Browsing by Subject "meteorites, meteors, meteoroids"

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  • Chrbolková, Kateřina; Brunetto, Rosario; Ďurech, Josef; Kohout, Tomáš; Mizohata, Kenichiro; Malý, Petr; Dědič, Václav; Lantz, Cateline; Penttilä, Antti; Trojánek, František; Maturilli, Alessandro (2021)
    Context. Space weathering is a process that changes the surface of airless planetary bodies. Prime space weathering agents are solar wind irradiation and micrometeoroid bombardment. These processes alter planetary reflectance spectra and often modify their compositional diagnostic features. Aims. In this work we focused on simulating and comparing the spectral changes caused by solar wind irradiation and by micrometeoroid bombardment to gain a better understanding of these individual space weathering processes. Methods. We used olivine and pyroxene pellets as proxies for planetary materials. To simulate solar wind irradiation we used hydrogen, helium, and argon ions with energies from 5 to 40 keV and fluences of up to 10(18) particles cm(-2). To simulate micrometeoroid bombardment we used individual femtosecond laser pulses. We analysed the corresponding evolution of different spectral parameters, which we determined by applying the Modified Gaussian Model, and we also conducted principal component analysis. Results. The original mineralogy of the surface influences the spectral evolution more than the weathering agent, as seen from the diverse evolution of the spectral slope of olivine and pyroxene upon irradiation. The spectral slope changes seen in olivine are consistent with observations of A-type asteroids, while the moderate to no slope changes observed in pyroxene are consistent with asteroid (4) Vesta. We also observed some differences in the spectral effects induced by the two weathering agents. Ions simulating solar wind have a smaller influence on longer wavelengths of the spectra than laser irradiation simulating micrometeoroid impacts. This is most likely due to the different penetration depths of ions and laser pulses. Our results suggest that in some instances it might be possible to distinguish between the contributions of the two agents on a weathered surface.
  • Ye, Quanzhi; Granvik, Mikael (2019)
    The under-abundance of asteroids on orbits with small perihelion distances suggests that thermally driven disruption may be an important process in the removal of rocky bodies in the solar system. Here we report our study of how the debris streams arise from possible thermally driven disruptions in the near-Sun region. We calculate that a small body with a diameter greater than or similar to 0.5 km can produce a sufficient amount of material to allow the detection of the debris at the Earth as meteor showers, and that bodies at such sizes thermally disrupt every similar to 2 kyr. We also find that objects from the inner parts of the asteroid belt are more likely to become Sun-approachers than those from the outer parts. We simulate the formation and evolution of the debris streams produced from a set of synthetic disrupting asteroids drawn from Granvik et al.'s near-Earth object population model, and find that they evolve 10-70 times faster than streams produced at ordinary solar distances. We compare the simulation results to a catalog of known meteor showers on Sun-approaching orbits. We show that there is a clear overabundance of Sun-approaching meteor showers, which is best explained by a combining effect of comet contamination and an extended disintegration phase that lasts up to a few thousand years. We suggest that a few asteroid-like Sun-approaching objects that brighten significantly at their perihelion passages could, in fact, be disrupting asteroids. An extended period of thermal disruption may also explain the widespread detection of transiting debris in exoplanetary systems.
  • Moilanen, Jarmo; Gritsevich, Maria; Lyytinen, Esko (2021)
    When an object enters the atmosphere it may be detected as a meteor. A bright meteor, called a fireball, may be a sign of a meteorite fall. Instrumentally observed meteorite falls provide unique opportunities to recover and analyse unweathered planetary samples supplemented with the knowledge on the Solar system orbit they had. To recover a meteorite from a fireball event, it is essential that recovery teams can be directed to a well-defined search area. Until recently, simulations showing the realistic mapping of a strewn field were difficult, in particular due to the large number of unknowns not directly retrieved from the fireball observations. These unknowns include the number of fragments and their aerodynamic properties, for which the masses of the fragments need to be assumed in a traditional approach. Here, we describe a new Monte Carlo model, which has already successfully assisted in several meteorite recoveries. The model is the first of its kind as it provides an adequate representation of the processes occurring during the luminous trajectory coupled together with the dark flight. In particular, the model comprises a novel approach to fragmentation modelling that leads to a realistic fragment mass distribution on the ground. We present strewn field simulations for the well-documented Kosice and Neuschwanstein meteorite falls, which demonstrate good matches to the observations. We foresee that our model can be used to revise the flux of extra-terrestrial matter onto the Earth, as it provides a possibility of estimating the terminal mass of meteorite fragments reaching the ground.
  • Kohout, T.; Petrova, E.; Yakovlev, G. A.; Grokhovsky, V.; Penttilä, A.; Maturilli, A.; Moreau, J-G; Berzin, S.; Wasiljeff, J.; Danilenko, I. A.; Zamyatin, D. A.; Muftakhetdinova, R. F.; Heikkilä, M. (2020)
    Context. Shock-induced changes in ordinary chondrite meteorites related to impacts or planetary collisions are known to be capable of altering their optical properties. Thus, one can hypothesize that a significant portion of the ordinary chondrite material may be hidden within the observed dark C/X asteroid population. Aims. The exact pressure-temperature conditions of the shock-induced darkening are not well constrained. Thus, we experimentally investigate the gradual changes in the chondrite material optical properties as a function of the shock pressure. Methods. A spherical shock experiment with Chelyabinsk LL5 was performed in order to study the changes in its optical properties. The spherical shock experiment geometry allows for a gradual increase of shock pressure from similar to 15 GPa at a rim toward hundreds of gigapascals in the center. Results. Four distinct zones were observed with an increasing shock load. The optical changes are minimal up to similar to 50 GPa. In the region of similar to 50-60 GPa, shock darkening occurs due to the troilite melt infusion into silicates. This process abruptly ceases at pressures of similar to 60 GPa due to an onset of silicate melting. At pressures higher than similar to 150 GPa, recrystallization occurs and is associated with a second-stage shock darkening due to fine troilite-metal eutectic grains. The shock darkening affects the ultraviolet, visible, and near-infrared region while changes to the MIR spectrum are minimal. Conclusions. Shock darkening is caused by two distinct mechanisms with characteristic pressure regions, which are separated by an interval where the darkening ceases. This implies a reduced amount of shock-darkened material produced during the asteroid collisions.
