A Material Way for Making Mars Habitable
Editorials News | Jul-18-2019
New research suggests that regions of the Martian surface could be made habitable with a material, the silica airgel, which mimics the Earth's atmospheric greenhouse effect. With the help of modeling and experiments, the researchers show that a 2- to 3-centimeter-thick silica airgel shield could transmit enough visible light for photosynthesis, block dangerous ultraviolet radiation, and raise temperatures below the melting point of water permanently, all without the need for any internal heat source.
People have dreamed for a long time with the remodeling of the Martian climate to make it habitable for humans. Carl Sagan was the first outside the field of science fiction to propose terraforming. In a 1971 article, Sagan suggested that the vaporization of the ice sheets of the North Pole "would produce ~ 10 sg cm-2 of atmosphere on the planet, higher global temperatures through the greenhouse effect and a much greater likelihood of liquid water".
Sagan's work inspired other researchers and futurists to take the idea of terraforming seriously. The key question was: are there enough greenhouse gases and water on Mars to increase your atmospheric pressure to levels similar to those on Earth?
In 2018, a pair of researchers funded by NASA from the University of Colorado, Boulder and the University of Northern Arizona found that processing all available sources on Mars would only increase atmospheric pressure to approximately 7 percent of the Earth.
Terraforming Mars, apparently, was an impossible dream to fulfill.
Now, researchers at Harvard University, NASA's Jet Propulsion Laboratory and the University of Edinburgh have a new idea. Instead of trying to change the whole planet, what would happen if it adopted a more regional approach?
The researchers suggest that regions of the Martian surface could be made habitable with a material, the silica airgel, which mimics the Earth's atmospheric greenhouse effect. With the help of modeling and experiments, the researchers show that a shield of silica airgel two to three centimeters thick could transmit enough visible light for photosynthesis, block dangerous ultraviolet radiation and raise temperatures below the melting point of the water permanently, all without the need for any internal heat source.
The article is published in Nature Astronomy.
"This regional approach for making Mars habitable is much more feasible than global atmospheric modification," said Robin Wordsworth, Assistant Professor of Environmental Science and Engineering at the John A. Paulson School of Engineering and Applied Sciences at Harvard and the Department of the earth and planetary science. "Unlike previous ideas to make Mars habitable, this is something that can be systematically developed and tested with the materials and technology we already have."
"Mars is the most habitable planet in our Solar System, in addition to Earth," said Laura Kerber, Scientific Investigator of NASA's Jet Propulsion Laboratory. "But it is still a hostile world for many types of life; a system to create small islands of habitability would allow us to transform Mars in a controlled and scalable way."
The researchers were inspired by a phenomenon that already occurs on Mars.
Unlike Earth's polar ice caps, which are made of frozen water, the polar ice caps on Mars are a combination of ice water and frozen CO2. Like its gaseous form, frozen CO2 allows sunlight to penetrate while it traps heat. In the summer, this solid-state greenhouse effect creates hot spots under the ice.
"We started thinking about this solid-state greenhouse effect and how it could be invoked to create habitable environments on Mars in the future," Wordsworth said. "We started thinking about what kind of materials could minimize thermal conductivity but still transmit as much light as possible."
The researchers landed on silica airgel, one of the most insulating materials ever created.
Silica aerogels are 97 percent porous, which means that light moves through the material, but the interconnected nano layers of the infrared radiation of silicon dioxide significantly reduce heat conduction. These aerogels are used in several engineering applications today, including NASA's Mars Rovers.
"Silica airgel is a promising material because its effect is passive," Kerber said. "It would not require large amounts of energy or maintenance of moving parts to keep a hot area for long periods of time."
Utilizing models and experiments which mimicked the Martian surface, the researchers showed that a thin layer of this material increased the average temperatures of mid-latitudes on Mars at temperatures similar to Earth.
"Distributed in a large enough area, you would not need any other technology or physics, you would only need a layer of these things on the surface and below you would have permanent liquid water," Wordsworth said.
By: Preeti Narula
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