Why did the once warm and humid Mars become today's desert planet? So far, it has been assumed that the loss of the greenhouse gas carbon dioxide is the cause of the climate catastrophe. However, researchers are now ruling this out. Instead, they speculate about other processes.
3.6 to 3 billion years ago, Mars was similar to Earth as a warm world with water on the surface. But then our neighboring planet cooled abruptly, the water disappeared from its surface, and it became the red desert planet we know today. The loss of the greenhouse gas carbon dioxide, according to the previously accepted hypothesis, triggered the climate catastrophe. Now a team of US planetary scientists shows that this assumption cannot be reconciled with the climate history of Mars. Rather, other causes must have played a decisive role, the scientists write in the journal "Science Advances". However, the team cannot answer the question of what caused this.
Numerous dried-up riverbeds, flow tracks around craters, and even shorelines from a vast ocean testify that Mars once had a more habitable climate. Maybe then, like on Earth, life also arose on Mars. Hardy protozoa may even have survived deep in the Martian soil to this day.
But why did our neighboring planet suddenly cool down by an average of ten degrees three billion years ago? To find an answer to this question, Edwin Kite of the University of Chicago and his colleagues studied how water-influenced structures - primarily riverbeds - evolved throughout Martian history. Because there is a close connection between the changes in these structures and the development of the Martian climate.
The team analyzed this using simulations of the Martian climate. The density and the chemical composition of the atmosphere are decisive factors in the climate model of the planet - because it is the greenhouse gases that warm the planet. The researchers ran numerous simulations with different atmospheric changes - and came across a surprising finding.
Until now, most planetary researchers saw the loss of carbon dioxide as the main cause of climate change on Mars. "Unexpectedly for us, however, the analysis of the greenhouse effect within our global climate models shows that climate change was not primarily driven by carbon dioxide, but by other effects."
However, the researchers cannot derive from their models which effects these were. They see the decrease in water vapor in the atmosphere or the formation of clouds of ice crystals in the upper atmosphere as possible causes, which could have reflected a considerable proportion of the solar radiation.
In addition, greenhouse gases other than carbon dioxide may have played a role. It is also unclear whether the disappearance of water from the surface of Mars was a consequence or a contributory cause of climate change. Researchers hope that analysis of soil samples will provide more information about the red planet's climate history.