Peter Brown (1), Alan R. Hildebrand(2), Daniel W. E. Green(3), Denis Page(4),
Cliff Jacobs(5), Doug Revelle(6), Edward Tagliaferri(7), John Wacker(8)
and Bob Wetmiller(9)
1. Department of Physics, University of Western Ontario, London,
Ontario, N6A 3K7, Canada.
2. Geological Survey of Canada, Natural Resources Canada, Continental
Geosciences Division, 1 Observatory Crescent, Ottawa, Ontario, K1A 0Y3,
Canada.
3. Smithsonian Astrophysical Observatory, 60 Garden Street, Cambridge, MA
02138, USA.
4. Federation des astronomes amateurs du Quebec, 7642 Boul.\
Shaughnessy, Montreal, Quebec, H2A 1K4, Canada.
5. Sandia National Laboratories, Org. 5909, MS 0978, P. O. Box
5800, Albuquerque, NM, 87185, USA.
6. Los Alamos National Laboratories, P. O. Box 1663, Los Alamos, NM, 87545,
USA.
7. ET Space Systems, 5990 Worth Way, Camarillo, CA, 93012, USA.
8. Battelle, Pacific NW Laboratories, Richland, WA, 99352, USA.
9. Geological Survey of Canada, Natural Resources Canada, Pacific
Division, 1 Observatory Crescent, Ottawa, Ontario, K1A 0Y3, Canada.
The St. Robert (Quebec, Canada) meteorite shower (H5 chondrite) occurred on 1994 June 15 at 0h02m UT. The fireball was recorded by visual observers in the US and Canada as well as by optical and infrared sensors onboard satellites operated by the US Department of Defence. The fireball endpoint occurred at an altitude of 36 km northeast of Montreal, at which time the object underwent several episodes of fragmentation. In all, some 20 fragments totalling 25.4 kg were recovered in an ellipse measuring 8 by 3.5 km. Interpretation of all available data indicate that the fireball traveled from south-southwest to north-northeast, with a slope from the horizontal of 55-61 degrees. The most likely heliocentric orbit for the body prior to collision with the Earth suggests an entry velocity near 13 km/s with the meteoroid moving in a low-inclination orbit and having orbital perihelion located extremely close to the Earth's orbit. From satellite optical data the photometric mass consumed during the largest detonation is found to be approximately 1200 kg. Estimation of the source energy from acoustic considerations yields 0.5 kilotons TNT equivalent energy, corresponding to a mass of order 10 metric tons. This measure is uncertain to approximately one order of magnitude. Modelling of the entry of the object suggests a mass near 1600 kg, in good agreement with the satellite optical data. Cosmogenic radionuclide activities constrain the lower initial mass to be 700 kg while the upper limit from these same data is approximately 4000 kg. Seismic data possibly associated with the fireball suggest extremely poor coupling between the airwave and the ground. The St. Robert meteorite demonstrates that satellite observations offer the potential to derive masses and orbits of Earth-crossing meteoroids which are beyond the detection limits of current telescopic search programs. Having ground truth from the St-Robert meteoroid also allows calibration of satellite observations both phenomenologically and on a theoretical level.