Curiosity’s exploration of Gale Crater on Mars has revealed new evidence of the evolution of the planet’s climate. By examining isotope values ​​of carbon-rich minerals, scientists found that ancient Mars likely experienced extreme evaporation, forming carbonates in conditions that could support only short-lived samples of liquid water.

We uncover the history of Mars’ climate

NASA’s Curiosity rover, which is currently exploring Gale Crater on Mars, is revealing new details about the planet’s ancient climate transition, from potentially hospitable to the inhospitable, barren landscape we see today, along with evidence of widespread liquid water on the surface.

Although the surface of Mars is now cold and hostile to life, NASA’s robotic explorers on Mars are investigating whether this surface could have supported life long ago. Using instruments on Curiosity, researchers measured the isotopic composition of carbon-rich minerals (carbonates) found in Gale Crater, revealing new information about dramatic changes in Mars’ ancient climate.

Climate change on ancient Mars

“The isotope values ​​of these carbonates indicate extraordinary amounts of evaporation and indicate that these carbonates likely formed in a climate that could only support transient liquid water,” said David Burtt of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. and lead author of a paper describing the study, published Oct. 7. Proceedings of the National Academy of Sciences. “Our samples are not consistent with an ancient environment where life (biosphere) existed on the surface of Mars, but this does not rule out the possibility of a subsurface or surface biosphere that began and ended before these carbonates formed.”

Isotopes are versions of an element with different masses. As water evaporated, lighter versions of carbon and oxygen became more likely to escape into the atmosphere, while heavier versions were more likely to remain, accumulate in larger quantities, and eventually incorporate into carbonate rocks. Scientists are interested in carbonates because of their proven ability to serve as climate records. These minerals can maintain properties of the environment in which they form, including the temperature and acidity of the water, as well as the composition of the water and atmosphere.

The mystery of Martian carbonates

The paper proposes two mechanisms for the formation of carbonates found in Gale. In the first scenario, carbonates form in Gale Crater through a series of wet-dry cycles. In the latter case, carbonates form in very salty water under cold ice-forming (cryogenic) conditions in Gale Crater.

“These formation mechanisms represent two different climate regimes that may represent different habitability scenarios,” said NASA Goddard’s Jennifer Stern, co-author of the paper. “While the wet-dry cycle indicates an alternation between more suitable and less habitable environments, cryogenic temperatures in the mid-latitudes of Mars indicate a less habitable environment where most of the water is trapped in ice and inaccessible to chemistry or biology, and what happens there is the end.” extremely salty and unpleasant to life.”

Isotopic Evidence and Implications for Climate

These climate scenarios for ancient Mars have previously been proposed based on the presence of certain minerals, global modeling, and description of rock formations. This result is the first to add isotopic evidence from rock samples to support the scenarios.

Heavy isotope values ​​in Martian carbonates are significantly higher than values ​​observed on Earth for carbonate minerals and are the heaviest carbon and oxygen isotope values ​​recorded for any Martian material. In fact, according to the team, both wet-dry and cold-salty climates are necessary for the formation of carbonates, which are very rich in heavy carbon and oxygen.

“The fact that these carbon and oxygen isotope values ​​are higher than other measurements on Earth or Mars suggests that the process (or processes) has been pushed to the extreme,” Burtt said. “Although evaporation causes significant changes in oxygen isotopes on Earth, the changes measured in this study were two to three orders of magnitude larger. This means two things: 1) an extraordinary degree of evaporation occurred that caused the isotopic values ​​to grow so large, and 2) these heavier values preserved, so any processes producing lighter isotopic values ​​must have been eliminated at a significantly smaller size.

Curiosity’s instruments reveal new data

This discovery was made using the Sample Analysis at Mars (SAM) and Tunable Laser Spectrometer (TLS) instruments on the Curiosity rover. SAM heats samples to approximately 1,652 degrees Fahrenheit (approximately 900°C), and TLS is then used to analyze the gases produced during the heating phase.