In the distant past, small lakes were constantly appearing and disappearing on a neighboring planet. Today it is in their sedimentary rocks that we can find traces of possible Martian life.
Modern Mars is a cold, dry desert. But in the distant past, the planet had plenty of water, and vehicles operating there find the remains of many ancient lakes. Hundreds have already been found, but even this is only a small fraction: Geological analysis has shown that thousands of parched bodies of water may persist on Mars.
"We know about 500 ancient lakes on Mars, but almost all of them are larger than 100 square kilometers," explains one of the authors of the paper, Joseph Michalski of the University of Hong Kong. - On Earth, 70 percent of the lakes are much smaller, and appear in a rather cold environment, with glaciers retreating. Spotting similar lakes on Mars with satellites is much harder, but they must exist. It looks like we have about 70 percent more Martian lakes to discover."
Michalski and his colleagues did a meta-analysis of past work on the remains of ancient bodies of water on the Red Planet. These paleo-lakes existed at different periods in the past, but most of them date back 3.5 to 4 billion years ago, the Norse era in Mars' history. At the same time, each individual lake existed for a relatively short time, for 10-100 thousand years. This suggests that during that era, the planet was relatively cold, but experienced small periods of warming and melting ice.
Geologists also note that due to weak gravity, as well as the relatively small size of the Martian soil particles, they settled rather slowly in the water. Therefore, the ancient lakes of Mars were most likely very turbid, and light could not penetrate deep enough to allow photosynthesis. If any algae lived here, they had to stay near the surface. Even so, they may have received less energy than on Earth, because Mars is farther away from the Sun and the star was dimmer a few billion years ago.
But if there was any life on Mars, it was most likely in these bodies of water. The sedimentary rocks should retain more detailed evidence of the climate of the time. Therefore, scientists consider them to be the most interesting targets for future exploration by spacecraft. Such work may also reveal many interesting things about our own planet's past: in the distant Archean, small, often drying bodies of water may have played an important role in the development of life on Earth.
