Curiosity rover provides new insights into how Mars became uninhabitable

NASA’s Curiosity spacecraft, which is currently exploring Mars’ Gale Crater, is exploring how the ancient Martian climate evolved from potentially life-friendly to terrestrial life as we know it. provides new details about how the Earth’s surface has become uninhabitable. that.

Mars’ surface is currently frigid and inhospitable to life, but NASA’s Mars robotic probes are searching for clues about whether life may have existed in the distant past. Researchers will use instruments on board Curiosity to measure the isotopic composition of carbon-rich minerals (carbonates) found in Gale Crater to determine how Mars’ ancient climate changed. discovered new insights about

“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 David Burt of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the book. A paper describing the research was published in the Proceedings of the National Academy of Sciences.

“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. does not exclude the possibility of a biosphere.

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.

This paper proposes two formation mechanisms for the carbonates found in Gale. In the first scenario, carbonates form within Gale Crater through a series of wetting-drying cycles. In the second, carbonates form in extremely salty water under cold ice-forming (cryogenic) conditions within Gale Crater.

“These formation mechanisms represent two different climate regimes that may present different habitability scenarios,” said study co-author Jennifer Stern of NASA Goddard. “Wetting and drying cycles would indicate alternations between more and less habitable environments, but the extremely low temperatures in the mid-latitudes of Mars mean that most of the water is trapped in ice. “It would represent an inhospitable environment, unusable for chemistry or biology,” and what is there would be very salty and unpleasant to life. ”

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, the researchers say both wet-dry and cold-saline climates are needed 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 processes are at an extreme,” Burt said. 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: 1) to an extreme degree; 2) These heavy values ​​were conserved, so the processes that produced the lighter isotopic values ​​were much smaller in magnitude. It must be,” he continued.

The discovery was made using the Sample Analysis of Mars (SAM) and Tunable Laser Spectrometer (TLS) instruments aboard the Curiosity rover. SAM heats the sample to nearly 1,652 degrees Fahrenheit (nearly 900°C) and uses TLS to analyze the gases produced during that heating step.