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MIACMeteorite Observation and |
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MIACMeteorite Observation and |
Twelve meteor tracking
stations were established across the Prairie provinces
in 1969, in a network stretching from Alonsa, Manitoba in the East to
Lousana,
Alberta in the West. They were situated sufficiently close together for
a meteor to be recorded at two or more sites. The recorded tracks would
then permit calculation of both the orbit in space and also the likely
area of fall. The situation in the central and southern parts of the
Prairies
where farmland is dominant, maximised the chances of recovering samples
of any meteorites believed to have fallen. (Camera Stations had
previously
been established in Czechoslovakia and the U.S.A.). (Courtesy National
Research Council of Canada; Ref. Halliday et al. (1978): J. Royal
Astronom.
Soc. Canada, v. 72 p. 15-39)
This
is one of 12 identical observation stations which stretched across
the Prairie Provinces. In the roof area 5 cameras were mounted to
record
the night sky and any meteor tracks that happened to fall within the
view
of the cameras. A sector rotating in each camera at a known and precise
rate allowed a determination of the duration of the event and hence the
speed (see slide 12). The MORP network was dismantled in 1985.
(Courtesy
of the National Research Council of Canada)
A
rare photograph of a daytime fireball. What is seen here is actually
not the luminous fireball itself but rather the fine debris from its
ablation
and final detonation. This is clearly apparent from the somewhat
irregular
line of dust which has already been affected by upper level winds. The
trail of a fragment from the detonation can be seen plunging earthward
near the centre of the picture.
The
slide shows the path of a meteorite as recorded by one of the MORP
stations. The trail is segmented because a filter wheel rotated in
front
of the camera lens to produce four segments/second. Thus the duration
of
the passage through the atmosphere seen here took some 10 seconds. The
early part of the track, that above an altitude of 55°, was
lost in
the Station's blind spot. The slide is reproduced courtesy of the
National
Research Council of Canada.
INNISFREE is
one of only the few meteorites that have been recovered after the
passage
through the atmosphere has been accurately recorded photographically by
cameras at more than one place. Others include PRIBRAM, Czechoslovakia
and LOST CITY, U.S.A. Photographic data recorded at two or more
localities
permit the orbits of meteorites to be calculated as well as allowing
the
likely area of fall to be predicted. Note that the aphelia (farthest
points
from the sun) of INNISFREE, LOST CITY and PRIBRAM all lie in the
Asteroid
belt between Mars and Jupiter. INNISFREE belongs to the LL group, LOST
CITY and PRIBRAM to the H group of ordinary chondrites.
This
slide shows the first fragment of INNISFREE as it was found. It proved
to be the largest mass, weighing about 2 kg. Note how it sits on the
snow
with hardly any suggestion of a crater. During winter when the soil is
frozen, a meteorite that simply falls under its own weight may
penetrate
a layer of snow and then bounce back to the surface off the frozen soil
beneath. Thus, while snow is on the ground the possibilities for
recovery
are often best. The thin black fusion crust which covers most such
meteorites
if they have not disintegrated on impact, provides a strong contrast
with
the pure white of the snow. (Courtesy National Research Council of
Canada;
Ref.: Halliday et al.,1978, J. Roy. Astronom. Soc. Canada, v. 72 p.
15-39)
The
INNISFREE (Alberta) meteorite fell 13 km north of the town of this
name at 7.17 pm on February 5th, 1977. An immediate search of the area
by light plane and on foot, turned up nothing, but photographic records
from two stations in the MORP network allowed a computer prediction of
the most likely fall area. Dr. Ian Halliday of the Herzberg Institute
of
Astrophysics led an N.R.C. sponsored party to search the area some
eleven
days later. Within a few hours the first and largest piece (2.07 kg)
had
been found only a few hundred yards from the point predicted by the
computer
program. Subsequently 5 other fragments were found, bringing the total
mass recovered to 3.79 kg. The meteorite turned out to be an LL5
hypersthene,
olivine chondrite breccia and thus a member of a relatively rare group.
It is a particularly important meteorite because its orbit in space has
been calculated from the photographic data (see above; Ref.: Halliday
et
al., 1978: J. Roy Astronom., Soc. Canada, v.72 p. 15-39; D.G.W.
Smith,1980,
Can. Min. v. p. 433-442).
MIAC Slide Group and Michael Higgins