Allende meteorite

The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and over 2 tonnes (tons) of meteorite were recovered. The availability of large quantities of samples of the scientifically-important chondrite class has enabled numerous investigations by a large number of scientists; it is often described as 'the best-studied meteorite in history.' The Allende meteorite has abundant, large calcium-aluminium-rich inclusions, which are among the oldest objects formed in the Solar System.a. ^ The number of specimens and total weight can never be known with certainty. Clarke et al. (1971) reported that 'At least two tons of meteoritic stones have been recovered.' Hundreds more have been found since it was published. The Allende meteorite is the largest carbonaceous chondrite ever found on Earth. The fireball was witnessed at 01:05 on February 8, 1969, falling over the Mexican state of Chihuahua. After breaking up in the atmosphere, an extensive search for pieces was conducted and over 2 tonnes (tons) of meteorite were recovered. The availability of large quantities of samples of the scientifically-important chondrite class has enabled numerous investigations by a large number of scientists; it is often described as 'the best-studied meteorite in history.' The Allende meteorite has abundant, large calcium-aluminium-rich inclusions, which are among the oldest objects formed in the Solar System. Carbonaceous chondrites comprise about 4 percent of all meteorites observed to fall from space. Prior to 1969, the carbonaceous chondrite class was known from a small number of uncommon meteorites such as Orgueil, which fell in France in 1864. Meteorites similar to Allende were known, but many were small and poorly studied. The original stone is believed to have been approximately the size of an automobile traveling towards the Earth at more than 10 miles per second. The fall occurred in the early morning hours of February 8, 1969. At 01:05 a huge, brilliant fireball approached from the southwest and lit the sky and ground for hundreds of miles. It exploded and broke up to produce thousands of fusion crusted pieces. This is typical of falls of large stones through the atmosphere and is due to the sudden braking effect of air resistance. The fall took place in northern Mexico, near the village of Pueblito de Allende in the state of Chihuahua. Allende stones became one of the most widely distributed meteorites and provided a large amount of material to study, far more than all of the previously known carbonaceous chondrite falls combined. Stones were scattered over a huge area – one of the largest meteorite strewnfields known. This strewnfield measures approximately 8 by 50 kilometers. The region is desert, mostly flat, with sparse to moderate low vegetation. Hundreds of meteorite fragments were collected shortly after the fall. Approximately 2 or 3 tonnes of specimens were collected over a period of more than 25 years. Some sources guess that an even larger amount was recovered (estimates as high as 5 tonnes can be found), but there is no way to make an accurate estimate. Even today, over 40 years later, specimens are still occasionally found. Fusion crusted individual Allende specimens ranged from 1 gram (0.035 oz) to 110 kilograms (240 lb). Allende is often called 'the best-studied meteorite in history.' There are several reasons for this: Allende fell in early 1969, just months before the Apollo program was to return the first moon rocks. This was a time of great excitement and energy among planetary scientists. The field was attracting many new workers and laboratories were being improved. As a result, the scientific community was immediately ready to study the new meteorite. A number of museums launched expeditions to Mexico to collect samples, including the Smithsonian Institution and together they collected hundreds of kilograms of material with CAIs. The CAIs are billions of years old, and help to determine the age of the Solar System. The CAIs had very unusual isotopic compositions, with many being distinct from the Earth, Moon and other meteorites for a wide variety of isotopes. These 'isotope anomalies' contain evidence for processes that occurred in other stars before the Solar System formed. Allende contains chondrules and CAIs that are estimated to be 4.567 billion years old, the oldest known matter (other carbonaceous chondrites also contain these). This material is 30 million years older than the Earth and 287 million years older than the oldest rock known on Earth, Thus, the Allende meteorite has revealed information about conditions prevailing during the early formation of the Solar System. Carbonaceous chondrites, including Allende, are the most primitive meteorites, and contain the most primitive known matter. They have undergone the least mixing and remelting since the early stages of Solar System formation. Because of this, their age is frequently taken as the 'age of the Solar System.'