Optical Search for High Meteors in Hyperbolic Orbits

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Abstract
Dual-station image intensified television studies have indicated very few meteors at heights greater than 120 km, and few statistically significant hyperbolic orbits. However, the optimum intersection height for these studies was about 95 km, and the relatively small fields of view resulted in a bias against high (and therefore fast) meteors. We have developed height sensitivity correction factors, and found that short baseline television studies resulted in relatively little bias against high meteors, and the absence of meteors above 120 km appears to be real. We report preliminary results from a three-station, image-intensified video meteor detection system sensitive to apparent magnitude about +9.5 with optimum intersection heights 115-125 km. We have detected neither particularly high meteors nor meteors in clearly hyperbolic orbits. We conclude that the proportion of true hyperbolic meteors in the mass range 10-4 to 10-6 kg is less than a few percent, and that optical meteors corresponding to meteoroids in this mass range do not ablate at heights above approximately 120 km. We suggest several ways to reconcile these results with southern hemisphere radar studies.

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