NASA’s Curiosity rover, which is currently studying Gale crater on Mars, is uncovering fresh insights into how the planet’s ancient climate transitioned from one that may have supported life—showing signs of extensive liquid water on the surface—to one that is now barren and unfit for life as we know it.
Despite Mars’ chilly and life-inhibiting surface today, NASA’s robotic missions are probing for evidence that suggests the planet could have hosted life in its distant past. Using advanced instruments aboard Curiosity, researchers analyzed the isotopic makeup of carbon-rich minerals (known as carbonates) collected in Gale crater, revealing significant information about the climatic shifts on the Red Planet.
David Burtt from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a paper detailing this research published on October 7 in the Proceedings of the National Academy of Sciences, stated, “The isotope readings from these carbonates indicate considerable evaporation, implying that they likely formed in conditions that could only briefly support liquid water.” He further noted, “Our samples do not align with an ancient environment that hosted life on the surface of Mars, although this does not exclude the chance of life existing underground or on the surface before these carbonates were formed.”
Isotopes are variations of an element that possess different masses. During evaporation, lighter isotopes of carbon and oxygen tend to escape into the atmosphere more readily, leaving heavier isotopes behind. This results in higher concentrations of the heavier forms being stored in carbonate rocks. Scientists focus on carbonates due to their ability to preserve climate records, capturing data about their formation conditions—such as water temperature, acidity, and the chemical makeup of the environment.
The paper outlines two potential ways the carbonates in Gale crater could have formed. The first suggests that they developed during multiple wet-dry cycles, while the second postulates their formation in extremely saline water under cold, ice-generating conditions.
Co-author Jennifer Stern from NASA Goddard explained, “These two mechanisms represent distinct climatic regimes that might offer different scenarios for habitability. Wet-dry cycles would signify a fluctuation between environments that were more and less hospitable to life, whereas cryogenic conditions at Mars’ mid-latitudes would indicate a primarily inhospitable environment where water is mostly trapped in ice, with any available water being very salty and unlikely to support life.”
Prior theories about ancient Martian climates have stemmed from the identification of specific minerals, large-scale modeling, and recognizable rock formations. This study is the first to present isotopic evidence supporting these theories drawn from actual rock samples.
The heavy isotope ratios observed in Martian carbonates are remarkably higher than those found in Earth’s carbonate minerals, marking the highest isotope values recorded in any materials from Mars. According to the research team, both wet-dry and cold-salty conditions must have contributed to the formation of such heavily enriched carbonates.
Burtt remarked, “These elevated carbon and oxygen isotope values surpass anything documented on Earth or Mars, indicating a process (or processes) taken to extremes.” He pointed out that while evaporation alters oxygen isotopes significantly on Earth, the isotopic variations noted in this study were two to three times greater. This indicates that an extreme level of evaporation was responsible for these heavy isotope readings, and that any processes leading to lighter isotope values were likely much less intense.
This fascinating discovery was made possible through the Sample Analysis at Mars (SAM) and Tunable Laser Spectrometer (TLS) tools mounted on the Curiosity rover. The SAM device heats samples to nearly 1,652 degrees Fahrenheit (almost 900°C), and the TLS analyzes the gases generated during this heating process.
The research was financed by NASA’s Mars Exploration Program as part of the Mars Science Laboratory project. The Curiosity rover was developed by NASA’s Jet Propulsion Laboratory (JPL), managed by Caltech in Pasadena, California. JPL oversees the mission for NASA’s Science Mission Directorate in Washington. The SAM instrument, a compact scientific lab consisting of three different chemistry-analysis tools, including the TLS, was designed and built by NASA Goddard.
