Figure 18. Photomicrograph showing a glass rind around a stony spherule.
above the bottom and no trace of particle trans-
deposits on the ice surface, estimated the age of
port even with the collector nearby to act as a lo-
the ice melted to form the deposits using an ice
cal disturbance. Perhaps the compressed air en-
flow model, and assumed that all particles depos-
trapped in the ice releases bubbles into the water
ited had been collected. We have calculated a ter-
as the well melts downward, and this agitation
restrial flux rate for melted micrometeorites larger
than 250 m for the pocket (7 106 g m2 yr1)
helps to entrain the micrometeorites.
and the plateau (6 107 g m2 yr1) collections;
It is not clear whether or not the particles are
being removed from the plateau into the pockets;
the latter is the same value found by Maurette et
al. (1987) for their 250300-m size fraction. We
the micrometeorites in the pockets may come from
the well sides. If micrometeorites are not being
know the volume of firn and ice melted to 10%
moved from the plateau area, repeat collections
and the age of the ice to 50 years (the uncertainty
of the plateau could provide information on flux
is due to the topography at the bottom of the well),
rates and on any temporal changes in the type and
and the area cleaned was determined from the
number of micrometeorites. Detailed analysis of
video. Since we collected from 7% of the well bot-
the separate collections from the central plateau
tom, the accuracy of our flux measurement will
and the isolated pockets will reveal the degree of
depend on the movement of particles along the
micrometeorite concentration possible by the cir-
bottom.
culating flow.
From the video footage we estimate that we col-
lected from an area of 30 m2, or about 7% of the
well bottom. The pockets preferentially contain
iron-oxide grains derived from the water-supply
CONCLUSION
system; the circulating flow can easily concentrate
We have successfully recovered extraterrestrial
this injected material. The order-of-magnitude-
materials from a polar well. This is thought to be
larger flux estimate for the pocket as compared
one of the largest and best preserved collection of
with the plateau, however, suggests that the well
circulation is also concentrating micrometeorites
micrometeorites, and it is the best dated. This col-
into the pockets. This is despite the relatively small
lection will allow us to calculate flux measure-
ments of cosmic dust larger than 50 m and will
flow rate (about 1 L s1) discharged about 13 m
21
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