In September 2022, a group of nomadic meteorite hunters discovered a pink stone in the Sahara Desert in the West African nation of Mali. The names of the finders – presumably local Bedouins or Tuareg – remained anonymous. The rare find finally ended up at NASA via a detour. It quickly became apparent that the stone was a meteorite from Mars with a unique chemical composition.
At first, no one knew how old the meteorite called Teghaza 001 really was. Now his age has been determined. The results were published in the specialist magazine “Science”. For researchers, a window opens into the early geological development of Mars and, in particular, its water.
There are no global shifts in tectonic plates on Mars, which is why its surface allows direct insights into past geological ages of its development. Most Martian meteorites found on Earth are very young – a few hundred million years old. They come from geologically new regions of Mars, such as the Tharsis region, where the gigantic Olympus Mons is located, which is about three times as high as Mount Everest on Earth. However, there are hardly any samples from the much older southern plateaus - and therefore little knowledge about the early history of the red planet.
In the laboratory, the researchers now determined the exact composition of the stone. They first looked at the decay of radioactive isotopes in the rock to estimate its age. They found three lead compounds that are suitable for this age determination.
All three indicated that the meteorite was formed 4.1 billion years ago. At this point, Mars was in its earliest geological epoch. Teghaza 001 is one of the oldest known finds from Mars. Only the famous piece “Black Beauty” (NWA 7034) and ALH 84001 are comparable.
The minerals in the rock also showed changes that were due to reactions with a resource that would also have been necessary for early life on Mars: water. Evidence of this was provided by rich traces of sodium found in the two minerals. Sodium dissolves particularly well in water and, thanks to the high chemical reactivity of water, can also penetrate into cooled magma rocks.
In another study, the scientists looked even more closely at tiny phosphate crystals in the stone that had chemically bound water. Inside they found traces of two completely different water supplies. The first comes from the interior of Mars itself: water that rose with the magma from the Earth's interior and contained comparatively little deuterium - a heavy variant of hydrogen that is naturally found in water. The second supply was significantly richer in deuterium and entered the stone from the outside: it was water from the Martian crust that had previously been in contact with the Martian atmosphere on the surface.
The fact that this surface water contained twice as much deuterium as Earth's seawater today 4.1 billion years ago is an important finding for planetary researchers: It shows that Mars had already lost a large part of its water in its first hundred million years. At that time, light hydrogen atoms quickly escaped into space because the weak gravity of Mars could not hold them - what was left behind was an increasingly heavy, deuterium-rich residual water. Teghaza 001 provides the oldest direct evidence to date of how early Mars began to dry out.
"It wasn't until we looked closer that we realized how unique this meteorite really is," said study lead author Yang Liu of NASA's Jet Propulsion Laboratory in Southern California. “One of the study’s reviewers called it the Rosetta Stone for Mars.”
The researchers suspect that a later impact from a celestial body catapulted the stone from the crust of Mars into space. The rock on the surface of Mars was subjected to enormous pressure, which is only reached at a depth of 5,000 meters in the upper mantle, and heated to up to 1,200 degrees Celsius. This is indicated by highly compressed reidite and maskelynite components.
Based on its age and composition, researchers believe the Teghaza 001 meteorite came from the Noachian southern highlands of Mars. The crust in this area represents the oldest geological epoch on the red planet and, in contrast to the flat, young lowlands of the north, is pockmarked by meteorite impacts.
Mars is a mystery in many ways. It is similar to Earth in many ways, and yet several factors appear to have prevented life from flourishing on it.
Mars research is far from complete. For a long time it was believed that Mars had not been volcanically active since ancient times. This is how Olympus Mons was formed in the northern hemisphere around 3.5 billion years ago. But recent satellite images show lava flows on its slopes that are barely two million years old.
A study recently appeared in the specialist magazine “Science Advances” that describes evidence of gas leaks – and thus volcanic activity – at Alba Mons. Although it is flatter than Olympus Mons, it is as large as the USA.
A huge flat plain, the Amazonian Plain, stretches between the two megavolcanoes. An ancient ocean could have extended there until three billion years ago.
By the way: The water on Mars has not completely disappeared. Since the 1970s, an 1,800-kilometer-long, tube-shaped cloud of water vapor has been observed every morning in spring and summer, which disappears again around midday. This occurs because the morning sun melts thin layers of frost on the Martian soil and strong easterly winds drive the rising water vapor up the slopes of Arsia Mons. This is made possible by the extremely thin but still measurable atmosphere on the red planet.
