Allende isn’t shrouded in mystery like the Orgueil meteorite fragments or the Tunguska Event. Scientists have a decent estimate of Allende’s age, and there were no shortage of Allende fragments for sampling. Because Allende has been studied so well, it’s possible that scientists and space enthusiasts alike have learned more about meteorites from studying Allende than they have from almost any other meteorite.
The Allende Meteorite fell on February 8, 1969, over the Mexican region of Chihuahua. The Allende Meteorite had a considerably large strewn field of 8×50km, over a flat stretch of mostly desert land, which made it ideal for collecting pieces. Since that time, there’s been 25-30 tons worth of Allende fragments collected, with some still being found as of 2009 and remaining a favorite among meteorite fragment collectors. Today, Allende fragments can be found where many other meteorites share a home with it within the Museum of Natural History.
For many scientists, Allende’s arrival was serendipitous. Allende fell in 1969, when the “Space Race” was reaching its peak. Agencies such as NASA, who were running the Apollo program, leapt at the opportunity to analyze and research the Allende meteorite. In the years of research since, they’ve been able to determine that Allende was formed by dust and gas conglomerating into a single mass over billions of years.
Non-scientific individuals who’ve found Allende fragments have noticed that an Allende fragment doesn’t look terribly different from any other Earth-based rock upon first glance, but the trained scientific eye would notice several special things about an Allende fragment.
Allende is classified as a CV3 carbonaceous chondrite, but unlike others of its type, it’s rich of an isotope known as O-16. Allende has a very diverse composition, with iron making up most of it while dozens of mineral and elements such as carbon helped form it. A trained scientific eye would definitely pick up on the many calcium and aluminum inclusions (CAI’s) within an Allende fragment; which is Allende’s most noticeable characteristic. If an individual were to crack open an Allende fragment and notice a very thin, white, and grainy substance fall from the fragment, this is a very distinctive ground known as “presolar grain”. From the presence of pre-solar grain alone, an individual can determine that a meteorite is at least 500 million years old, but the CAI’s within Allende have been estimated to be at least 4.5 billion years old. This gives Allende the distinction of containing the oldest matter currently on Earth in addition to the prime distinction of being the largest carbonaceous chondrite meteorite on Earth.
There are far too many facts known about Allende to speculate upon it like its mysterious “cousin” Orgueil, but Allende that is where Allende is most attractive: we can reliably learn from it.
Christopher L. Shelby, M.D.