Geophysical Aspects of Meteors

Abstract

Although few meteors are visible to the unaided eye under normal clear sky conditions the total number entering the earth’s atmosphere every day is very great. The majority of these meteors are minute pieces of stone or iron moving in closed orbits in the solar system. Occasionally the earth encounters concentrated groups of meteors known as showers, and these provide the most spectacular part of meteoric phenomena in which the visible hourly rate may rise to a hundred for a few nights. Even so these shower meteors contribute not more than 10 to 20% of the total meteoric influx; the remainder move in ungrouped orbits and are classed as sporadic meteors. There has, in the past, been a cleavage of opinion about the origin of the sporadic meteors. Some workers believed that they have an origin in interstellar space and move in hyperbolic orbits around the sun. However, the radio echo measurements during the past few years have not supported this belief and it is now generally agreed that these sporadic meteors move in short period orbits around the sun and essentially belong to the solar system. With regard to the shower meteors, many of these move in cometary orbits, although the relationship with particular comets is not clear in many cases.