Although the surface of Mars today is inhospitable and freezing, the NASA is looking for traces that may indicate whether, in the distant past, the Red Planet was suitable for life. Scientists, thanks to the analyzes conducted by the Curiosity rover, measured the isotopic composition of the carbonates in the Gale crater, discovering important details on the ancient Martian climate, as explained by David BurttNASA researcher:
The isotope composition in the carbonates suggests extreme evaporation. It is likely that these minerals formed in a climate that could only temporarily support liquid water.
The results of the study, published in the journal Proceedings of the National Academy of Sciencesindicate that the climate of Mars in the past was much more complex. Burtt added that the samples studied do not support a habitable surface environment, but that does not rule out a possible underground biosphere or surface life that may have existed before the formation of these carbonates.
Isotopes are variations of an element with different masses. On Mars, the evaporation process led to the accumulation of heavier isotopes of carbon and oxygen in the carbonates. These minerals, precious “climate records”, allow us to understand the environmental conditions of the time: temperature, acidity and atmospheric composition.
Two hypotheses for the formation of carbonates on Mars
The study proposes two scenarios for the formation of carbonates: one linked to cycles of humidity and dryness within Gale Crater, and the other to the presence of extremely saline water in cryogenic conditions. Jennifer Stern, co-author of the research, illustrated how wet-dry cycles could alternate between more or less habitable environments, while cryogenic temperatures would have reduced the probability of hosting life. In these conditions, in fact, the water is mainly trapped in the ice and has a high salinity, two factors that are not very favorable to life.
These climate scenarios of an ancient Mars had already been theorized previously, but this is the first time they have been confirmed by direct isotopic evidence. The values of heavy isotopes found in Martian carbonates far exceed those on Earth, indicating that an extreme evaporation process, never observed before, occurred on Mars.
To reach these conclusions, Curiosity used advanced instruments such as the Sample Analysis at Mars (SAM) and the Tunable Laser Spectrometer (TLS). The first heats the samples up to almost 900°Cwhile the second analyzes the gases released. These instruments, built by NASA’s Goddard Space Flight Center, allow the samples to be studied in detail, revealing crucial information about the Martian past.
