A B S T R A C TWe introduce a new approach to meteoroid stream identi®cation, based on a distance function involving four geocentric quantities that are directly linked to observations; the new distance function is thus de®ned in a space that has as many dimensions as the number of independently measured physical quantities, at variance from the conventional orbital similarity criterion of Southworth & Hawkins. Two of the new variables turn out to be near-invariant with respect to the principal secular perturbation affecting meteoroid orbits, the one associated with the cycle of q.
NEOs come close to the Earth's orbit so that any dust ejected from them, might be seen as a meteor shower. Orbits evolve rapidly, so that a similarity of orbits at one given time is not sufficient to prove a relationship, orbital evolution over a long time interval also has to be similar. Sporadic meteoroids can not be associated with a single parent body, they can only be classified as cometary or asteroidal. However, by considering one parameter criteria, many sporadics are not classified properly therefore two parameter approach was proposed.
Abstract. The complete characterisation of the Tunguska event of 30th June 1908 is still a challenge for astrophysicists. We studied the huge amount of scientific literature to select data directly available from measurements and we introduced parameters calculated by the application of models, and evaluated other possibilities. We then selected a range of meaningful atmospheric trajectories, from which we extracted a set of possible orbits. We obtained 886 orbits, which were used to estimate the probabilities of the possible origin of the Tunguska Cosmic Body (TCB). We found that the probability that the TCB moved on an asteroidal path is higher than it moved on a cometary one, 83% to 17%, respectively.
A B S T R A C TThe new criterion D N for meteoroid stream identi®cation, based on variables directly linked to observations, is applied to a set of 865 photographic meteor orbits and the results are compared with those obtained using the well-known and widely used D SH criterion of Southworth & Hawkins, using thresholds for meteor association computed according to Jopek & Froeschle Â. For 15 streams, including the Lyrids, the a Capricornids, the Perseids, the Taurids, the Quadrantids, the Geminids, the Leonids, the Orionids and the southern d Aquarids, the two searches are in very good agreement, with D N often adding a few more members to some streams, at the same level of statistical signi®cance as used for D SH . The Andromedids and the j Leonids, identi®ed as populous streams using D SH , are not recognized using D N ; on the other hand, using D N ®ve additional streams are identi®ed, namely the « Geminids, the Monocerotids, the northern d Aquarids and the rather populous a Virginids and « Piscids. In general, D N gives results essentially equivalent to those obtained with D SH in many circumstances, the most notable exception being for near-ecliptical streams, where the results differ markedly. We show also that the reduced distance function D R can be successfully applied to search for meteor showers resulting from the same meteoroid stream; in our study the Quadrantids and the southern and northern d Aquarid showers have been identi®ed as possibly being originated by a single meteoroid stream.
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