Sizes of Impacting Leonids

What is the nature of the impacting meteors? Several different 
models have been used, the most recent being by Artemieva, Shuvalov, 
and Trubetskaya presented in a poster at this conference on Tuesday.  
Using numerical simulations, they have determined that a magnitude 3 
flash could be produced by a particle 3 kg in mass, and that the 
smallest reported impact, at magnitude 7, could have been produced 
by a 25 g meteor. This seems to be in reasonable agreement with the 
expected largest particles in the Leonid meteor stream that hit the 
Moon.  Artemieva et al. derived a luminous efficiency of about 
1/1000 of the kinetic energy for the Leonids lunar impact velocity 
of 72 km/sec. In addition, Artemieva et al. found that the density 
of the impacting meteors must be at least 1 gram/cm3 in order for 
the flashes to have appeared on two half-frames of our videotapes.  
The results of these and other authors are given in the table below. 
Beech and Nikolova's estimates are much lower than the others. 
Apparently, they used an unrealistically large assumption for the 
luminous efficiency of the impacts. There is still considerable 
uncertainty in the actual luminous efficiency of these impacts that 
occurred at much higher velocities than any existing experimental 
data, and therefore in the sizes and masses of the impacting 
meteors. But the meteors are likely to range in size from that of 
lemons to watermelons.  In any case, the craters on the Moon 
produced by these meteors will be very hard to find since they are 
likely only a few to several meters in diameter, while the 
uncertainty in their locations is many kilometers. 

Prepared 2000 May 4; Corrected 2000 June 21

References:
Gehring, J.W.; Charters, A.C.; & Warnica, R.L. (1964).  "Meteoroid 
       Impact on the Lunar Surface."  In: Salisbury & Glaser (1964), 
       pp.215-263.
LaPaz, Lincoln (1938).  "The Atmoshpere of the Moon and Lunar 
       Meteorite Erosion."  Popular Astronomy, 46, No. 5, pp.277-282.  
Westfall, John E. (1998) "Worthy of Resurrection: Two Past ALPO 
       Lunar Projects." Proceedings of the 48th Convention of the Assoc. 
       of Lunar & Planetary Observers and ALPO Monogram No. 7. 
Artemieva, N.A., Shuvalov, V.V., and Trubetskaya, I.A., "Lunar 
       Leonid Meteors - Numerical Simulations", Lunar and 
       Planetary Science Conference, Paper 1402. (Texas, 2000 
       March).  This paper can be downloaded from the LPSC conference
       Web site.  The file is sess33.pdf, the file for the
       session called "Impact Theory and Experiment" under
       Tues. Evening, Poster Session I.