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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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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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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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Recent detections of the YORP effect and their further possibilities
Vraštil, Jan ; Vokrouhlický, David (advisor) ; Ďurech, Josef (referee)
Radiation forces and torques can, on a long term, modify translational and rotational motion of small asteroids and meteoroids. In this thesis I focuse on the radiation torques dubbed the Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effect. In particular, my principal goal was to analyse available photometric database of small asteroids and suggest candidate objects for which the YORP effect could be directly detected during the next few years. The structure of the thesis is as follows: (i) in the Introduction I discuss general role of radiation forces and torques in the motion of small bodies in the Solar system, (ii) next, in Section 2, I introduce observation methods for determination of the rotation state of asteroids and the way how YORP may exhibit itself in such measurements, and (iii) finally, in Section 3, I present few candidates for the YORP effect detection. Based on this selection procedure, I obtained ligthcurves of a small near-Earth asteroid (3554) Amun from February till April 2011. These observations were performed using the 65cm telescope of the Astronomical Institute of Charles University located at Ondrejov observatory. Together with available data from Amun's 2009 and 2010 oppositions, the 2011 photometry should serve for shape and pole reconstruction of this body. The YORP effect...
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Recent asteroid breakups and accretion of interplanetary dust on the Earth
Pokorný, Petr ; Šolc, Martin (referee) ; Vokrouhlický, David (advisor)
The major aim of the thesis is an analysis of an accretion of dust originating from breakup events of Emilkowalski and YC2 asterodial families. Using a numerical integrator we follow orbits of individual dust particles, some of which will result in an impact onto one of the planets in the Solar system. Employing some non-trivial transformation we compare recorded impacts onto the Earth to available dust measurements values acquired in antarctic ice-cores. We also analyse the dynamical e ffects of Poynting-Robertson e ffect and their influence on the dust particles of variable sizes.
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