What is the St- Robert meteorite?
On the evening of June 14,1994, around 8:00 p.m. EDT, thousands of people in Ontario, Québec and the northern United States witnessed a spectacular fireball accompanied by a very loud sonic boom. Some 10 to 20 kilometres above the Earth's surface, the meteor exploded, showering fragments over southern Québec. Minutes later, one of these was recovered by Stephane Forcier on his family's farm in St-Robert de Sorel, east of Montréal. The following day, this piece was confirmed by the Geological Survey of Canada (GSC) to be a meteorite. Because numerous pieces of the same composition have been found, the event is called the St- Robert meteorite shower. Hundreds of fragments of the St-Robert meteorite are believed to have fallen, but only about 20 have so far been recovered.
Why are meteorites important?
Meteorites are rocks from outer space that have fallen to earth. Although meteorite falls occur every day around the world, the recovery of fragments is rare, since the falls are usually unwitnessed and/or the fragments land in remote, uninhabited areas or in bodies of water.
Meteorites are an invaluable source of information about outer space, and they have been used by scientists to learn about the universe since long before space travel was possible. Because most meteorites date from the origin of the Earth, 4.6 billion years ago, they provide clues about the nature and origin of our solar system and the interior of planets. Some are believed to be samples of the Moon and Mars or pieces of comets, but most are probably fragments of asteroids.
Why is the St-Robert meteorite unique?
The St-Robert event is rare for several reasons. Most important, the fall yielded a number of scientifically valuable fragments that were recovered within hours or days of landing. It is also probably known about by more people than any other meteorite fall, thanks to modem communications and the fact that the meteorite landed near a heavily populated area.
The recovery and analyses of the Forcier fragment may be the quickest ever recorded. Stephane Forcier and his brother Serge located it in a pasture shortly after hearing something tumbling in the air and falling near the family farmhouse. With the help of curious cows, the brothers found a 15 cm hole from which they dug up a grapefruit - sized, cold, blackened stone weighing 23 kg. Stephane informed the police of the find, and St-Robert immediately became a centre of media attention. On June 15, the GSC identified the fragment and borrowed it from the Forcier family. Within 68 hours of recovery it was taken to the Battelle laboratory in Richland, Washington to measure short-lived cosmically induced changes in the chemistry of the meteorite. The results of these analyses will allow scientists to estimate the length of time in orbit, as well as the age, size, and origin of the parent body.
The St-Robert meteorite is also the first stony meteorite (composed primarily of silicate minerals) to be found in Québec. It is only the 12th recorded fall in Canada since 1887, and the first meteorite shower in eastern Canada.
What do fragments from the St-Robert meteorite look like?
Fragments from the St-Robert meteorite have a thin, black crust on the surface, and this may flake off to reveal a grey/white interior with bits of white and bronze metal. When meteorites are exposed to air and water, the crust turns brown and rust stains form around the metal in the exposed interior. The fragments may be quite rounded, angular, or have a combination of smooth and sharp surfaces. Anyone finding a meteorite should record precisely where and when they found it and keep it dry.
What has happened to the Forcier fragment?
The GSC purchased the first fragment recovered by the Forcier family for $10,000. It is now part of the National Meteorite Collection of Canada, held by the GSC since 1855. This collection contains 700 specimens from some 400 sites worldwide. The fragment will be preserved for further scientific research and used for public display, including a special exhibit on the St- Robert fall at the Montréal Planetarium
Who owns meteorites, and what monetary value do they have?
Meteorite fragments that fall on private property belong to the property owner and may be held or sold by the owner.
The normal market value for stony meteorites is $3.00 to $150 per gram. The GSC paid slightly more for the Forcier fragment because of its scientific, cultural and historical importance.
When a meteorite is donated to a cultural institution, the donor may be entitled to a tax credit or exemption. However, profits from the sale of a meteorite to a non-cultural institution or a private collector are taxable. Information on the tax implications of selling or donating a meteorite is available from Revenue Canada.
A special permit is required to export meteorite fragments, which are considered to be cultural property. Exporting without such a permit is a criminal offence. Information on how to obtain a permit is available from Canada Customs.
For further information on the St-Robert meteorite or meteorites in general contact:
Richard
Herd,
National
Meteorite
Collection,
Geological
Survey
of
Canada,
601
Booth
Street,
OTTAWA
K1A
0E8
(613) 998-0381
Preliminary technical data on the St-Robert meteorite:
Type of meteorite: H5 chondrite comprising about 30% chondrules of olivine and orthopyroxene (bronzite), 10% iron (kamacite with minor taenite), and 5% troilite, in a groundmass of finer- grained orthopyroxene and olivine with small amounts of accessory plagioclase and chromite
Presumed source: Asteroid belt
Mass on entering atmosphere: Estimated 10 to 100 tonnes
Mass at explosion: Estimated 100 to 150 kilograms
First visible at: 100 kilometres above surface
Ellipse of fall: Approximately 4 km by 7 km
Largest fragment recovered: 6.5 kg
Smallest fragment recovered: 55 g
Gamma ray spectroscopy: Revealed a greater range of short-lived isotopes (including Be-7 and Na-24) than normally seen in meteorites.
Richard
Herd