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Mars Attacks. His A breath of atmosphere means that if you were on the surface, it would be a race to see if suffocation or sub-zero temperature killed you first. But maybe it's a bit too big for the red planet. It's not all a rusty and frozen hellish landscape. In mid-latitudes, a few inches from the ground, you'll find ice – frozen gases like carbon dioxide or even frozen water.
If only Mars were warmer, more humid, more oxygenated, the so-called Martians groan. If only people did not have to take home bubbles to colonize Mars and make manifest the destiny of humanity among the stars, or something like that. While most humans are busy making the Earth less habitable, some humans propose to make Mars more similar to Earth, via a process called terraforming.
Carl Sagan had launched this idea in 1971 and he already knew that the main problem would be the Gossamer atmosphere. It lets too much ultraviolet rays and too much infrared – it's heat – to turn Mars ice into hospital water. Either the planet has already lost all its insulating CO2, or it is bottled underground one way or another. On Earth, the greenhouse effect is about to blossom; on Mars, he escaped. And yet: "Sunlight entering the snowpack a few inches from the surface can cause large increases in temperature, leading to sublimation," says Robin Wordsworth, scientist in planetary science at Harvard. The frozen CO2 turns into gas and the geysers come out of the ground. This is what is called a solid state greenhouse effect: the light penetrates the surface, crosses the translucent ice, then hits the darker, warmer regolith. Thus, Wordsworth, who studies the climate, evolution and potential habitability of other worlds, wonders: can you do it artificially? Could an insulating material create a greenhouse effect in the solid state hot enough to make Mars habitable? "If you wanted to take an atmosphere and reduce it to a few inches, what would you need?" Asks Wordsworth. "The key is the transparency of the material, the propagation of light and its thermal insulation."
In a new paper in Nature AstronomyWordsworth proposes a candidate: silica airgel. As you can recall, it is the "solid smoke" used by the Stardust probe to capture dirt in space, a nanocrystalline matrix of air essentially composed of silicon oxide and whose thermal conductivity is extremely low. That is, it is a sufficient insulator for spacecraft.
It's also translucent. The intelligent molecular structure of silica airgel passes photons from visible and infrared light with sufficient efficiency to visibly increase the temperature. But the ultraviolet, at the wavelengths that would sunburn a human and at the wavelengths that break his human DNA, bounces from the outside as a private part, and no so-called "ultraviolet" is on the list.
Wordsworth has not yet tested the idea on Mars, of course. His team did it in a lab, assembling airgel particles and tiles in a polystyrene box, then projecting attenuated light to approach the Martian spectrum and flux. The result? A temperature rise of 50 K – it's almost 360 ° F. "The fact that it is smoky means that it diffuses light, but that most of the light passes through," says Wordsworth . "A perfectly transparent airgel, you would reach the point where you could get hundreds and hundreds of K of warming. The limit is on the science of materials, not on the basic theory. "
Then they introduced their temperature change measurements into a computer model that included the Martian regolith – "with the Martian seasonal cycle, atmospheric pressure and the rest to extrapolate our results," says Wordsworth. And the numbers indicate that under the airgel layers, the Martian soil would warm up quickly enough to allow the presence of liquid water. According to Wordsworth, given the presence of other essential nutrients, a limited area under the airgel, perhaps slightly under pressure, could even sustain life. "The main question is whether you want to grow biomass or crops," he says. "If it's the last case, then something more like a greenhouse would make more sense. If you do something like pushing algae to the surface, it could literally be a surface layer. "
Perhaps the most important is that warming is fast, much faster than hundreds or even thousands of years, either to release CO2 on Mars (if it exists) or to synthesize and emit greenhouse gases. super greenhouse. On the other hand, says Chris McKay, NASA's astrogeophysicist and expert on Mars, the effect would necessarily be local. This is not terraforming. "Maybe they could cover a size the size of the Midwest County," says McKay. "The only way to create a greenhouse on an entire planet is to use gases in the atmosphere. As we know on Earth, it's an effective way to warm up a planet. "
Last year, researchers published an analysis of Mars data suggesting that the planet had lost most of its CO2, which was no longer enough to cause a natural warming of the greenhouse. One of the authors of this article claims that Wordsworth's idea, even if it is only feasible on a small scale, is worth testing. "I would imagine that there would be questions about how this would work in practice," says Bruce Jakosky, scientist in planetary sciences at the University of Colorado. "Would the decanted dust from the atmosphere eliminate the effect? Would the airgel be strong enough to withstand the real world environment on Mars? But these are issues that can be addressed. "
Wordsworth says that small scale is actually an advantage in terraforming. "You can choose areas where you are convinced there is no life to fear," he says. Nevertheless, you must do it where there is water ice, which leaves room for the possibility of extrophiles. "Ethical considerations must be taken into account, but they are much more controllable than if you were trying to do something global."
The really cool part, though? This is testable on Earth first, with Mars analogues such as the Atacama Desert or the McMurdo Dry Valleys in Antarctica. This is the next step: try an airgel sheet on Dry Valley gravel to see if the soil warms up and the ice melts. And if it is, it may be the next step: Mars.
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