Mars' climate history: Harsh past revealed, life prospects dim

Currently, Mars is dry and lifeless, but numerous geological formations indicate that in the past, there were extensive bodies and courses of water on its surface. The processes that led to the planet’s current desert-like condition, however, remain largely mysterious. To better understand them, NASA scientists analyzed the isotopic composition of minerals known as carbonates found on Mars. This information was obtained using the Curiosity rover.

Studies of carbon and oxygen isotopes are crucial to understanding ongoing climatic processes. Water, when evaporating, causes lighter isotopes of these elements to move more quickly into the atmosphere while heavier isotopes remain on the planet's surface.

David Burtt, the lead author of the study published in the journal "Proceedings of the National Academy of Sciences," explains, "The isotope values of these carbonates point toward extreme amounts of evaporation, suggesting that these carbonates likely formed in a climate that could only support transient liquid water."

These findings are not optimistic for those hoping for the discovery of past life forms on Mars. Burtt explains that the results do not align with the theory of a past environment conducive to life. However, they do not rule out the possibility of underground life or a surface biosphere that appeared and disappeared before the carbonates being studied formed.

Scientists present two possible mechanisms for forming these carbonates in Gale Crater. The first scenario suggests the formation of carbonates due to cyclical environmental changes—alternating wet and dry periods. Another possibility is the formation of carbonates in very salty waters at low temperatures, which favor ice formation.

"These formation mechanisms represent two different climate regimes that may present different habitability scenarios. Wet-dry cycling would indicate alternation between more-habitable and less-habitable environments, while cryogenic temperatures in the mid-latitudes of Mars would indicate a less-habitable environment where most water is locked up in ice and not available for chemistry or biology, and what is there is extremely salty and unpleasant for life," explains Jennifer Stern, co-author of the study.

The heavy isotope values of the carbonates recorded are significantly higher than any analogous observations on Earth and are the highest recorded in Martian materials to date. Scientists note that both scenarios could have been crucial to the formation of carbonates with such isotopic composition. This discovery provides the first isotopic evidence for hypotheses that have been developed so far based on other mineral studies and computer models.

Nick Bostrom, a Swedish philosopher and professor at the University of Oxford, believes that finding life on Mars would be bad news for humanity. The more complex the form of life found there, the more valuable it would be for science, but the worse it would be for the human race. It would place our future in a not very positive light. At the same time, he notes that the discovery of traces on Mars, though very improbable, would be significant in understanding life in the universe.

Consider the implications of discovering that life had evolved independently on Mars (or some other planet in our solar system). That discovery would suggest that the emergence of life is not a very improbable event. If it happened independently twice here in our own back yard, it must surely have happened millions times across the galaxy," comments Nick Bostrom.