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Harvard Astronomer Is Second Man To Calculate Course of Meteorite

By Mark W. Oberle

For the second time in the history of astronomy, the orbit of a meteorite has been calculated to extend out to the asteroid belt between Mars and Jupiter.

Richard E. McCrosky, lecturer in astronomy, used a series of photographs taken near Lost City, Oklahoma, on Jan. 3 to track the fiery descent of a meteorite and calculate its elliptical orbit.

A five-man search party headed by McCrosky has recovered two of the metcorite's fragments, and the shortlived isotopes in these samples are being measured at the Smithsonian Astrophysical Observatory here, and at other installations.

At first glance, McCrosky's orbital calculations would seem to support the theory that many meteors originated in the asteroid belt, a jumble of orbiting planetary material just this side of Jupiter.

But McCrosky has his doubts.

"The average age of this type of meteorite is about 60 million years," he said yesterday, 60 million years is a very short time on an astronomical scale.

A Mighty Powerful Mechanism

"No one has yet found a mechanism that can move an asteroid from the asteroid belt into an earth-crossing orbit in such a short time. The only way would be a truly catastrophic event, and we would see shock effects in the meteorite if such an event occurred," McCrosky added.

Edward L. Fireman, lecturer on astronomy, has started analyzing a 54-gram sample from the Lost City meteorite.By measuring two isotopes of the element Argon in this sample, he will determine how long the meteorite has been exposed to the sun's radiation. Exposure ages for this type of meteorite commonly range from 25,000 to 400 million years.

The meteorite's isotopes composition may also give some idea of how the sun's activity has changed in the past.

Fireman used a similar isotope technique to calculate the age of lunar samples from Apollo 11.

Farmer Finds A Piece

The original Lost City meteorite probably weighed several hundred pounds, and it created a bright "fireball" trail that was seen by thousands of prairie dwellers before it exploded. A farmer named Phillip Halpain discovered a 9-ounce fragment of the meteor while he was searching for a lost calf. Earlier, a member of the Smithsonian's search party discovered a 21 pound chunk lying on a dirt road.

The recovery caps five years of observations by the Smithsonian's Prairie Network, a system of 16 automatic camera sites that continously photographs the night sky in seven Midwestern states.

Hundreds of meteors' orbits have been calculated from these photographs, and search parties have looked for meteorite fragments twice before. But this is the first time the Network's scientists have been able to recover a fragment and also calculate its orbit.

The only other record of this kind occurred in Czechoslovakia in 1959.

Bronzite Chondrites

Some 35 per cent of meteorites, including the Lost City specimen, are classified as bronzite chondrites-an iron-rich type that contains glassy beads. "This is a very common, garden variety of meteorite," a Smithsonian spokesman said last week.

"But that is better for the scientists. It provides a good calibration for all the thousands of other meteors that have been photographed but never recovered," he concluded.

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