The current Martian surface seems far removed from any form of life. Yet, new data suggests that billions of years ago, the red planet may have offered a much more hospitable environment. Curiosity, NASA's rover, continues to provide crucial clues about this dramatic transformation.
Within Gale Crater, the robot is exploring carbon-rich minerals that reveal a radically different ancient climate. Isotopic analyses point to extreme evaporations, indicating that liquid water could have existed, but intermittently.
Artist's rendering of Mars with vast stretches of liquid water on its surface.
Credit: NASA/MAVEN/The Lunar and Planetary Institute
Measurements taken from the carbonate minerals in Gale Crater reveal that these rocks were formed under two possible climatic scenarios. In one, wet and dry cycles alternated, creating fluctuating conditions between environments more or less conducive to life. The other hypothesis suggests formation under cryogenic conditions, with very salty water and freezing temperatures, which would be less favorable to life.
David Burtt, from NASA's Goddard Space Flight Center, explains that the heavier isotopes found in these minerals are evidence of highly intense evaporation processes. Indeed, on Mars, these isotopes are significantly heavier than those measured on Earth in similar formations. This suggests that the water underwent massive evaporation, an extreme phenomenon that left its mark on the rocks in the crater.
Carbonates are natural archives of climate evolution. They hold information about temperature conditions, water acidity, and atmospheric composition. Thanks to the instruments onboard Curiosity, such as the Tunable Laser Spectrometer (TLS) and the Sample Analysis at Mars (SAM), scientists can look back in time and decode these ancient environments.
Jennifer Stern, also from the Goddard Space Flight Center, notes that the alternation of wet and dry periods could suggest that Mars was intermittently habitable. On the other hand, a cold and salty climate would be much less favorable to life, as the water would be trapped in ice.
The isotopic values recorded on Mars represent record levels, never before observed elsewhere in the solar system. This could mean that the processes that formed these rocks were driven to their extremes on the red planet.
These new discoveries reinforce the idea that Mars underwent significant climate transformations. They provide additional isotopic evidence to better understand how the planet transitioned from a wet environment to a barren desert.
What is an isotope and why is it important in understanding Mars?
An isotope is a version of a chemical element that has the same number of protons but a different number of neutrons. This means they have different masses. For example, carbon has several isotopes, including carbon-12, carbon-13, and the well-known carbon-14.
These mass variations allow isotopes to act as indicators of environmental conditions. When a natural process, such as the evaporation of water, occurs, the lighter isotopes tend to escape, while the heavier ones remain.
On Mars, the analysis of isotopes in minerals like carbonates helps scientists decipher ancient climates. Heavier isotopes found in Martian rocks indicate extreme evaporation, providing clues about past conditions.
The study of isotopes is thus crucial for understanding whether Mars may have, at some point, harbored liquid water, or even life, before becoming the dry and cold desert it is today.