NASA's Curiosity rover has found important clues about its ancient atmosphere on Mars. The research team discovered signs of siderite (a carbonate iron mineral) by analyzing samples collected by Curiosity from different locations on Mount Sharp in Gale Crater. This discovery provides direct evidence that carbon cycling existed on ancient Mars, providing a new perspective for understanding the climate conditions on Mars. The relevant paper was published in the latest issue of the journal Science. Scientists have long believed that in order to support the existence of liquid water, Mars needs a thicker atmosphere than it does now, especially containing more carbon dioxide (CO2) to maintain warmth. However, although previous studies have detected the presence of carbonates, their quantity is much lower than expected. This time, the discovery of Curiosity explains this contradiction. A team from the University of Calgary in Canada analyzed rock samples from four different stratigraphic units using data collected by Curiosity between 2022 and 2023. These samples represent the transition from the bottom of the lake to a wind eroded environment, and their mineral composition was analyzed using an X-ray diffractometer on a rover. The team was surprised to find that the formation rich in magnesium sulfate contains high concentrations of siderite, with a content of over 5% to 10% by weight. This discovery was unexpected, as previous orbital probes had not found carbonates in such formations. Based on the source and chemical properties of siderite, the team speculates that it was formed through reactions between water and rocks, as well as through evaporation processes. This indicates that at some point in the history of Mars, CO2 was chemically locked into sedimentary rocks. If such minerals are widely distributed in areas rich in sulfates, Mars may contain a previously undiscovered massive carbon reservoir. In addition, some carbonates were later destroyed, meaning that some CO2 returned to the atmosphere, forming a carbon cycle. This discovery provides important clues for people to understand how Mars transformed from a warm and humid planet to today's cold and dry world. At the same time, this also means that future exploration of other sulfate rich regions on Mars will help people better understand the early history of Mars and the changes in its atmosphere, bringing us one step closer to the goal of fully unraveling the mystery of Mars. (New Society)