The Prairie Meteorite Search

Meteorites have been accumulating on the Canadian land mass since the end of the last glaciation, approximately 10,000 years ago. The current rate of fall for meteorites >100 g mass (surviving to the ground) is ~27 per year per 106 km². With a 10,000 year integration time, and presuming that fragmentation by atmospheric breaking produces a five-fold increase in number, this rate implies that ~14 meteorites >100 g mass occur in each 10 km2 (~3.5 in each section). Meteorites are generally found by eye, so that any surface upon which rocks are distinct is favourable for recovery, such as sea (or lake) ice or barren desert. Any type of high standing vegetation substantially reduces recovery chances.

In Canada agricultural land has been the most prolific meteorite producing surface. In addition to being unvegetated for part of the year (and cut short after harvest), farmers have an “intimate” relationship with their fields and the rocks thereon. Rock picking is both a seasonal and perpetual activity, and simple curiosity has led to the known recovery of 26 meteorites by farmers on the Canadian prairies to date. The typical cues that lead farmers to suspect a rock as a meteorite are unusually high density and unusual, sometimes rusty, appearances. The Prairies are Canada’s outstanding recovery surface being the largest cultivated area; the farmed portion of southern Ontario has produced meteorites at a comparable rate.

The Prairie Meteorite Search uses the method pioneered by Harvey Nininger seventy years ago in the southern American states to recover meteorites. The method involves making it easy for farmers to have unusual rocks identified that they feel might be meteorites. Campaigns of local publicity, primarily through putting articles in local newspapers, alert residents of a rural area to an opportunity to have their suspected meteorites identified at a central place such as a museum, school, or library. Meteorite samples are also displayed so that anyone may see their characteristics. The rockier Canadian prairies have a lower “signal to noise” ratio than the unglaciated southern American states, but the Prairie Meteorite Search has recovered four meteorites in the summers of 2000 and 2001, bringing Canada’s recovered total to 61 meteorites to date. The average ratio of genuine meteorites to “meteor wrongs” for this search is approximately 1 in 400. Based on the area covered, and how and when meteorites have been found, one may estimate that farmers on the Prairies have recovered more than 100 meteorites, most of which remain unknown to the research community.

(Additional project information may be seen at http://www.ucalgary.ca/prairie_meteorite_search/)