Location
Where are meteorites found?
​ Where are the craters, witnesses of past impacts on Earth?
(c) Meteorite Recon
Although meteorites can be observed falling to Earth, most are found in hot or cold deserts, which preserve them and allow to identify them more easily. Moreover, the annual expeditions in the various deserts carried out by teams of meteorists, as well as the observation of the sky thanks to the large deployed camera networks make it possible on one hand to find numerous meteorites and, on the other hand, to observe falls and determine possible fall points of the samples.
Hoba meteorite
Crédit: Sergio Conti- CC 2.0
98% of meteorites recovered on Earth are finds, which may have had a residence time on Earth sometimes of several hundred thousand years.
Hoba is the largest meteorite ever found in 1920 in Namibia. It is a 60 tons iron meteorite, 2.7 meters long and 0.9 meters wide. It has been estimated that Hoba fell to Earth 80,000 years ago.
Many missions are launched to recover the finds, especially in hot and cold deserts which allow preservation for very long periods of time. Cold deserts, such as Antarctica, represent 70% of the finds while hot deserts, such as the Atacama Desert represent 25% (Gattacceca et al., 2011). The hyper-aridity of hot deserts and the ice of Antarctica contribute to the preservation of these objects for thousands of years, without forgetting that they are more remarkable in a desert environment.
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In the USA, the ANSMET project (Antarctic Search for Meteorites program) organizes annual expeditions to recover meteorites, and has enabled the collection of more than 22,000 samples to date.
NASA/Cindy Evans
It has been observed that more than half of the meteorites falling on Earth fragment upon entering the atmosphere. The different fragments are therefore paired as they come from the same meteorite initially. Depending on the speed, inclination and composition of a meteoroid, it is possible to find fragments over several kilometers.
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On the left, several fragments from Allende carbonaceous chondrite, felt in Mexico in 1969.
Allende fragments - Crédit: Gaeton Faraone/ NASA/Science Photo Library
Some 190 craters have been identified on the Earth's surface. One of the most famous, Meteor Crater in Arizona, is a crater of 1.2 km in diameter, formed during the fall of an iron meteorite Canyon Diablo 50,000 years ago, of which 30 tons were recovered. Another well-known crater is that of Chicxulub in Mexico, reputed to have formed 65 million years ago and to have participated in the extinction of the dinosaurs.
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On Earth, craters fade over time, due to erosion phenomena that constantly redraw the Earth's surface. On the Moon, on the other hand, no phenomena can erase an impact crater, except for another crater, leaving the surface of the Moon totally impacted.
Meteor Crater
The sky observation, thanks to the installation of large camera networks, makes it possible to observe very frequently the falls of meteorites. By studying the trajectories of the falls, the researchers determine the potential areas where meteorite fragment or fragments have fallen and go in search of them - a search that can be fruitful. As such, many meteorites have been recovered, extraterrestrial samples which have been little or not altered by a long period of residence on Earth. The French Vigie-Ciel/FRIPON network and the Italian PRISMA network are part of the international networks that carry out these observations.
Figures
How many are there in the world today? To what frequency fall on Earth?
Identification
What are the characteristics that allow them to be recognized?
Origin
Where do they come from? How long do they wander around in interplanetary space?
