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Register a new userA statistical dynamical study of meteorite impactors: a case study based on parameters derived from the Bosumtwi impact event
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The study of meteorite craters on Earth provides information about the dynamic evolution of bodies within the Solar System. Bosumtwi crater is a well studied, 10.5 km in diameter, ca. 1.07 Ma old impact structure located in Ghana. The impactor was $sim$ 1 km in diameter, an ordinary chondrite and struck the Earth with an angle between 30$^circ$ and 45$^circ$ from the horizontal. We have used a two phase backward integration to constrain the most probable parent region of the impactor. We find that the most likely source region is a high inclination object from the Middle Main Belt.
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Fireball networks are used to recover meteorites, with the context of orbits. Observations from these networks cover the bright flight, where the meteoroid is luminescent, but to recover a fallen meteorite, these observations must often be predicted forward in time to the ground to estimate an impact position. This darkflight modelling is deceptively simple, but there is hidden complexity covering the precise interactions between the meteorite and the (usually active) atmosphere. We describe the method and approach used by the Desert Fireball Network, detailing the issues we have addressed, and the impact that factors such as shape, mass and density have on the predicted fall position. We illustrate this with a case study of Murrili meteorite fall that occurred into Lake Eyre-Kati Thanda in 2015. The fall was very well observed from multiple viewpoints, and the trajectory was steep, with a low altitude endpoint, such that the darkflight was relatively short. Murrili is 1.68 kg with a typical ordinary chondrite density, but with a somewhat flattened shape compared to a sphere, such that there are discrepancies between sphere-based predictions and the actual recovery location. It is notable that even in this relatively idealised darkflight scenario, modelling using spherical shaped projectiles resulted in a significant distance between predicted fall position and recovered meteorite.
We present a statistical analysis of the distribution of large scale topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to -1.69 +- 0.02. When this distribution is studied independently for each region, we find a good correlation between the slope of the power law and the orbital erosion rate of the surface. For instance, the northern hemisphere topography is dominated by structures on the 100~m scale while the southern hemisphere topography, illuminated at perihelion, is dominated by 10~m scale terrain features. Our study suggest that the current size of a cliff is controlled not only by material cohesion but by the dominant erosional process in each region. This observation can be generalized to other comets, where we argue that primitive nuclei are characterized by the presence of large cliffs with a cumulative height power index equal to or above -1.5, while older, eroded cometary surfaces have a power index equal to or below -2.3. In effect, our model shows that a measure of the topography provides a quantitative assessment of a comets erosional history, i.e. its evolutionary age.
The presence of mean motion resonances (MMRs) complicates analysis and fitting of planetary systems observed through the radial velocity (RV) technique. MMR can allow planets to remain stable in regions of phase space where strong planet-planet interactions would otherwise destabilize the system. These stable orbits can occupy small phase space volumes, allowing MMRs to strongly constrain system parameters, but making searches for stable orbital parameters challenging. Furthermore, libration of the resonant angle and dynamical interaction between the planets introduces another, long period variation into the observed RV signal, complicating analysis of the periods of the planets in the system. We discuss this phenomenon using the example of HD 200964. By searching through parameter space and numerically integrating each proposed set of planetary parameters to test for long term stability, we find stable solutions in the 7:5 and 3:2 MMRs in addition to the originally identified 4:3 MMR. The 7:5 configuration provides the best match to the data, while the 3:2 configuration provides the most easily understood formation scenario. In reanalysis of the originally published shorter-baseline data, we find fits in both the 4:3 and 3:2 resonances, but not the 7:5. Because the time baseline of the data is less than the resonant libration period, the current best fit to the data may not reflect the actual resonant configuration. In the absence of a full sample of the longer libration period, we find that it is of paramount importance to incorporate long term stability when fitting for the systems orbital configuration.
We present an analysis of the integrated Halpha emission line profiles for the HII region population of the spiral galaxies NGC 1530, NGC 6951 and NGC 3359. We show that 70% of the line profiles show two or three Gaussian components. The relations between the Halpha luminosity and non-thermal line width for the HII regions of the three galaxies are studied and compared with the relation found taken all the HII regions of the three galaxies as a single distribution. A clearer envelope in non-thermal line width is found when only those HII regions with non-thermal line width bigger than 13kms are considered. The linear fit for the envelope is logL=36.8+2.0*log(sigma). The masses of the HII regions on the envelope using the virial theorem and the mass estimates from the Halpha luminosity are comparable, which offers evidence that the HII regions on the envelope are virialized systems, while the remaining regions, the majority, are not in virial equilibrium.
Tens of thousands of sparse-in-time lightcurves from astrometric projects are publicly available. We investigate these data and use them in the lightcurve inversion method to derive new asteroid models. By having a greater number of models with known physical properties, we can gain a better insight into the nature of individual objects and into the whole asteroid population. We use sparse photometry from selected observatories from the AstDyS database, either alone or in combination with dense lightcurves, to determine new asteroid models by the lightcurve inversion method. We present 80 new asteroid models derived from combined data sets where sparse photometry is taken from the AstDyS database and dense lightcurves are from the Uppsala Asteroid Photometric Catalogue (UAPC) and from several individual observers. For 18 asteroids, we present updated shape solutions based on new photometric data. The addition of new models increases the total number of models derived by the lightcurve inversion method to ~200. We also present a simple statistical analysis of physical properties of asteroids where we look for possible correlations between various physical parameters with an emphasis on the spin vector. We present the observed and de-biased distributions of ecliptic latitudes with respect to different size ranges of asteroids as well as a simple theoretical model of the latitude distribution and then compare its predictions with the observed distributions. From this analysis we find that the latitude distribution of small asteroids (D < 30 km) is clustered towards ecliptic poles and can be explained by the YORP thermal effect while the latitude distribution of larger asteroids (D > 60 km) exhibits an evident excess of prograde rotators, probably of primordial origin.
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