  • Toliou, Athanasia; Granvik, Mikael; Tsirvoulis, Georgios (2021)
    The observed near-Earth asteroid (NEA) population contains very few objects with small perihelion distances, say, q less than or similar to 0.2 au. NEAs that currently have orbits with larger q might be hiding a past evolution during which they have approached closer to the Sun. We present a probabilistic assessment of the minimum q that an asteroid has reached during its orbital history. At the same time, we offer an estimate of the dwell time, that is, the time q has been in a specific range. We have re-analysed orbital integrations of test asteroids from the moment they enter the near-Earth region until they either collide with a major body or are thrown out from the inner Solar system. We considered a total disruption of asteroids at certain q as a function of absolute magnitude (H). We calculated the probability that an asteroid with given orbital elements and H has reached a q smaller than a given threshold value and its respective dwell time in that range. We have constructed a look-up table that can be used to study the past orbital and thermal evolution of asteroids as well as meteorite falls and their possible parent bodies. An application to 25 meteorite falls shows that carbonaceous chondrites typically have short dwell times at small q, whereas for ordinary chondrites it ranges from 10 000 to 500 000 yr. A dearth of meteorite falls with long dwell times and small minimum q supports a supercatastrophic disruption of asteroids at small q.
  • Valiev, R. R.; Berezhnoy, A. A.; Gritsenko, I. S.; Merzlikin, B. S.; Cherepanov, Viktor N.; Kurten, Theo; Wöhler, Chrisitan (2020)
    We calculated the cross sections of photolysis of OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF molecules using quantum chemistry methods. The maximal values for photolysis cross sections of alkali metal monoxides are on the order of 10(-18) cm(2). The lifetimes of photolysis for quiet Sun at 1 astronomical unit are estimated as 2.0 x 10(5), 28, 5, 14, 2.1 x 10(5), 225, 42, 52, 2 x 10(6), 35 400, 486, and 30 400 s for OH, LiO, NaO, KO, HCl, LiCl, NaCl, KCl, HF, LiF, NaF, and KF, respectively. We performed a comparison between values of photolysis lifetimes obtained in this work and in previous studies. Based on such a comparison, our estimations of photolysis lifetimes of OH, HCl, and HF have an accuracy of about a factor of 2. We determined typical kinetic energies of main peaks of photolysis-generated metal atoms. Impact-produced LiO, NaO, KO, NaCl, and KCl molecules are destroyed in the lunar and Hermean exospheres almost completely during the first ballistic flight, while other considered molecules are more stable against destruction by photolysis.
  • Moreno-Ibanez, Manuel; Gritsevich, Maria; Trigo-Rodriguez, Josep M.; Silber, Elizabeth A. (2020)
    Meteoroids impacting the Earth atmosphere are commonly classified using the PE criterion. This criterion was introduced to support the identification of the fireball type by empirically linking its orbital origin and composition characteristics. Additionally, it is used as an indicator of the meteoroid tensile strength and its ability to penetrate the atmosphere. However, the level of classification accuracy of the PE criterion depends on the ability to constrain the value of the input data, retrieved from the fireball observation, required to derive the PE value. To overcome these uncertainties and achieve a greater classification detail, we propose a new formulation using scaling laws and dimensionless variables that groups all the input variables into two parameters that are directly obtained from the fireball observations. These two parameters, alpha and beta, represent the drag and the mass-loss rates along the luminous part of the trajectory, respectively, and are linked to the shape, strength, ablation efficiency, mineralogical nature of the projectile, and duration of the fireball. Thus, the new formulation relies on a physical basis. This work shows the mathematical equivalence between the PE criterion and the logarithm of 2 alpha beta under the same PE criterion assumptions. We demonstrate that log(2 alpha beta) offers a more general formulation that does not require any preliminary constraint on the meteor flight scenario and discuss the suitability of the new formulation for expanding the classification beyond fully disintegrating fireballs to larger impactors including meteorite-dropping fireballs. The reliability of the new formulation is validated using the Prairie Network meteor observations.
  • Moreno-Ibanez, Manuel; Silber, Elizabeth A.; Gritsevich, Maria; Trigo-Rodriguez, Josep M. (2018)
    Infrasound monitoring has proved to be effective in detection of meteor-generated shock waves. When combined with optical observations of meteors, this technique is also reliable for detecting centimeter-sized meteoroids that usually ablate at high altitudes, thus offering relevant clues that open the exploration of the meteoroid flight regimes. Since a shock wave is formed as a result of a passage of the meteoroid through the atmosphere, the knowledge of the physical parameters of the surrounding gas around the meteoroid surface can be used to determine the meteor flow regime. This study analyzes the flow regimes of a data set of 24 centimeter-sized meteoroids for which well-constrained infrasound and photometric information is available. This is the first time that the flow regimes for meteoroids in this size range are validated from observations. From our approach, the Knudsen and Reynolds numbers are calculated, and two different flow regime evaluation approaches are compared in order to validate the theoretical formulation. The results demonstrate that a combination of fluid dynamic dimensionless parameters is needed to allow a better inclusion of the local physical processes of the phenomena.