Evidence of Mars’s Ancient Watery Past Found in Mineral

A mineral called siderite, discovered in abundance within rock samples extracted by a NASA rover on Mars, presents compelling evidence that the planet once had a warmer, wetter environment. This environment potentially featured significant bodies of water and the possibility of sustaining life.

The Curiosity rover, which touched down on Mars in 2012 with the primary goal of determining whether the planet could have once supported microbial life, identified the mineral in rock specimens taken from three different locations within the Gale crater between 2022 and 2023. Gale crater is a vast impact basin characterized by a central mountain.

Siderite is an iron carbonate mineral. Its discovery in ancient sedimentary rocks, dating back billions of years, suggests that Mars once possessed a substantial atmosphere rich in carbon dioxide. This gas would have acted as a greenhouse agent, raising the planet’s temperature to a level where liquid water could exist on the surface.

Many scientists believe that certain features of the Martian landscape suggest that liquid water previously flowed across the surface, potentially forming oceans, lakes, and rivers that could have served as habitats for ancient microbial life.

Similar to Earth and Venus, carbon dioxide serves as the main climate-regulating greenhouse gas on Mars. It effectively traps heat from the sun within the atmosphere, leading to a warmer climate.

Previously, there was limited evidence indicating that the Martian atmosphere was once abundant in carbon dioxide.

The prevailing theory suggests that the atmosphere transitioned from a dense, carbon dioxide-rich state to a thinner, carbon dioxide-depleted state, for reasons not entirely understood. During this shift, geochemical processes caused carbon to become trapped within rocks in the planet’s crust in the form of carbonate minerals.

The samples acquired by Curiosity, obtained by drilling approximately 1.2 to 1.6 inches (3-4 centimeters) into the rock to analyze its chemical and mineral composition, reinforce this hypothesis. The analyses showed the samples contained up to 10.5% siderite by weight, as measured by an instrument aboard the six-wheeled rover.

According to Benjamin Tutolo, a geochemist from the University of Calgary and a participating scientist on NASA’s Mars Science Laboratory Curiosity rover team, one of the longstanding puzzles in the study of Martian planetary evolution and habitability revolves around the scarcity of carbonate mineral detections on the Martian surface, considering the presumed requirement of large quantities of carbon dioxide to warm the planet and maintain liquid water.

Tutolo, who is also the lead author of the study published in the journal Science, noted that models predict carbonate minerals should be widespread. However, rover-based investigations and satellite-based orbital surveys of the Martian surface have yielded little evidence of their presence to date.

Because rock similar to that sampled by the rover has been found globally on Mars, the researchers believe it too contains an abundance of carbonate minerals and may hold a substantial portion of the carbon dioxide that once warmed Mars.

The sedimentary rocks within the Gale crater, including sandstones and mudstones, are believed to have been deposited around 3.5 billion years ago, when the area was occupied by a lake and prior to the significant climatic shift on Mars.

Planetary scientist Edwin Kite from the University of Chicago and Astera Institute, a co-author of the study, stated that the transformation of Mars’s surface from a more habitable state in the past to its current apparently sterile condition represents the most significant known environmental catastrophe.

Kite also added that they do not know the cause of this change, but Mars has a very thin carbon dioxide atmosphere today, and there is evidence that the atmosphere was thicker in the past. Discovering a major unsuspected deposit of carbon-rich materials is an important new clue and understanding where the carbon went is crucial.

The rover’s discoveries shed light on the carbon cycle that existed on ancient Mars.

On Earth, volcanoes release carbon dioxide into the atmosphere, which is then absorbed by surface waters, primarily the ocean, and combines with elements like calcium to form limestone rock. Through plate tectonics, this rock undergoes reheating, eventually releasing the carbon back into the atmosphere through volcanic activity. However, Mars lacks plate tectonics.

Tutolo emphasized that the key aspect of the ancient Martian carbon cycle highlighted in their study is its imbalance. Specifically, it appears that significantly more carbon dioxide was sequestered into rocks than was subsequently released back into the atmosphere.

He also stated that Models of Martian climate evolution can now incorporate their new analyses, and in turn, help to refine the role of this imbalanced carbon cycle in maintaining, and ultimately losing, habitability over Mars’ planetary history.