Carbonate minerals are of particular interest in paleoenvironmental research as they are an integral part of the carbon and water cycles, both of which are relevant to habitability. In new research, planetary scientists focused on carbon and oxygen isotope measurements of carbonate minerals detected by NASA’s Curiosity rover within the Gale crater on Mars.
An artist’s concept of an early Mars with liquid water (blue areas) on its surface. Image credit: NASA / MAVEN / Lunar and Planetary Institute.
Isotopes are versions of an element with different masses. As water evaporated, light versions of carbon and oxygen were more likely to escape into the atmosphere, while the heavy versions were left behind more often, accumulating into higher abundances and, in this case, eventually being incorporated into the carbonate rocks.
Scientists are interested in carbonates because of their proven ability to act as climate records.
These minerals can retain signatures of the environments in which they formed, including the temperature and acidity of the water, and the composition of the water and the atmosphere.
“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,” said Dr. David Burtt, a researcher at NASA’s Goddard Space Flight Center.
“Our samples are not consistent with an ancient environment with life (biosphere) on the surface of Mars, although this does not rule out the possibility of an underground biosphere or a surface biosphere that began and ended before these carbonates formed.”
Dr. Burtt and his colleagues propose two formation mechanisms for carbonates found at Gale crater.
In the first scenario, carbonates are formed through a series of wet-dry cycles within the crater.
In the second, carbonates are formed in very salty water under cold, ice-forming (cryogenic) conditions in the crater.
“These formation mechanisms represent two different climate regimes that may present different habitability scenarios,” said Dr. Jennifer Stern, also from NASA’s Goddard Space Flight Center.
“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.”
These climate scenarios for ancient Mars have been proposed before, based on the presence of certain minerals, global-scale modeling, and the identification of rock formations.
This result is the first to add isotopic evidence from rock samples in support of the scenarios.
The heavy isotope values in the Martian carbonates are significantly higher than what’s seen on Earth for carbonate minerals and are the heaviest carbon and oxygen isotope values recorded for any Mars materials.
In fact, both the wet-dry and the cold-salty climates are required to form carbonates that are so enriched in heavy carbon and oxygen.
“The fact that these carbon and oxygen isotope values are higher than anything else measured on Earth or Mars points towards a process (or processes) being taken to an extreme,” Dr. Burtt said.
“While evaporation can cause significant oxygen isotope changes on Earth, the changes measured in this study were two to three times larger.”
“This means two things: (i) there was an extreme degree of evaporation driving these isotope values to be so heavy, and (ii) these heavier values were preserved so any processes that would create lighter isotope values must have been significantly smaller in magnitude.”
The team’s paper was published this week in the Proceedings of the National Academy of Sciences.
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David G. Burtt et al. 2024. Highly enriched carbon and oxygen isotopes in carbonate-derived CO2 at Gale crater, Mars. PNAS 121 (42): e2321342121; doi: 10.1073/pnas.2321342121
This article is based on a press-release provided by NASA.
Source : Breaking Science News