We know how Mars lost its water and its habitability!

March was better before. We knew that… And we probably finally know how the red planet lost its liquid surface water, and therefore its capacity to support life. We owe this important announcement to the Curiosity rover, present on Mars since 2012, whose wheels are in very poor condition. So when you want, you can!

Curiosity has been in Gale Crater for 12 years and has traveled “only” about 32 km. It must be said that mechanics capable of carrying out repairs are quite rare on Mars, so the rover is not designed to go fast. Its objective is to take samples of Martian rock and study them on site with its scientific instruments.

The one that made this discovery possible is the SAM instrument, specially created for the analysis of carbon molecules – carbon being linked to all forms of life on Earth – which heats the samples up to 900°C. Its corollary TLS, a laser spectrometer, analyzes the gases emitted during the heating of the mineral.

Small holes, small holes, and big discoveries

It was therefore by analyzing carbonates (carbonaceous mineral) from four sites of lake-fluvial deposits on Mount Sharp (400 m altitude) that scientists noted a significant detail. Carbon is of crucial importance here, because it is linked to living things to which it is necessary (but not sufficient, carbon molecules are also present in inert matter such as rock, the tip of a pencil , etc.), but also to the climate of which it is a regulator.

“Extreme amounts of evaporation”

David Burtt of NASA's Goddard Space Flight Center, lead author of the study, said: “The isotopic values ​​of these carbonates indicate extreme amounts of evaporation, suggesting that these carbonates likely formed in a climate that could only support transient liquid water.”

“Our samples are not consistent with an ancient environment with life (biosphere) on the surface of Mars, although this does not exclude the possibility of a subsurface or surface biosphere, which began and ended before before these carbonates have formed.”

Isotopes are variants of the same chemical element depending on the number of neutrons present in the element. For example, everyone knows the famous carbon 14 which allows us to date certain samples. These carbonates were particularly enriched in carbon 13 (¹³C) and oxygen 18 (¹⁸O).

Scientists propose two formation mechanisms for these carbonates, each linked to a different climatic regime:

• First scenario: carbonates are formed following dry and wet cycles inside Gale crater.
• Second scenario: carbonates form in very salty water under cold conditions, forming cryogenic ice (CO ice² in Gale Crater.

Jennifer Stern, co-author of the article, concludes: “Evaporation can cause significant oxygen isotope changes on Earth; the changes measured in this study were two to three times greater. This means two things: 1) there was an extreme degree of evaporation that led these isotopic values ​​to be so heavy. 2) these heavier values ​​were preserved so that any processes that would create lighter isotopic values ​​had to be significantly lower in magnitude.”

In Gale Crater, water appears to have evaporated at an extreme rate. It remains of course to find out exactly when and to try to link this evaporation to an event, perhaps to the conjunction of a weakened Martian magnetic field and a solar flare powerful enough to have torn away part of the atmosphere of the red planet…

If you like splendid Martian panoramas, we recommend that you follow the account of Thomas Appéréknown for its superb raw image processing of Mars rovers.

And a little guide to Gale crater to finish: