense shell. If the shell fragments and forms a new generation of massive stars, the stars may form new shells, and this sequence repeats recursively leading to propagating star formation. Using three dimensional hydrodynamic simulations, we investigate fragmentation of the shell in order to estimate masses of stars formed in the shell. We develop a new numerical method to calculate the gravitational potential, which enables us to approximate a part of the shell with a plane-parallel layer. Our main results are as follows. Firstly, we compare our numerical calculations to several analytical theories for shell fragmentation, constrain the parameter space of their validity, and discuss the origin of their limitations. Secondly, we report a new qualita- tively different mode of fragmentation - the coalescence driven collapse. While layers with low pressure confinement form monolithically collapsing fragments, layers with high pressure confinement firstly break into stable fragments, which subsequently coalesce. And thirdly, we study whether layers tend to self-organise and form regular patterns as was suggested in literature, and we find no evidence for this conjecture. Based on our...
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Rovnice vedení tepla ve fyzice planetek a meteoroidů
Pohl, Leoš ; Brož, Miroslav (advisor) ; Vokrouhlický, David (referee)
Non-gravitational forces caused by thermal emission of photons can significantly change orbits and spin states of asteroids in the long term. A solution of the Heat Conduction Equation (HCE) in an asteroid is necessary to evaluate the forces. Finite Difference Methods (FDMs) are implemented in a Fortran numerical HCE solver to calculate a temperature distribution within a system of 1-dimensional slabs which approximate the asteroid. We compare the methods w.r.t. convergence, accuracy and computational efficiency. The numerical results are compared with a simplified steady-state analytical solution. We calculate the non-gravitational accelerations and resulting semimajor axis drift from the numerical results. The implemented FDMs are shown to be convergent with denser grids and the best method has been selected. The analytical solution provides a good first-guess estimate of the temperature amplitude. The drift in semimajor axis of the tested asteroids, which is due to the non-gravitational forces, is in order-of-magnitude agreement with more accurate models and observational data.
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