Orbital intersection External links: Structure of Taurid stream Encke trail Meteoroid swarm and Taurid fireballs Taurids (Gary W. Kronk)
Streams and showers
The Taurid Complex, related to Comet 2P/Encke, is a massive stream of material in the inner solar system. The following four diagrams schematically show four different Taurid orbits and the orbits of Earth and Jupiter.
The parts of the Taurid orbits above the ecliptic are shown as brighter and thicker lines than the parts of the orbits below the ecliptic. Comparison of the four diagrams shows that if an orbit is twisted around in 3-dimensional space, it can be brought to Earth intersection in different ways (the orbit intersecting the Earth's orbit before or after perihelion, and coming from above or below the ecliptic). Under the gravitational influence of Jupiter and the other planets, a Taurid orbit can reach each of those configurations in turn, over a period of some millennia. Solar system dynamics in a large part consists of studying such orbital evolution, or orbital precession, whether of meteor streams (such as the Taurids), comets, asteroids, satellite systems around planets, or the planets themselves.
The four diagrams show how different meteor showers can result from the same physical meteor stream. The Taurid stream contains particles (small, solid grains) at different stages of their precession cycles. The four meteor showers represented in the diagrams correspond to four cross sections through the stream, or equivalently four specific points in the precession cycle. Thus although the name "Taurids" refers to a nighttime meteor shower seen in the northern autumn, the shower in fact has two separate branches, Northern and Southern Taurids, radiating from north and south of the ecliptic. Particles are at different points in their precession cycles, i.e., the orbits have been twisted around (by the gravitational perturbations of the planets) to have different orientations in 3-dimensional space, so that they approach the Earth from north or south of the ecliptic. Similarly, particles from the same stream can hit the Earth after they pass perihelion, approaching the Earth from its daytime side. The northern and southern branches are respectively the zeta Perseids and the beta Taurids, these meteors being detectable by radio meteor methods during daytime in the northern summer.
The study of when a meteor stream can produce a meteor shower is the study of when precession brings orbits to intersection with Earth, or e.g. with Mars. The orbits of asteroids and comets can also be brought to Earth intersection by planetary precession; this relates to the Earth impact hazard.
Structure of Taurid stream
Armagh astronomers have from some time been interested in the Taurid stream, in building dynamical models of its structure, and of how it was formed. The stream is the debris of a large comet that was captured into the inner solar system twenty thousand or so years ago. This is long enough for the orbits of particles to have dispersed, so that all four shower branches are formed, and for particles to have also dispersed in longitude (so that meteors from the Taurids and related meteor showers can be observed over some months).
On the other hand, while the orbits of some particles are quite dispersed, it is still likely that the Taurid stream has a narrow and dense core consisting of particles concentrated near the orbit of the stream's parent object, which is presumably related to Comet 2P/Encke. As the orbits of the material constituting this narrow, dense core have been subject to perturbations over thousands of years, it may be inferred that intense bombardment episodes have resulted at epochs when the material reaches Earth intersection. Dynamical calculations show that, as a Taurid-like orbit precesses, the northern daytime intersection occurs just a little (a few centuries) before the southern nighttime one, and the southern daytime one just before the northern nighttime one. That is, the four intersections occur in two pairs, and the influx of material to Earth is enhanced during epochs lasting a few centuries and spaced by a few millennia. The term "coherent catastrophism" has been used by astronomers at Armagh and elsewhere to describe the idea that there are strong patterns in the influx of extraterrestrial material to Earth.
Meteoroid swarm and Taurid fireballs
Much wider than thE dense core, but less broad than the whole stream, is a meteoroid swarm that causes rather more Taurid fireballs to be seen in some years, compared to usual years.
Last Revised: 2005 November 4th
Go to HOME Page