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Leliwa-Kopystynski J.,University of Warsaw | Wodarczyk I.,Chorzow Astronomical Observatory | Burchell M.J.,University of Kent
Icarus | Year: 2016

A model of impact disruption of the bodies with sizes from the laboratory scale to that of an order of 100km is developed. On the lowermost end of the target size the model is based on the numerous laboratory data related to the mass-velocity distribution of the impact produced fragments. On the minor-planets scale the model is supported by the data related to the largest observed craters on small icy satellites and on some asteroids (Leliwa-Kopystynski, J., Burchell, M.J., Lowen, D. [2008]. Icarus 195, 817-826). The model takes into account the target disruption and the dispersion of the impact produced fragments against the intermolecular forces acting on the surfaces of the contacts of the fragments and against self-gravitation of the target. The head-on collisions of non-rotating and non-porous targets and impactors are considered. The impactor delivers kinetic energy but its mass is neglected in comparison to mass of the target. For this simple case the analytical formulae for specific disruption energy as well as for specific energy of formation of the largest craters are found. They depend on a set of parameters. Of these the most important (i.e. with the greatest influence on the final result) are three rather weakly known parameters. They are: (i) The exponent γ in the distribution function of the fragments. (ii) The characteristic velocity v0 that appears in the velocity distribution of the ejected fragments. (iii) The exponent β in the mass-velocity distribution. The influence of the choice of the numerical values of these parameters on the final results has been studied. Another group of parameters contains the relevant material data. They are: (a) The energy σ of breaking of the intermolecular bonds of the target material per unit of the fragment surface and (b) the density ρ of the target. According to our calculations the transition between the strength regime and the gravitational regime is in the range of the target radius from ~0.4km to ~4km. This estimate holds within a large range of parameters.An application of the results for impact cratering and/or for disruption of satellites and asteroids requires data concerning the impactor energy. We have considered rocky-rocky impacts (an asteroid on an asteroid) and icy-icy impacts (a satellite impacted by a comet). Hypothetical impacts onto some particular asteroids and satellites are discussed as examples. © 2016 Elsevier Inc. Source

Wlodarczyk I.,Chorzow Astronomical Observatory
Bulgarian Astronomical Journal | Year: 2015

Third of the most interesting potentially dangerous asteroids, after (99942) Apophis and (101955) Bennu, is 2009 FD. We computed impact solutions of the asteroid 2009 FD based on its 296 optical observations from 2009 February 24.36493 UTC to 2014 April 02.15110 UTC, and 1 radar observation from 2014 April 07 20:21:00 UTC. We used the freely available OrbFit Software Package and studied the orbit of 2009 FD forward in the future searching for close approaches with the Earth and for possible impacts up to 2201. Possible impact solutions were computed using the JPL DE405 planetary and lunar ephemerides taking into account the different A2 non-gravitational parameter in the motion of the asteroid 2009 FD. We computed possible impacts in 2185, 2186, 2191, 2192, 2194, 2196 and 2198. They are possible only with the non-gravitational parameter, A2 in the range (-46.0, 0)×10−15au/d2, with the gap between (-25.0, -11.0)×10−15au/d2. It denotes that if A2 is greater than +0.0×10−15au/d2, or smaller than –46.0×10−15au/d2 than impacts with the Earth, are excluded. They are possible with the non-gravitational parameter, A2<=0. It implies that impacts are possible if 2009 FD rotates in retrograde direction. © 2015, Bulgarian Astronomical Journal. All rights reserved. Source

Cernis K.,Vilnius University | Zdanavicius J.,Vilnius University | Wlodarczyk I.,Chorzow Astronomical Observatory | Stonkute E.,Vilnius University
Baltic Astronomy | Year: 2012

A project devoted to astrometric and photometric observations of asteroids at the Mole̊tai Observatory is described. One of its most important results is the discovery of the asteroid 2010 BT3 belonging to the Amor group of the near-Earth objects. The results of astrometrie and photometric observations of the asteroid are presented. The brightness variations of the asteroid are found to be about 0.2 mag in R. The orbit of the asteroid was computed from 96 observations. This orbit, combined with the apparent brightness, gives the absolute magnitude 21.34 mag and the diameter between 160 m and 360 m, taking albedos of S-type and C-type asteroids, respectively. Source

Wlodarczyk I.,Chorzow Astronomical Observatory
Acta Astronomica | Year: 2015

The asteroid (410777) 2009 FD is placed at the top of the JPL NASA Sentry Risk Table. We show that the predicted probability of the potential impact of the asteroid (410777) 2009 FD in fact depends on (i): used methods of selection and weighing of observational data, (ii): adopted dynamical model with included non-gravitational effects in the motion of asteroid based on cometary approach, and considerably weaker depends on (iii): the used model of the Solar System with different number of massive asteroids as potential perturbers. We computed impact solutions of the asteroid (410777) 2009 FD based on its 296 optical observations from February 24, 2009 to April 02, 2014 and one radar observation from April 07, 2014. We used the freely available ORBFIT Software Package and studied the future evolution of the orbit of (410777) 2009 FD searching for close approaches with the Earth and for the possible impacts up to the year 2200. According to our study the impacts are possible in the years: 2185, 2186, 2190, 2191, 2192, 2194, 2196, and 2198, provided the non-gravitational parameter A2 in the range of (-46.0,+3.0)×10-15 a.u./d2, with the gap between (-25.0,-11.0)×10-15 a.u./d2. Source

Cernis K.,Vilnius University | Wlodarczyk I.,Chorzow Astronomical Observatory | Zdanavicius J.,Vilnius University
Baltic Astronomy | Year: 2014

The paper presents statistics of the asteroids observed and discovered at the Molėtai Observatory, Lithuania in 2000-2004 within the project for astrometric observations of the near-Earth objects (NEOs), the main belt asteroids and comets. CCD observations of asteroids were obtained with the 35/51 cm Maksutov-type meniscus telescope and the 1.65 m Ritchey-Chretien reflector. In the Minor Planet Circulars and the Minor Planet Electronic Circulars (2000-2004) we published 6629 astrometric positions of 1114 asteroids. Among them 78 were newly discovered asteroids at Molėtai, a few NEOs were found by our team independently. For the 67 asteroids discovered at Molėtai the precise orbits were calculated. Because of small number of observations, a few asteroids have low-precision orbits and some asteroids have been lost. For seven objects we present their ephemerides for 2015. Source

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