With its characteristic red and rough surface, Mars looks like a lifeless, dry and desolate planet; But it was not always like this. NASA’s Curiosity rover has found more evidence of an ancient salt lake that once skimmed the edges of Gale Crater about 3.7 billion years ago and may once have had tiny life forms.
The scientists, publishing their findings in the journal Nature Geoscience , analyzed the data from the Rover, identifying rocks rich in mineral salts from the Gale crater on Mars . These saline deposits represent the footprint of brine ponds that went through periods of desiccation and overflow over time (a cycle that likely repeated several times over millions of years). Those deposits therefore serve as a watermark created by climatic fluctuations as the climate of Mars changed from humid to the icy ice desert that it is today.
The next step in the research is to understand how long this transition lasted and when it happened, according to NASA’s Jet Propulsion Laboratory in Pasadena, California, in a statement.
The mysteries of Gale crater
Gale Crater is an ancient remnant of a massive impact , that is, the geological formation left over after a large impact that changed the Martian surface. Sediments carried by water and wind eventually filled the crater floor, layer by layer. After the sediment hardened, the wind carved the rock into layers, creating the mighty Mount Sharp or Aeolis Mons (which rises 5.5 km from the valley floor) and which Curiosity is climbing.
Each layer reveals a different era in Martian history and has clues to the prevailing environment at the time, which is why the work the rover is doing is so important.
“ We went to Gale Crater because it preserves this unique record of a Mars shift, ” said William Rapin of Caltech and leader of the work. “Understanding when and how the planet’s climate began to evolve is a piece of another puzzle: when and for how long was Mars able to support microbial life on the surface?”
Experts describe the salts found in a 150-meter-high section of sedimentary rock called “Sutton Island ,” which the same rover visited in 2017. The salts from Sutton Island suggest that the water was also concentrated in brine, in addition to the very dry intermittent periods that scientists had previously discovered.
Hesperian period
Satellite observations of the Red Planet certainly suggest that during this time period, known as the Hesperian period , some kind of climate transition took place. And now, the discovery of evaporated salts also indicates a shift to a more arid climate on a similar timeline.
Scientists speculate that the geological formations may have resembled salt lakes in the Altiplano of South America . Streams and rivers that flow from mountain ranges that lead to basins similar to Martian terrain. And those lakes are equally influenced by climate change.
“Finding sloped layers represents a major change, where the landscape is no longer completely underwater,” said Chris Fedo of the University of Tennessee and a co-author of the study. “The era of deep lakes may be behind us.”
We know that other examples of hypersaline lakes on Earth harbor salt-tolerant or ‘halotolerant’ biota, so after these results, the search for life in Gale Crater will undoubtedly continue.
More clues about Mars
This is the first time that a sulfate-enriched bedrock has been discovered in the crater’s sedimentary record. As such, it gives us some much-needed clues as to how Mars might have lost its water a long, long time ago.
Future missions will see Curiosity drive into earlier and earlier layers to investigate rock structures. The science team plans to stay there for the next two years to investigate these rocks. If they formed in drier conditions, that may spell a new phase of development for the crater, and reveal even more secrets about life on Mars from millions of years ago.
Referencia: An interval of high salinity in ancient Gale crater lake on Mars, Nature Geoscience (2019). DOI: 10.1038/s41561-019-0458-8 , https://www.nature.com/articles/s41561-019-0458-8
