Measurements taken by the Curiosity rover are providing clues to scientists about how Mars’ ancient climate has transformed.
He rover Curiosity of NASA, currently engaged in the exploration of Gale Crater on Marteis providing new clues as to how the ancient Martian climate does is transformed from potentially suitable for life (with evidence of widespread liquid water on the surface) to a surface inhospitable to terrestrial life and became uninhabitable as we know it today. Although the surface of Mars is frigid and hostile to life today, NASA’s robotic Mars explorers are searching for clues into the distant past. Researchers used instruments aboard Curiosity to measure the isotopic composition of carbon-rich minerals (carbonates) findsti in Gale Crater and discovered new insights into how the Red Planet’s ancient climate transformed.
New climate scenarios
“The isotope values of these carbonates indicate extreme amounts of evaporation, which suggests 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, in Maryland, and lead author of a paper describing this research published Oct. 7 in the Proceedings of the National Academy of Sciences. “Our samples are not consistent with an ancient environment with life (biosphere) on, although this does not rule out the possibility of a subsurface biosphere or a surface biosphere that began and ended before these carbonates formed.”
Isotopes are versions of an element with different masses. As water evaporated, the light versions of carbon and oxygen were more likely to escape into the atmosphere, while the heavy versions were left behind more often, accumulating in greater abundances and, in this case, eventually leaving. Scientists are interested in carbonates because of their proven ability to serve as climate records. These minerals may retain signatures of the environments in which they formed, including the temperature and acidity of the water, and the composition of the water and atmosphere.
The paper proposes two formation mechanisms for the carbonates found at . In the first scenario, carbonates form through a series of wet-dry cycles within Gale Crater. In the second, carbonates form in very salty water under cold, ice-forming (cryogenic) conditions in Gale Crater.
“These formation mechanisms represent two different climate regimes that could present different habitability scenarios,” said Jennifer Stern of NASA Goddard, a co-author of the paper. “The wet-dry cycle would indicate alternation between more and less habitable environments, while cryogenic temperatures in the mid-latitudes of Mars would indicate a less habitable environment in which most of the water is unavailable for chemistry or biology, and what is there is extremely salty and unpleasant to life.”
A high evaporation rate
These climate scenarios for ancient Mars, 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 to support the scenarios.
Heavy isotope values in Martian carbonates are significantly higher than those 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 cold-salt and cold-salt carbonates are necessary to form carbonates so rich in heavy carbon and oxygen.
“The fact that these carbon and oxygen isotope values are higher than anything else measured on Earth or Mars indicates that a process (or processes) has been taken to the extreme,” Burtt said. “While evaporation can cause significant changes in oxygen isotopes on Earth, the changes measured in this study were two to three times larger. This means two things: 1) there was an extreme degree of evaporation that led these isotope values to be so heavy, and 2) these heavier values were preserved, so any process that would have created lighter isotope values must have been significantly smaller in terms of magnitude.”
This discovery was made using the Sample Analysis at Mars (SAM) and Tunable Laser Spectrometer (TLS) instruments aboard the Curiosity rover. SAM up to almost 900°C and then TLS is used to analyze the gases that are produced during that heating phase.
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