「经济学人」Terraforming Mars

Restoring water on Mars may be easier than you think

IF YOU WANT to live elsewhere in the solar system, Mars is the least-bad choice. These days, the planet is a frigid, poison-soaked desert. But as the dry river valleys that cross its surface suggest, things were balmy enough in the past to allow liquid water.

For decades, scientists and science-fiction authors have toyed with the idea of restoring Mars to that warmer state by “terraforming” it—changing the planet’s climate to make it friendly to Earthlings. Their proposals tend to involve heroic engineering: injecting vast quantities of greenhouse gases into the atmosphere, say, or using nuclear explosives to melt underground ice.

A paper published this week in Science Advances offers an easier method. Samaneh Ansari, a graduate student at Northwestern University, in Illinois, and her colleagues reckon that pumping engineered dust into the atmosphere could warm Mars to the point where much of the water ice that lies beneath its surface would melt, at least in the Martian summer.

The dust would be made of tiny metallic rods each around nine millionths of a metre long. That size is carefully chosen to ensure that the particles reflect heat, which would otherwise escape to space, back down to the planet’s surface. Climate models suggest that pumping 30 litres of the dust per second into the atmosphere could boost the average temperature by 30°C or more within decades.

That is a fair amount of dust. But it represents a big improvement on the state of the art. Another paper, published in 2005, investigated chlorofluorocarbons, a class of potent greenhouse gases, and concluded that hundreds of millions of tonnes would be required. Ms Ansari reckons that, in mass terms, her method is around 5,000 times more efficient.

And the paper is just a proof of concept, with plenty of room to make things more efficient still, says Edwin Kite, a planetary scientist at the University of Chicago and one of its authors. As planets go, Mars is certainly a fixer-upper. But the renovations might be a bit easier than you think.(Aug 7th 2024)

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