Thanks to recent observations by NASA’s Curiosity Rover, scientists think they may have finally solved the long-standing mystery of why there is a gargantuan mountain at the heart of the robot’s landing site, the Gale Crater. As announced at a recent teleconference, the NASA team now has evidence to back up the hypothesis that the crater was filled with water for millions of years, which would have gradually sculpted Mount Sharp as layers of deposited sediment built up over time. This not only has major implications for the planet’s past climate, but also suggests that water may have lingered long enough for life to have formed.

After making touchdown back in 2012, Curiosity has been slowly making its way across the Gale Crater towards the three mile (five kilometer) tall Mount Sharp, making observations along the way. The robot reached the skirt of the mountain back in September and has since been drilling and analyzing rock samples. The primary goal is to find evidence that the planet was once habitable, but scientists are also keen to investigate the origins of Mount Sharp.

It’s not uncommon to see mounds at the center of giant craters like Gale because the ground can rebound after a space rock smashes into the surface, but Mount Sharp is way too big to have formed this way. Instead, it seems that deposition in lakebeds that could have lasted for millions of years may be responsible.

^{NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS}

Evidence for this started to accumulate as the robot journeyed towards Mount Sharp. Curiosity observed banded sediments that appeared to have been deposited by ancient rivers. As the robot continued south, it became apparent that these rivers terminated in deltas and static lakes. That’s because the sediment beds were all tilted down towards the mountain, which would suggest that the water would not have been streaming downhill off Mount Sharp, which would be the case if the mountain was there when the water started to flow. Instead, it suggests that the water flowed from the crater rim, filling up an ancient lake.

^{NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS}

Analysis of the rock layers also found that they alternated between lake, river and wind deposits, suggesting that cycles of filling and evaporation existed, taking place over tens of millions of years. Subsequent erosion over hundreds of millions of years would have then gradually sculpted the deposited material, leaving the giant peak that we still see today.

^{NASA/JPL-Caltech/ESA/DLR/FU Berlin/MSSS}

In order for the lake to have been sustained for millions of years, the planet must have had a vigorous hydrological cycle, probably involving rains or snows, to keep the atmosphere humid enough. This challenges the widely held notion that Mars’ early climate was only wet during short periods after volcanic activity or space rock impacts. Furthermore, the findings could even suggest that the planet once featured a surface ocean, which would have prevented the lake from evaporating.

Scientists also thought that, alongside water, Gale could have had the “right ingredients and environment to have been able to support microbial life,” said Michael Meyer, lead scientist of the Mars Exploration Program. But they didn’t know whether the conditions lingered long enough for life to form; now, tantalizingly, it seems that water may have persisted long enough for this to be a possibility.

[Via NASA, BBC News, New Scientist, Science, Science Alert and The Verge]