Carbonate minerals are an integral part of the carbon and water cycles, both of which are implicated in habitability, making them of particular interest in paleoenvironmental studies. In the new study, planetary scientists focused on carbon and oxygen isotope measurements of carbonate minerals detected by NASA’s Curiosity rover inside Mars’ Gale Crater.

Isotopes are versions of an element that have different masses. As the water evaporates, the lighter ones, carbon and oxygen, are more likely to escape into the atmosphere, while the heavier ones are more likely to be left behind, accumulating in larger quantities, and in this case eventually incorporated into carbonate rocks.

Scientists are interested in carbonates because they have been shown to act as climate records.

These minerals may retain traces of the environment in which they formed, such as the temperature and acidity of the water and the composition of the water and atmosphere.

“The isotopic values ​​of these carbonates indicate extreme amounts of evaporation, suggesting that these carbonates likely formed in climates where only ephemeral liquid water could exist. ‘ said Dr. David Burt, a researcher at NASA Goddard Space Flight Center.

“Our samples do not match an ancient environment in which life (biosphere) existed on the surface of Mars. However, it does not match the subterranean biosphere or the surface environment that began and ended before these carbonates formed. This does not exclude the possibility of a biosphere.

Dr. Burt and his colleagues propose two formation mechanisms for the carbonates found in Gale Crater.

In the first scenario, carbonates form through a series of dry-wet cycles within the crater.

In the second, carbonates form in extremely salty water under cold ice-forming (cryogenic) conditions inside the crater.

“These formation mechanisms represent two different climate regimes that could indicate different habitation scenarios,” said Dr. Jennifer Stern, also of NASA’s Goddard Space Flight Center.

“Wetting and drying cycles would indicate alternations between more and less habitable environments, while the extremely low temperatures in the mid-latitudes of Mars mean that most of the water is trapped in ice. “And what’s there would be very salty and unpleasant to live in.” “

These climate scenarios for ancient Mars have been previously proposed based on the presence of certain minerals, global modeling, and the identification of rock formations.

The results are the first to add isotopic evidence from rock samples to support the scenario.

The heavy isotope values of carbonates on Mars are significantly higher than carbonate minerals observed on Earth, and are the heaviest carbon and oxygen isotope values ​​ever recorded in Martian material.

In fact, both wet-dry and cold-saline climates are required to form carbonates, which are extremely rich in heavy carbon and oxygen.

“The fact that these carbon and oxygen isotope values ​​are higher than any other measured on Earth or Mars indicates that the process is extreme,” Dr. Burt 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 that made these isotope values ​​very heavy, and (ii) these heavier values ​​were conserved so that the lighter isotopes The process that generated the body value must have significantly reduced its size.””

team’s paper Published in this week’s Proceedings of the National Academy of Sciences.

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David G. Burt others. 2024. High concentrations of carbon and oxygen isotopes in carbonate-derived CO₂ At Gale Crater on Mars. PNAS 121 (42): e2321342121;doi: 10.1073/pnas.2321342121

This article is based on a press release provided by NASA.