The planets of the solar system today seem like inhospitable terrain in which life could neither develop nor survive. Venus is surrounded by a dense atmosphere of carbon dioxide, causing a greenhouse effect that raises surface temperatures to over 400 degrees, while Mars is a frozen desert devoid of any trace of liquid water. Billions of years ago, when the solar system was young, the picture could have been very different, especially on Mars.
We know the Red Planet looked different in the past, and we recently discovered that it may be even more Earth-like than we thought. Mars originally had a magnetic field capable of repelling the strong solar wind. As its core cooled, this magnetic field disappeared and the solar wind began to slowly erode the Martian atmosphere. About four billion years later, what remains is an atmosphere about a hundred times smaller than the atmosphere surrounding Earth. As the atmospheric pressure on the surface of Mars decreased, the liquid water it contained evaporated, became part of the atmosphere, and over time was blown away by the solar wind itself.
The presence of liquid water in the Martian past is evident from the large number of traces it has left behind, such as channels excavated by the flow of rivers over millennia and millions of years, and the deltas these rivers form formed as they drained their waters into lakes and seas. greater. Today there is no liquid water on its surface, only frozen water at the poles and in the form of underground lakes, more resembling a swamp than a land lake.
More evidence for the presence of water on Mars was recently observed, which also tells us about relatively short and cyclical processes. The Curiosity rover has visited an area near Gale Crater where fissures in the terrain have been observed, indicating the existence of cycles in which the ground dries out and becomes wet again at some rate. In other words, these markings suggest that Mars may have had seasons similar to those on Earth, where lakes dry up due to lack of rain and revive when rain returns.
Thanks to the absence of plate tectonics on Mars, we can now observe the terrain as it existed billions of years ago. The discovery of these cracks in the Martian soil allows us to understand how Mars went from being a more or less hot and humid world to the cold and dry place we know today. These cracks show us the transition between these two states, when liquid water wasn’t as abundant but still had some activity.
In addition, this discovery is particularly interesting because this type of environment on Earth is particularly favorable for the emergence and development of life. These results therefore allow us to study the possible occurrence of life on Mars in the past. The presence of permanent liquid water masses on Mars is known in detail, but the environments where climate variability could alter the landscape in this way are not.
The Curiosity rover had spent years exploring terrain high in silicates, which we would expect to find at the bottom of a dry lake. It has recently advanced into a region where we find more sulfates, in a transitional area between what was once wet terrain and what has always remained dry. In addition to the change in composition, the Curiosity rover (and the science teams behind it) observed changes in the shape of the cracks seen on the ground. This would suggest that the process by which these regions dried out varied. While one eventually dried up and never refilled with water, the other underwent a cyclical process of alternating dry and wet conditions.
Here on Earth we can observe differences in the shape of cracks when a body of water dries up just once and when it dries up over time year after year. The initial cracks are T-shaped with right angles, while the cracks caused by repeating this process have larger Y-shaped angles. The latter was observed by the rover Curiosity. Additionally, the rover observed that these cracks were only a few centimeters deep, suggesting the timescale was small, days or weeks rather than thousands or millions of years as was the case when Mars lost its water entirely.
The aqueous environment is ideal for mixing different chemical compounds. As the environment dries up, these compounds exist in varying concentrations, which can favor one type of process or another. Finally, periods of drought favor the formation of polymers. When these processes occur periodically in the same place, much more complex molecules can emerge, even progenitors of life.
