While our warming atmosphere on Earth threatens many living things, spurring on global warming on Mars could be the key to making the planet habitable for Earthly life. And scientists think they may have identified a material that can help turn up the thermostat for parts of the Red Planet.
"Mars is the most habitable planet in our Solar System besides Earth," said planetary geologist Laura Kerber from NASA's Jet Propulsion Laboratory. "But it remains a hostile world for many kinds of life."
The main things required to make Mars life-friendly are more heat and protection from ultraviolet (UV) rays. And additional atmospheric heat of about 50 degrees Kelvin (50 Celsius; 90 Fahrenheit) is needed to warm the dry planet's surface enough to allow water to remain in its drinkable form.
Previous proposals to give Mars a fever included releasing greenhouse gases such as CO2 from the ground - basically emulating what we've inadvertently achieved here on Earth. But a study last year identified several problems to this approach.
"Our results suggest that there is not enough CO2 remaining on Mars to provide significant greenhouse warming were the gas to be put into the atmosphere; in addition, most of the CO2 gas is not accessible and could not be readily mobilised," explained cosmochemist and planetary geologist Bruce Jakosky of the University of Colorado in a NASA press statement.
"As a result, terraforming Mars is not possible using present-day technology,"
Now, however, a Martian phenomenon called a solid-state greenhouse effect has inspired another team to investigate a different approach - one that focuses on altering local pockets of Mars, rather than its entire atmosphere.
This type of localised insulation has already been detected at the Martian poles where its ice - composed of water mixed with heat-trapping CO2 - snugly contains the heat that flowed through as light, warming the area below.
It would be like a cosy transparent blanket, allowing light through (which could be used for photosynthesis by the organisms beneath), but traps heat. In fact, aerogel has one of the lowest known abilities to transfer heat; the whole thing is over 97 percent air by volume, nestled in nanoscale silica 'fibres' that also reflect UV rays.
"Silica aerogel is a promising material because its effect is passive," explained Kerber. "It wouldn't require large amounts of energy or maintenance of moving parts to keep an area warm over long periods of time."
The researchers showed that to increase the local temperature by the required 50 degrees Celsius, they would need a 2-3 cm layer of silica aerogel.
They were then able to demonstrate, by replicating the surface conditions of Mars in a lab, that this would allow water to remain liquid throughout the Martian year while also protecting anything below it from harsh UV radiation.
Rather than terraforming the whole surface of the planet, this could create pockets suitable for life as we know it.
"A system for creating small islands of habitability would allow us to transform Mars in a controlled and scalable way," Kerber summarised.
Of course, this idea is still far from being a reality, with many pieces of the puzzle still to be resolved. For example, would it even be possible to manufacture this material on Mars?
Inevitably, some scientists also believe we should be focusing more on the problems in our own atmosphere rather than trying to alter that of another planet.
But Kerber and colleagues also point out an added bonus to transforming Mars via pockets of habitat: If life already does exist on Mars, this approach to becoming its neighbour would be less likely to cause it harm than full-scale terraforming.
To put their ideas to the test, the team is now keen to try silica aerogel out in some of Earth's more challenging environments.
This study was published in Nature Astronomy.