Evrim Yazgin
Cosmos science journalist
NASA’s Curiosity rover has found new details in Mars’s Gale crater which helps explain how the Red Planet went from one with a climate with liquid water to the inhospitable place it is today.
It may help scientists determine if there ever was life on Mars.
Evidence gained by rovers on Mars makes the pretty clear case that, at one point in the ancient past, Mars had liquid water on its surface. And liquid water, it turns out, was pretty widespread on the planet.
Liquid water is considered a prerequisite for the existence of life. It is certainly necessary for any plans for humans to colonise other planets.
But the wet period on Mars is believed to have ended about 3 billion years ago.
Today, Mars is frigid and inhospitable.
A new study published in the Proceedings of the National Academy of Sciences uses data from Curiosity’s instruments to measure the composition of the Martian soil. The researchers focused on the different isotopes of atoms in carbon-rich minerals.
Isotopes are atoms with the same number of protons, but different numbers of neutrons. They share the same chemical properties but can have different physical properties such as radioactivity.
“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,” says lead author David Burtt of NASA’s Goddard Space Flight Center.
Burtt says this result puts a dent in the prospect of finding evidence of past life on the Martian surface, even in its ancient history.
“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.”
Carbonates are proven to act as a climate record. They retain signatures – in the form of isotope abundances – of temperature, water acidity, and the composition of water and atmosphere.
The results from Gale crater present two formation mechanisms for the carbonates.
Either they formed through a series of wet-dry cycles, or they formed in very salty water under cold, icy conditions.
“These formation mechanisms represent two different climate regimes that may present different habitability scenarios,” says co-author Jennifer Stern of NASA Goddard. “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.”
