Source: The Guardian

For future astronauts bound for Mars it will surely rank as a positive: when they sit down to dinner on the barren red planet, they should at least have plenty of greens.

The harsh environment on Mars has always made growing food a daunting prospect, but scientists believe they have cracked the problem with sheets of material that can transform the cold, arid surface into land fit for farming.

The “aerogel” sheets work by mimicking Earth’s greenhouse effect, where energy from the sun is trapped on the planet by carbon dioxide and other gases. Spread out in the right places on Mars, the sheets would warm the ground and melt enough subsurface ice to keep plants alive.

Robin Wordsworth, who worked on the sheets at Harvard University, said: “If we want to make sustainable habitats on another planet using present-day technology, this approach could be very useful. It’s completely scalable, so the area covered could be anywhere from a few square metres to large regions of the planet.”

Should humans ever decide to spread beyond Earth, as the late Stephen Hawking declared we must, then growing food on alien worlds will be a skill that has to be mastered. But on Mars the conditions are hardly conducive. The planet is frigid and dry and bombarded by radiation, the soil contains potentially toxic chemicals and the wispy atmosphere is low on nitrogen.

In the past, scientists and science fiction writers have proposed “terraforming” barren worlds, an approach that calls for the whole atmosphere to be rebuilt. In 1971 the American astronomer Carl Sagan suggested that vaporising the northern polar ice cap on Mars might release enough water into the atmosphere to do the trick. More modest ideas have involved erecting greenhouses instead.

The aerogel sheets do not solve all of the problems but they could help future spacefarers create fertile oases on desolate planets where plants and other photosynthesising organisms can take root. Because life would only grow beneath the sheets, the risk of contaminating the rest of Mars with foreign lifeforms would be minimal, Wordsworth said.

The aerogel used to make the sheets is composed 97% of air, with the rest made up of a light silica network. The researchers, including scientists at Nasa and the University of Edinburgh, showed that 2cm- to 3cm-thick sheets of silica aerogel blocked harmful UV rays, allowed visible light through for photosynthesis and trapped enough heat to melt frozen water locked in Martian soil.

“Placing silica aerogel shields over sufficiently ice-rich regions of the Martian surface could therefore allow photosynthetic life to survive there with minimal subsequent intervention,” the researchers wrote in Nature Astronomy. The sheets could be laid directly on the ground to grow algae and aquatic plants, or suspended to provide room for land plants to grow beneath them.

Wordsworth said: “The best place to try this is similar to where you’d want to land humans: at mid-latitudes where sunlight levels are still relatively high, but where it’s close enough to the polar caps that near-surface ice deposits are still scattered around.

“You can imagine this being used in a number of ways. The most achievable in the short term would be a small-scale test with a robotic lander. In the longer term it could be used in support of human exploration missions, and eventually to produce long-lived habitats that you would aim to make as self-sustaining as possible.”