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Magorzata Królikowska Grzegorz Sitarski Andrzej M. Sotan 《Monthly notices of the Royal Astronomical Society》2009,399(4):1964-1976
The aim of this paper is to show that in the case of a low probability of asteroid collision with the Earth, the appropriate selection and weighting of the data are crucial for the impact investigation and for analysing the impact possibilities using extensive numerical simulations. By means of the Monte Carlo special method, a large number of 'clone' orbits have been generated. A full range of orbital elements in the six-dimensional parameter space, that is, in the entire confidence region allowed by the observational material, has been examined. On the basis of 1000 astrometric observations of (99942) Apophis, the best solutions for the geocentric encounter distance of 6.065 ± 0.081 R⊕ (without perturbations by asteroids) or 6.064 ± 0.095 R⊕ (including perturbations by the four largest asteroids) were derived for the close encounter with the Earth on 2029 April 13. The present uncertainties allow for special configurations ('keyholes') during this encounter that may lead to very close encounters in future approaches of Apophis. Two groups of keyholes are connected with the close encounter with the Earth in 2036 (within the minimal distance of 5.7736−5.7763 R⊕ on 2029 April 13) and 2037 (within the minimal distance of 6.3359–6.3488 R⊕ ). The nominal orbits for our most accurate models run almost exactly in the middle of these two impact keyhole groups. A very small keyhole for the impact in 2076 has been found between these groups at the minimal distance of 5.97347 R⊕ . This keyhole is close to the nominal orbit. The present observations are not sufficiently accurate to eliminate definitely the possibility of impact with the Earth in 2036 and for many years after. 相似文献
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Szutowicz Sławomira Królikowska Małgorzata Sitarski Grzegorz 《Earth, Moon, and Planets》2002,90(1-4):119-130
The role of non-gravitational forces in the evolution of orbitalmotion of C/1995 O1 (Hale–Bopp) has been investigated. Inorbital
calculations the observational material covering theperiod from April 1993 up to August 2001 was used. To model thenon-gravitational
acceleration, observed and theoretical profilesof the H2O production rates were employed. A set of forcedprecession models of a rotating cometary nucleus consistent withthe observed
spin axis orientation was fitted to positionalobservations. The non-gravitational models allowed us to constrainthe mass and
radius of the comet. The orbitalevolution of Comet Hale–Bopp was investigated over ±400 k yusing two sets of randomly varied
orbital elements wellrepresenting all positional observations in the pure gravitationalcase, as well as in the non-gravitational
case. The calculationsshowed that the comet's motion is predictable only over an interval ofa few orbital periods. The statistical
conclusions changesignificantly when non-gravitational effects are included in the analysis. 相似文献
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