Earth is not an isolated object , but is open to outer space. It is estimated that between 70 and 100 tons per day of extraterrestrial material reach our planet in the form of cosmic dust . A continuous shower of minerals from different sources, mainly asteroidal and cometary types. It could be said that we are exposed to a faint cosmic rain that goes unnoticed. However, sometimes this is not the case and we are witnessing much more spectacular events.
Occasionally, a larger object enters our atmosphere and undergoes an ablation process that, fortunately for us, fragments the meteoroid, sometimes generating very bright meteors, the striking fireballs, which when they explode in the atmosphere are called technically racing cars. Meteorites should not be talked about until the fragments of the meteoroid hit the Earth’s surface.
But why are meteorites important? Could they bring something dangerous? Are we exposed to a large impact? Obviously, the answer to all these questions requires more detail than a short article like this one. However, we can give a general informative veneer. Responding simultaneously to the first and the last question, we could say that meteorites play a constructive and destructive role.
Constructive because they are equivalent to planetesimals (solid objects formed by dust, rock and other materials from space that cannot be observed) from which the Earth and other planets and moons were formed and because they could contribute to the origin of life, as carriers of water and fundamental inorganic and organic compounds. Destructive, because in addition to recent events such as Chelyabinsk, the study of the Earth’s geological record confirms that large impacts have occurred, generating craters of even hundreds of kilometers in diameter with important geobiological implications.
The composition of meteorites is varied, and can be broadly classified into three groups: rocky, rocky-metallic and metallic . Most of them come from asteroids, although a small group comes from the Moon and Mars. So far, nothing has been detected that could pose a risk to humanity , although this matter is taken into account in the research protocols that are part of the so-called “Planetary Protection”.
The recommendations of the main international organizations indicate that meteorites should be considered, due to their scientific importance, a world heritage site. Specifically in Spain, the largest known meteorite fell in Molina de Segura (Murcia) and all of them have been part, since 2007, of our geological heritage.
Jesús Martínez-Frías (@J_MartinezFrias) is a Researcher at the Institute of Geosciences, IGEO (CSIC-UCM), Director of the Spanish Network of Planetology and Astrobiology (REDESPA) and Member of the NASA-MSL, ESA-ExoMars and NASA-Mars missions -2020
