On the surface, it was just a black stone that had fallen from the sky, sold as a curiosity to a collector in 2011. But behind that dark glint lay a secret that had been buried for billions of years. Its analysis revealed much more than just its Martian origin.
A unique Martian rock discovered in the Sahara desert
A mysterious black stone that fell from the sky was discovered in 2011 in the Western Sahara desert by a group of Saharawis. Put up for sale, it was quickly acquired by an American collector in Morocco.
Long identified as a fragment of the Martian crust, it took scientists more than a decade to reveal one of its best-kept secrets.
“Black Beauty”, a time capsule from Mars
Officially named Northwest Africa 7034 (NWA 7034), this 320-gram meteorite has a unique composition among known Martian samples. It contains minerals of very different ages, some extremely old and others younger, but its structure is consistent with observations made by NASA rovers on the surface of Mars. These clues confirm that this rock was once part of the Martian crust before being torn from the Red Planet’s surface.
Recent analysis of a tiny grain of zircon extracted from the meteorite has revealed a staggering age: 4.45 billion years. This remnant dates back to the earliest stages of Martian history, long before the planet became the arid desert we know today. Unlike most Martian meteorites, which come from more recent geological periods, NWA 7034 offers us a precious window onto the conditions on the surface of Mars in its early days.
Proof of the presence of hot water on Mars
Black Beauty is also notable for its high water content, up to ten times higher than that of other known Martian meteorites. It was already known that the rock had interacted with the water present on Mars during its formation, but the use of advanced microscopy techniques has uncovered a key element: the presence of tiny inclusions of magnetite (an iron oxide), trapped in the zircon.
This discovery suggests that the zircon crystallised in a hydrothermal environment, i.e. in the presence of water at high temperature and under oxidising conditions. In addition, the magnetite is found in zones of the zircon that are unaffected by radiation, indicating that it formed at the same time as the zircon, and not as a result of subsequent geological processes.
In other words, 4.45 billion years ago, during the pre-Noachian period on Mars, hot springs already existed in the Martian crust. Black Beauty is therefore direct evidence that water was present on Mars from its earliest ages.
An environment conducive to life?
This discovery reinforces the hypothesis that, very early in its history, Mars possessed conditions favourable to the emergence of life, at least in microbial form.
The question of whether life existed on Mars or whether it could have been transported to Earth by meteorites remains unanswered for lack of tangible evidence. But the fact that a meteorite discovered in 2011 has yielded so much information demonstrates the crucial importance of the Martian samples that NASA and China plan to bring back to Earth in the coming years.
