The idea of terraforming Mars and making its atmosphere and environment more Earth-like for human settlement has been around for decades. During that time, many proposed methods have been considered and then discarded because they were “too expensive” or required technology far beyond what we have today. Nevertheless, the idea has persisted and is often considered as part of long-term plans for establishing a human presence on Mars. Given the many plans to build human outposts on the Moon and then use that infrastructure for missions to Mars, opportunities for terraforming may be closer than we think.
Unfortunately, any plans to terraform Mars are fraught with unresolved obstacles, not least of which are the cost, distance, and the need for technologies that do not currently exist. To trigger a greenhouse effect and warm the surface of Mars would require enormous amounts of greenhouse gases, which would be very difficult and expensive to transport. However, a team of engineers and geophysicists led by the University of Chicago have proposed a new method of terraforming Mars using nanoparticles. This method would use the resources already present on the Martian surface and, according to their feasibility study, would be sufficient to start the terraforming process.
The team was led by Samaneh Ansari, a postdoctoral fellow in the Department of Electrical and Computer Engineering (ECE) at Northwestern University. She was joined by Edwin Kite, assistant professor of geophysical sciences at the University of Chicago; Ramses Ramirez, assistant professor in the Department of Physics at the University of Central Florida; Liam J. Steele, a former postdoctoral fellow at UChicago, now at the European Center for Medium-Range Weather Forecasts (ECMWF); and Hooman Mohseni, professor of ECE at Northwestern (and Ansari's postdoctoral fellow).
As described in previous articles, the process of terraforming Mars consists of a few steps, all of which complement each other. That is, progress in one area will inevitably have a positive impact on another. These steps include:
- Warming of the planet
- Compression of the atmosphere
- Melting the water ice
Warming the planet would cause the polar ice caps and permafrost to melt, releasing liquid water onto the surface and into the atmosphere as vapor. The large amounts of dry ice in both ice caps (particularly in the Southern Hemisphere) would also be released, thickening and further warming the atmosphere. As Robert Zubrin argues in The Case for Mars, this would result in an atmospheric pressure (atm) of about 300 millibars (30% of Earth's atm at sea level), which would allow humans to stand outside on the surface without a pressure suit (though they would still need warm clothing and bottled oxygen).
Previous proposals for terraforming Mars have recommended achieving the first step by inducing a greenhouse effect, specifically by introducing additional greenhouse gases. Examples include additional carbon dioxide, methane, ammonia, and chlorofluorocarbons, which would either have to be mined on Mars or imported from Earth (or Venus, Titan, and the outer solar system). Unfortunately, these options would require a fleet of spacecraft making round-trip flights to Mars, Venus, or the outer solar system, and/or extensive mining operations on Mars.
In contrast, Ansari and her colleagues' proposal involves using man-made dust particles made from local minerals*. Thanks to missions like Curiosity and Perseverance, which have taken numerous rock and soil samples for analysis, we know that dust grains on Mars are rich in iron and aluminum. If these particles are shaped into conductive nanorods about 9 micrometers long – the width of a very thin human hair – and arranged in different configurations, they could be released into the atmosphere, where they would absorb and scatter sunlight.
Image taken by the Viking 1 orbiter in June 1976. It shows the thin atmosphere and dusty, red surface of Mars. Image credit: NASA/Viking 1
To determine the extent to which these particles would affect the Martian atmosphere, the team ran simulations using Northwestern University's Quest high-performance computing cluster and the University of Chicago Research Computing Center's (RCC) Midway 2 computing cluster. Based on a 10-year particle lifetime, two climate models were simulated that constantly ejected 30 liters (7.9 gallons) of nanoparticles per second into the atmosphere. Their results suggest that this process would warm Mars by more than 30 °C (86 °F), enough to trigger melting of the polar ice caps.
Through their simulations, the team found that their method is over 5,000 times more efficient than previous proposals for inducing a greenhouse effect on Mars. In addition, the increase in average temperature would make the Martian environment more favorable for microbial life, which is crucial for plans to ecologically transform Mars. By introducing photosynthetic bacteria (such as cyanobacteria), atmospheric carbon dioxide could be slowly converted into oxygen gas. This is precisely how oxygen became an integral part of the Earth's atmosphere 3.5 billion years ago.
As Kite suggested in a UChicago News article, this method would still take decades, but would be logistically simpler and much cheaper than current plans to terraform Mars:
“This suggests that the barrier to warming Mars to the point where liquid water can form is not as high as previously thought. It would still take millions of tons to warm the planet, but that is five thousand times less than previous proposals to warm Mars globally. This greatly increases the feasibility of the project. This suggests that the barrier to warming Mars to the point where liquid water can form is not as high as previously thought.”
Of course, much research still needs to be done before such a method can be field tested on Mars. Last but not least, the question of how the particles are affected by atmospheric changes on Mars is still unclear. Currently, Mars has cloud formation and precipitation in the form of dry ice that condenses in the atmosphere and falls back to the surface as CO2 snow. Once the polar ice caps have melted, Mars could experience more cloud cover and precipitation with water that could condense around the particles, causing them to fall back to the surface in the form of raindrops.
This artist's impression shows what Mars might have looked like about four billion years ago, when much of its surface was covered with liquid water. Image credit: ESO/M. Kornmesser
This and other potential climate feedback mechanisms could lead to a variety of problems. But one of the best aspects of this proposed method is its reversibility. One simply needs to stop producing and releasing particles into the atmosphere and the warming effect will end over time. Moreover, the focus of the study only extends to warming the atmosphere to the extent that microbial life can live there and eventually grow food crops. Still, this study offers terraforming enthusiasts a viable and less expensive way to get the whole process of “greening Mars” rolling. Kite said:
“Climate feedbacks are really hard to model accurately. To do something like this, we would need more data from both Mars and Earth, and we would need to proceed slowly and reversibly to ensure the effects work as intended. This research opens new avenues for exploration and potentially brings us one step closer to the long-held dream of a sustainable human presence on Mars.”
As the saying goes, “a journey of a thousand miles begins with a single step.” In this case, the first step may be the most difficult, comparable only to the challenges of sustaining changes to Mars' climate in the long term. By providing future generations with a viable and (comparatively) inexpensive option, we could make the dream of making Mars habitable for terrestrial life a reality!
*This process is known as In-Situ Resource Utilization (ISRU) and is an important part of the architecture of NASA's Moon-Mars mission and other plans to establish a permanent human presence on the Moon and Mars in the coming decades.
Further reading: News from the University of Chicago, Nature Advances
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