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The remaining critics of the small comet theory
eagerly awaited the results of the survey of the seasonal variations of
the frequency of small comet impacts into our atmosphere with the Polar
spacecraft. Years before, the atmospheric hole rates as determined by the
The question arises as to where is the location of the source of this
small comet population which is seen in the vicinity of Earth. We know
from the orbits of the small comets as determined from the speeds of the
atmospheric holes and from ground-based telescope observations that these
objects are moving more or less in the ecliptic plane. That is, their
motions are in the same general planes as those of the planets. Their
speeds at Earth are such that their orbits will carry them to Jupiter's
The large numbers of the small comets in the vicinity of Earth provide stimulation of numerous questions on the horizon. Among these are:
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camera on board Dynamics Explorer 1 had been shown to be correlated with
radar meteor rates observed with a ground-based station in Canada. The
relevant Dynamics Explorer-1 observations were taken during November 1981
through January 1982 and those with the radar during November 1955
through January 1956, some 26 years earlier. The remarkable correlation
of the seasonal variations as observed with these entirely different
instruments was dismissed as happenstance by the critics. Their
responses to these measurements are characterized by the donated
photograph in Figure 23 [left]. When the Polar seasonal results were
reported, and they most certainly were expected to disagree with the
previous findings, then we would have shot ourselves in the foot and the
small comets would be past history.
The Polar results were recently reported. Much to the dismay of the
critics the seasonal variations agreed with the previous measurements
with Dynamics Explorer 1 and the Canadian ground-based radar station. The
observations from all three of these instruments are shown in Figure 24
[right]. The agreement is truly remarkable and there is no chance it is
due to any error. From top to bottom are shown the rates for Polar,
Dynamics Explorer, and the Canadian radar. The features of these rates
are a maximum intensity during early November, a brief plateau during
mid-November, more or less constant rates during late November through
mid-December, another plateau of lesser intensities during mid-December
through early January, and a well-defined minimum in mid-January with
subsequent recovery. There is a further important feature of the radar
observations to be seen in Figure 24. That is the large increases of
rates associated with the atmospheric impacts of stony and iron meteors
during such well-known showers as the Leonids and the Geminids. As
expected because these are very small objects relative to the dimensions
of a cometary water cloud there is no sign of these meteor showers in the
Polar or Dynamics Explorer-1 records. The Canadian radar records both
the meteor showers due to stony objects and the background events which
are due to the infalling small comets.
orbit and beyond. Their origins most likely lie beyond the planets, in a
disk of comets which was formed during the birth of our solar system. A
diagram of this disk, sometimes called the Oort inner cloud after the
famous astronomer Jan Oort, is depicted in Figure 25 [left]. This sketch
is not to scale for, if it were, the planets would be drawn so close to
the Sun as to be not discernible. This disk extends for tens of thousands
of Astronomical Units (AU), with 1 AU being the distance of our planet
from the Sun. The gravity of passing stars or a, as yet undetected, dark
planet can disturb comets in the disk and scatter them into the inner
solar system of planets. Evidence of such a disk of comets, presumably
both large and small, comes from the existence of a large spherical cloud
of comets, the Oort cloud, which is also indicated in Figure 25. Their
original location is thought to be in the inner cometary disk until their
orbits were changed by passing large bodies such as stars.