NASA's Curiosity rover has found important clues about its ancient atmosphere on Mars. The research team discovered signs of siderite, a kind of iron carbonate mineral, by analyzing samples collected by Curiosity from different sites in Mount Sharp, Gail Crater. The discovery provides direct evidence that there was a carbon cycle on ancient Mars, providing a new perspective on understanding the climate conditions of Mars. Related papers are published in the latest issue of Science magazine.

  Scientists have long believed that to support the existence of liquid water, Mars needs a thicker atmosphere than it is now, especially with more carbon dioxide (CO2) to keep warm. However, although previous studies have detected the presence of carbonate, its quantity is much lower than expected. This time, the discovery of the "Curiosity" explains this contradiction.

  The University of Calgary team in Canada analyzed rock samples from four different stratigraphic units using data collected by the Curiosity between 2022 and 2023. These samples represent the transition from the lake bottom to the wind-eroded environment and their mineral composition is analyzed by an X-ray diffractometer on the rover. The team was surprised to find that the high concentration of siderite contained in the magnesium sulfate-rich formation, and its content reached more than 5%-10% by weight. This discovery was unexpected because previous orbital detectors did not find carbonate in such formations.

  Based on the source and chemical properties of siderite, the team speculated that it was formed through the reaction between water and rock and the evaporation process. This suggests that at some time in Mars' history, CO2 was chemically locked into sedimentary rocks. If such mineral distributions are widely present in sulfate-rich regions, Mars may contain a huge carbon reservoir that has not been discovered before. In addition, some carbonates were later destroyed, meaning that some of the CO2 returned to the atmosphere, forming a carbon cycle.

  This discovery provides important clues to understanding how Mars has transformed from a warm and humid planet to a cold and dry world today. At the same time, this also means that the future exploration of other sulfate-rich regions on Mars will help people better understand the early history of Mars and the changes in the atmosphere, and will be one step closer to the goal of fully solving the mystery of Mars. (Reporter Zhang Mengran)

[Editor in charge: Zhou Jingjie]