NASA’s indefatigable Curiosity Rover has found one of the most forceful evidence until the date of the past habitability of Mars. But also of the fragility of this habitable ecosystem.
The finding. Curiosity arrived in Mars on August 6, 2012. Covered with dust and with deteriorated wheelscontinues to put the Gale crater in which he landed. In a stretch of 89 meters of rocky strata, on the slopes of Mount Sharp, a discovery has caught the attention of scientists.
According to a study Published in Science magazineX -ray crystallography instruments and Curiosity gas analysis have detected large amounts of siderita, an iron carbonate ore, between sulfate rich rocks.
Why it is important. Although I know They had detected carbonates on Marsthis discovery is exceptional for several reasons. First, the abundance of Siderita: it reaches between 4.8 and 10.5% of the weight of three perforated samples, which have been baptized as Tapo Caparo, Ubajara and Sequoia.
Second, the purity of the siderita. It is almost pure feco3, with very little magnesium or calcium, which contrasts with other Martian carbonates. Third, its coexistence with highly soluble salts in water: calcium sulfates and magnesium sulfates. All this fits with an ancient evaporation process.
What tells us about the old Mars. The formation of this siderite implies that the Martian atmosphere contained sufficient carbon dioxide to dissolve in water and react with the rocks. When precipitating as mineral, the CO2 was kidnapped In the rocks. The Gale crater was a lake that gradually dry out over time, leaving behind these layers of different salts or minerals.
The study estimates that recent samples could house between 2.6 and 36 millibars of atmospheric CO2, up to six times the current CO2 pressure on Mars, confirming that There was once an important carbon deposit interacting with surface water, a key requirement for habitability.
An incomplete cycle. But the story does not end there. The team found evidence that part of the siderite that formed was subsequently destroyed. A close sample (nicknamed Canaima) lacked a siderite, but contained abundant iron oxyhydroxides. Samples with siderita (tapo caparo, ubajara, sequoia) also contained these oxides in variable quantities.
Researchers believe that it is due to a diagenesis process. Subsequent fluids interacted with the rocks, partially dissolving the siderite. This destruction oxidized the iron forming oxihydroxides, and released part of the CO2 previously kidnapped again to the atmosphere. This training cycle (CO2 kidnapping) and partial destruction (CO2 release) constitutes the best evidence so far of a Old carbon cycle on Mars.
However, Siderita’s persistence indicates that it was a partial and incomplete cycle: more carbon was kidnapped than was subsequently released, unlike the carbon cycle of planet Earth, which has maintained a greater balance over geological time.
A fragile habitability. The discovery reinforces the idea of a habitable primitive Mars with liquid water interacting with a CO2 rich atmosphere until The warm and wet days are over. He tells us that the planet was habitable, but also that habitability is something very fragile.
Perhaps a lesson about the climatic stability of our own planet in the face of climate change. Mars, once again, serves as a planetary laboratory to understand the evolution and fragility of the habitable worlds.
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