Salts may explain Mars water disappearance

NASA's Curiosity rover has been exploring the Gale crater since August 2012.

It has detected salt-bearing sediments, suggesting intermittent aridity resulted in the crater's lake evaporating in stages around 3.5 billion years ago, during an era known as the Hesperian.

"We know from orbital observations during that timing Mars was changing radically, over geological times, although it still had liquid water, lakes, rivers, and also important volcanic activity it was losing its atmosphere to space," said lead author William Rapin, from the California Institute of Technology.

"We know for sure this deeply affected its climate."

Using Curiosity data, a diverse range of salts have been uncovered in situ on Mars and interpreted as indicators of ancient brines, saline waters that became more plentiful as the Martian climate went through arid cycles, researchers say in the report, published in Nature Geoscience.

This could help scientists in their understanding of how liquid water disappeared from Mars's surface, though future exploration of younger rocks is expected to reveal more answers on how it dried out.

"We're discovering a reality of climatic fluctuations, between wetter and drier periods, that informs us on the types of ions, such as sulphur, a basic ingredient for life, that were available in water running on the surface at the time, and what type of environmental change life had to cope with if it ever existed then," Mr Rapin continued.

Salts of this form and in such large quantity is not something Curiosity has seen in older rocks it has previously looked at, indicating that a period of high salinity in the crater's lake may have occurred as water evaporated.

Earlier this year, a separate group of scientists claimed rivers bigger and more powerful than those on Earth flowed on Mars later in the planet's history than previously thought.

Curiosity has made a number of observations during its time on Mars, including spikes in methane, which is usually an indicator of life.

Australian Associated Press