General
Meteorites are privileged witnesses to the entire history of our solar system. How many are they? How often do they fall to Earth? How to identify them and where are they found? So many questions we answer here.
Denomination
Above all, it is important to know the name of the different objects and phenomena related to meteorites
Rocky debris from the solar system, of various sizes ranging from micrometers to meters, constantly enters the Earth's atmosphere. They are meteoroids .
The friction induced by the atmosphere on the rocky body, which arrives on average at a speed of around 20 km/s, i.e. approximately 1200 km/min and even 72,000 km/h, causes a luminous phenomenon, a trickle of light in the sky, which is called a meteor. As such, shooting stars themselves are in fact meteors, formed by the entry into the Earth's atmosphere of particles of the sand grain size. They heat up on contact with the atmosphere and disintegrate very quickly, which explains why the luminous phenomenon seen in the sky is very short. In larger rocky debris, the light trail is noticeable for longer seconds. Meteors whose luminous intensity is greater than that of Jupiter are called fireballs .
Depending on the size of the meteoroid, its speed, and its angle of inclination, it can come all the way to the Earth's surface (but also other planetary bodies). It is that piece of leftover rock that fell on Earth, having a minimum diameter of 10 microns, which is called a meteorite. On average, a meteorite represents only 10% of the initial mass of the meteoroid. Thus meteorites are the remains of rocky debris from different areas of the Solar System, which have made their way to us and which we can collect and study.
Read more: Rubin and Grossman, Meteorite and meteoroid: New comprehensive definitions, Meteoritics & Planetary Science 45, Nr 1, 114–122 (2010)
We distinguish falls from finds. Falls are meteorites that have been observed in the sky. They offer an inestimable quality because they have only undergone very limited terrestrial alteration. Meteorite falls are rather rare, although establishment of various sky observation networks has recently allowed more observations of meteorite falls. Finds, which represent 98% of meteorites, can be found up to several tens of thousands of years after the fall. These finds are mainly found in deserts. 95% of meteorites are indeed found in Antarctica or in the hot deserts of Sahara and Atacama.
Name
Meteorites are named after the place or city where they fell or were found . Thus, meteorites have town name such as Paris or are called after geographical areas such as NWA to indicate the origin of the North-West African desert.
Denomination
Photo credits: Wknight94 / Bruno Barral / R. Haad / Jon Taylor
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Frequency
Meteor Crater, Arizona
On Earth, approximately 78 million kilograms of extraterrestrial material fall each year. The major part is made up of dust, the micrometeorites, while the number of meteorites larger than 10 grams is estimated at 60,000 per year.
The frequency of meteorite fall depends on its mass. Thus, the larger an object, the lower the fall rate. For example, a meteorite with a mass of 100 tons, forming an impact crater of the order of 80 meters in diameter, has a frequency of fall on Earth of 100 years, while a meteorite of 100,000 tons, creating an impact crater 1 kilometer in diameter, has a fall frequency of the order of 16,000 years. Of course, since the Earth is 70% covered in water, a meteorite is more likely to fall into an ocean than into an populated area.
Age
Figures
How many are there in the world today? To what frequency they fall on Earth?
Identification
What are the characteristics that allow them to be recognized?
Location
Where are they found? Where are the craters vestiges of their arrival on Earth?
Origin
Where do they come from? How long do they wander around in interplanetary space?
