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Humans have been fascinated by Mars probably since the first of their species turned their eyes to the night sky. Space exploration today bears witness to this continuing fascination.
Since the 1960s, more than 40 missions have attempted to reach the red planet. As a result, three rovers are active on the surface of Mars, plus one lander and one helicopter, while eight orbiters circle the planet.
Simulating the red planet’s geology and hydrology can reveal how the landscape has changed, helping the search for landing sites for future missions.
“Many of the planets and moons in our solar system are very interesting, but Mars is a bit special,” said François Forget, a climate scientist at Sorbonne University in France. “Today, Mars is quite similar to Earth, but in the past — 3 to 4 billion years ago — it was even more similar.
While the extensive exploration so far has produced a wealth of geological data, much remains unknown about the fourth planet from the Sun.
There are signs of a once-vast ocean covering the northern hemisphere of Mars, but elsewhere scars carved by rivers and glaciers.
Yet the climate process that shaped the planet seen today remains a mystery.
As far back as 4 billion years ago, when life began to appear on Earth, there were rivers and lakes of liquid water on Mars. This raises the possibility that life has also evolved on Mars.
But scientists are also interested in the processes that created the dry desert planet seen today and what they might reveal about Earth’s climate.
Areas on the surface of Mars are more than 3 billion years old. Such records are not available on Earth, which has been fundamentally altered by life, which has consumed much of the planet’s early history.
Something else also makes Mars special: it’s a place where astronauts hope to go at some point.
The European Space Agency, or ESA, and the US National Aeronautics and Space Administration – NASA – are working to send astronauts to Mars.
Forget is the principal investigator of an EU-funded project developing a model of how Mars evolved in an attempt to answer some questions about the planet’s history.
The project, known as Mars Through Time, began in late 2019 and is scheduled to last through most of 2025.
Current climate models for Mars cover only a short period — a few years — of its history, and simulating effects such as glaciers, rivers and lakes is difficult, especially over long periods of time, according to Forget.
The project’s model is designed to run for thousands or even millions of years, simulating the past evolution of geological features along with a changing atmosphere.
While current climate models require assumptions about where water sat on the planet’s surface, the evolution for Mars is designed to calculate where water would have naturally evolved and reached a stable equilibrium, Forget says.
This is done by incorporating more details into the model such as microclimate effects.
For example, poleward slopes of a planet are usually colder, which could lead to the formation of ice and glaciers. On warmer slopes facing the equator, liquid water may be more likely.
“If you wanted to model the Earth but you didn’t know anything about it, you would put water in the ocean and slowly the Earth’s evolution model would, for example, build up Antarctica,” Forget said. “You want to be able to do the same thing on Mars, and of course the model will create lakes, oceans and rivers.”
It also includes large-scale changes that occur over longer geologic time scales. The tilt of Mars’ axis of rotation, known as the obliquity, typically changes every 50,000 years, resulting in large-scale climate changes.
Carbon dioxide glaciers
To use the model, the scientists rely on known data from Mars’ past, such as geology and topography, the location of rivers, lakes and glaciers, and the composition of the atmosphere. They also make some assumptions about missing data.
As the simulation runs, the scientists adjust their assumptions and parameters until the evolution of the Mars model matches the existing knowledge of the planet in the past and present.
When a model matches geological records, it provides information about the planet’s environment, chemistry and atmosphere and how they changed, according to Forget.
So far, the model has confirmed that some odd-looking bogs – debris left behind by glaciers – are likely made of frozen carbon dioxide.
The simulations have also indicated how these CO2 glaciers could have formed and shown to have caused dramatic changes in the composition of the Martian atmosphere.
To test one theory of how liquid water might have existed on the Martian surface, the researchers plugged a hydrogen-rich parameter into their model to get a possible clue as to how the Martian climate might have gotten warm enough to sustain liquid lakes and rivers.
The model showed that if Mars had previously had a hydrogen-rich atmosphere, it could have caused a significant greenhouse effect and increased the planet’s temperature.
At the other end of the temperature scale, a better understanding of how glaciers form and where frozen water might exist today could help a manned mission to Mars.
“Having access, without too much difficulty, to water ice on Mars will be very useful, according to NASA,” Forget said. “They have set up project teams that look at where water ice is found, and the Mars Through Time project can really contribute.
EU research could also provide information on where liquid water might be found. As it happens, these are areas where astronauts don’t want to land.
That’s because of a concept called planetary protection. The last thing astronauts want to do is contaminate Mars with microbes from Earth, especially liquid water where they could thrive.
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