Silica aerogel, a product widely used worldwide as an effective insulating material for energy-efficient buildings and industrial infrastructure, is being considered by researchers at Harvard University for use in "terraforming" the dead planet of Mars into one that can support human life in centuries to come.
Aerogels are considered the "world's best insulating solid material," and high-quality particulate silica aerogel represents some of the best materials in this class. They're popular as interior and exterior insulating plasters for breathable building envelopes and facades. Silica aerogels are also used in personal products, including skin and beauty care.
The top producers of silica aerogel are mostly found in the United States but a number of Chinese companies such as Guangdong Alison Hi-Tech are recognized as among the market leaders.
Researchers from Harvard, NASA's Jet Propulsion Lab, and the University of Edinburgh suggest that regions of the Martian surface could be made habitable by coating them with silica aerogel, a material that mimics Earth's atmospheric greenhouse effect.
Using modeling and experiments, researchers show that a 2 cm- to 3 cm-thick shield of silica aerogel might transmit enough visible light for photosynthesis. This layer might also block hazardous ultraviolet radiation, and raise surface temperatures permanently above the melting point of water -- all without the need for any internal heat source.
The research partners propose terraforming Mars one region at a time to ensure localized success instead of trying to terraform the entire planet all at once, which might lead to a planet-wide failure.
"This regional approach to making Mars habitable is much more achievable than global atmospheric modification," said Robin Wordsworth, assistant professor of environmental science and engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Department of Earth and Planetary Science.
"Unlike the previous ideas to make Mars habitable, this is something that can be developed and tested systematically with materials and technology we already have."
The aim of terraforming Mars bit-by-bit is to create "islands of habitability" on the Red Planet.
"Mars is the most habitable planet in our solar system besides Earth," said Laura Kerber, a research scientist at NASA's Jet Propulsion Laboratory. "But it remains a hostile world for many kinds of life. A system for creating small islands of habitability would allow us to transform Mars in a controlled and scalable way."
Researchers were inspired by a phenomenon that already occurs on Mars. Frozen CO2 on Mars' poles allows sunlight to penetrate while trapping heat. In the summer, this "solid-state greenhouse effect" creates pockets of warming under the ice.
"We started thinking about this solid-state greenhouse effect and how it could be invoked for creating habitable environments on Mars in the future," said Wordsworth. "We started thinking about what kinds of materials could minimize thermal conductivity but still transmit as much light as possible."
This is where silica aerogel comes in.
One of the most insulating materials ever created, silica aerogels are 97 percent porous. This means light moves can move through it, but the interconnecting nanolayers of silicon dioxide block infrared radiation and greatly slow the conduction of heat.
"Silica aerogel is a promising material because its effect is passive," said Kerber. "It wouldn't require large amounts of energy or maintenance of moving parts to keep an area warm over long periods of time."
Researchers have demonstrated that a thin layer of silica aerogel would increase average temperatures of mid-latitudes on Mars to like those on Earth.
"Spread across a large enough area, you wouldn't need any other technology or physics, you would just need a layer of this stuff on the surface and underneath you would have permanent liquid water," said Wordsworth.
