Tissint, a Moroccan meteorite
It was only in the nineteenth century that it was accepted that meteorites were really pebbles falling from the sky. Today we know that these are the keys to understanding the origin of the Solar system and the planets. It has even been discovered that some of them came from La Luna and others from Mars, but since they are very rare, it is believed that a kilogram is worth at least ten times the price of gold.
Despite this rarity, we know something about Martian meteorites. We learn their origin mainly because of the gases they contain, whose isotopic composition is identical to that of the Martian atmosphere, as measured by the lander Vikin and its successors. However, since no mission has yet returned samples of the Red Planet, exobiologists and cosmochemists attach great importance to the discovery of these meteorites on Earth, especially if people have witnessed their fall. The later their arrival on Earth, the lower the risk of decontamination by terrestrial living organisms, and therefore it is easy to show that any traces of life are of Martian origin.
We remember, for example, the case of the Allan Hills meteorite 84001 (ALH84001), which was presented in 1996 as a possible proof of the appearance of the devi form on Marsila about 4 billion years ago.
Two fragments of the Tissint meteorite.
Found in 1984 in the Allans Hills, the hills at the end of the trans-Antarctic Chain in Victoria, it fell to Earth long before this date. Although electron microscopic observations revealed shapes resembling those of bacteria, they could well have been ground-based contaminants. Currently, these tracks are generally not considered as evidence of lavie on Mars, but we don’t despair of finding them in later meteorites.
A young Martian igneous rock.
We understand why a meteorite that arrived on Earth on July 18, 2011, near the village of Tissint in Morocco, may excite researchers. The fragments, recovered three months later by the nomads, were too fresh to remain in the desert for long; therefore, they must have been part of a small celestial body that woke the inhabitants of the region with supersonic booms around 2 am.
A fragment of the Tissint meteorite.
The analysis finally showed that it was indeed a Martian meteorite, more precisely an unhergottite, that is, a representative of one of the three great classes of Martian meteorites. These classes are named after the villages near which people witnessed their fall. Thus, the fall was observed near the French village of Chassigny in 1815, that at Shergoti in India (1865) and at Nakhla in Egypt (1911).
Another fragment of the Martian meteorite Tissint.
Shergottites are gabbro-basaltic rocks that are thought to date back to the unmachachaud crystallization on Mars from 150 to 500 million years ago. If so, these must be Lacroix Martian fragments torn from its gravity by the fall of unaster in the newly geologically active regions of the Red Planet. So they probably came from Tharsis, the plateau where, among other things, Mount Olympus, the largest volcano in the Solar System, is located.