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Colonists on Mars may have a practical option between isolated glass domes and terraforming the whole planet. A new proposal suggests a way large areas of the Red Planet might be made warm, with an atmosphere resembling Earth's, while the rest is left in its pristine state.
The idea of making Mars a second home has been popularized in science fiction and explored by planetary scientists. Releasing frozen carbon dioxide stored at the Martian poles would create a greenhouse effect that would warm the planet, releasing more CO2, and ultimately other gases.
Unfortunately, however, the latest research suggests there simply isn't enough material stored in solid form on Mars to create an atmosphere we could breathe if spread across the whole world. In Nature Astronomy, a team of researchers instead propose encasing enormous areas of Mars in an actual greenhouse made from silica aerogel.
Silica aerogel has several features that make it particularly suited for the task. It blocks ultraviolet light but lets visible wavelengths through, so it would allow enough radiation to reach the Martian surface for plants to grow. Like glass in a greenhouse, it also prevents long-wavelength radiation from escaping. Meanwhile, it is so light the shield could be built on a scale unthinkable for conventional material. Laboratory testing suggests that when exposed to radiation matching Martian sunlight, 2.5 centimeters (1 inch) of aerogel can warm the area beneath by 50ºC (90ºF), close to the difference between Mars and Earth.
"This regional approach to making Mars habitable is much more achievable than global atmospheric modification," said Dr Robin Wordsworth of Harvard University in a statement. "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."
Wordsworth and co-authors got the idea from the observation that the solid carbon dioxide at the Martian poles creates pockets of warmth in summer by letting sunlight through while preventing heat from escaping, just as its gaseous equivalent has done on a planetary scale on Earth.
Aerogels are formed of interconnected nanoscale clusters surrounding pockets of gas. Being 97 percent porous, aerogel is exceptionally light, but also an excellent insulator. It's already used to insulate the rovers from the dangerous cold of the Martian night.
"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," Wordsworth said.
Science fiction's beloved habitation domes could be replaced by roofs over entire craters.
This approach would also avoid some of the ethical problems with terraforming Mars, potentially supporting millions of people, while leaving most of the planet in its pristine state.
