Deep crustal carbonate rocks exposed by meteor impact on Mars

摘要

The surface of Mars is cold, dry, oxidizing, acidic and inhospitable to life. Similar conditions may have persisted for billions of years, suggesting that the best place to search for habitable environments is the subsurface. One hint of habitable conditions at depth is the presence of atmospheric methane, which may have formed through hydrothermal processes in the crust in the presence of CO_2. The observation of hydrated minerals excavated by some impact craters suggests that ancient hydrothermal systems may have existed in the subsurface, but until now, none of those deposits has been linked to carbonate minerals and CO_2 -rich environments. Previous detections of carbonate minerals that could be linked to an ancient CO_2 -rich surface environment have been sparse. Here we show spectral evidence for carbonate- and phyllosilicate-bearing, layered and foliated bedrock exhumed from deep (about 6km) within the martian crust by a meteor impact. The mineral assemblage, textural properties and geologic context of the deposits indicate that these rocks are probably ancient sediments that were metamorphosed during burial by younger volcanic materials from the nearby Syrtis Major volcano. We suggest that these buried layered carbonates might be only a small part of a much more extensive ancient carbonate sedimentary record that has been buried by volcanic resurfacing and impact ejecta. Our discovery may help explain the origin of other carbonates on Mars and indicates a high-priority site for future exobiological exploration.