Stream and sporadic meteoroids associated with near-Earth objects

Abstract

Near-Earth objects (NEO) are objects that come close to the Earth's orbit. If dust is ejected from them through any process, a meteoroid stream will form which may be seen on the Earth as a meteor shower. As orbits evolve rapidly in this region of the Solar system, a similarity of orbits at the present time is not sufficient to prove a relationship; integrations are needed to show that the evolution over a substantial period of time is similar. Characteristics of streams where the parent is a comet and dust is ejected over a range of values of true anomaly and over several orbits will be very different from a stream formed through the ejection from an asteroid which is likely to occur at a single point in time. Hence a study of meteoroid streams related to NEO may tell us whether the NEO is a comet or an asteroid. In particular, several showers can be associated with the same stream if it is from a cometary origin. Sporadic meteoroids cannot be associated with a single parent body. We can classify them only as of cometary or asteroid origin. In the past, for this purpose several dynamical criteria have been proposed. e.g. K-, Q-criterion, and they were applied to the present-day orbits. We have shown that such an approach may introduce a serious bias into the results – the fraction of cometary orbits can be understated by up to 29 per cent. To remove such a bias, we propose that a two-parameter criterion is used. Assuming that comet and near-Earth asteroids (NEA) populations are disjoint, the Q-i and E-i criteria proved to be the most reliable tool for dynamical discrimination of the NEO population. Using these criteria we have found that in our sample of sporadic meteors cometary type orbits predominate, in a set of ∼78 000 sporadic meteoroids 66–67 per cent have cometary type orbits. This fraction can differ for meteors observed by different technique; in general, it decreases with decreasing brightness of the observed meteors.