Scientists put forward a new way to transform Mars: tile by tile.

In 1970s, NASA's pirate mission photographed Mars from orbit. (Photo: NASA /JPL)

If you want to make Mars a livable world, you don't need to spend a lot of time in the whole area of Mars.

A new study shows that humans can make many small areas on Mars livable in a relatively cheap and efficient way by placing many thin layers of silica gel on or above the surface of Mars. This kind of insulating aerogel will raise the ground temperature of Mars enough to melt water ice and block the influence of harmful ultraviolet (UV) radiation, which may create an environment where plants and other photosynthetic organisms can thrive.

Members of the research team said that we can start doing this in the near future.

Robin Wordsworth, the lead author of the research report and an associate professor of environmental science and engineering at Harvard University, said in an interview: "We should consider the goals that can be achieved within decades, not the goals that can be achieved hundreds of years later, or the goals that may never be achieved (depending on human capabilities)."

The ancient surface of Mars was very habitable. At that time, there were lakes, rivers and even oceans on the surface of Mars. But after Mars lost its global magnetic field about 4 billion years ago, the situation changed dramatically.

Charged particles from the sun began to peel off the once dense atmosphere of Mars, eventually weakening it into a thin layer, unable to keep a lot of heat or block ultraviolet radiation. Therefore, the surface of Mars becomes extremely cold and dry, and the underground aquifer of Mars becomes the only potential habitat for terrestrial life on Mars. Some researchers do agree that there may be microorganisms in the underground of Mars now. )

Many discussions about making the surface of Mars more livable focus on restoring the Martian atmosphere-for example, thickening the Martian atmosphere by evaporating a large amount of water ice and frozen carbon dioxide. However, as Wordsworth mentioned above, this "transformation" will be extremely difficult, expensive and time-consuming.

He and his colleagues may have found another way. Wordsworth said that they were inspired by observing the black spots of carbon dioxide ice sheets at the poles of Mars. These spots are considered to be the result of the "solid greenhouse effect"-sunlight passes through translucent ice and snow, warming and melting the inside of the ice and snow.

Then, Wordsworth and his team began to use silica aerogels to achieve similar effects. Silica aerogels are made up of silica clusters connected into a network on the nanometer scale. More than 97% of the volume of this material is air, so this material is widely used as an insulator in earth and space missions. For example, silicon aerogel is a common material for passive heating buildings, and NASA's Spirit and Opportunity Mars probes also rely on a thin layer of silicon aerogel to keep warm on cold nights on Mars.

The researchers placed silica aerogels in a simulated Martian environment in the laboratory and irradiated these materials with solar energy equivalent to reaching the surface of Mars. They found that an aerogel layer with a thickness of 0.8 inch to 1.2 inch (2 to 3 cm) can raise the ground temperature below by 90 degrees Fahrenheit (50 degrees Celsius). This is enough to melt the ice under the surface of Mars and keep it in a melting state, and it can even melt to several meters deep after one year. Members of the research team said that silica aerogel can also block ultraviolet rays, so it can also protect anything under it from harmful radiation.

Aerogels can be placed directly on the surface of Mars and spread on Mars like tiles. Wordsworth said it can also be used to build greenhouses for growing food crops and other plants.

Wordsworth said by email: "Extending this practice to a larger area will make the solid greenhouse effect more effective, because the proportion of heat emitted from both sides will become less, but there will still be obvious warming in the greenhouse. Whether you put this layer of aerogel on the surface or above Mars, it will not have a huge impact on the basic physical properties of this effect. "

The researchers said that this strategy can be applied to most areas of Mars. Almost anywhere between 45 degrees north latitude and 45 degrees south latitude, there is enough sunlight to produce obvious warming, and in this huge mid-latitude zone, there are many areas with abundant near-surface water ice and regular monsoon (monsoon can blow away the dust on the aerogel that blocks the sun).

Wordsworth emphasized that the new research published in the online edition of Natural Astronomy on July 15 is only the first step. If all goes according to plan, the second step will include testing this aerogel technology in places like Mars, such as the Arctic or the Atacama Desert in Chile.

Even if such a field experiment goes well, the idea will face additional challenges. For example, how should the mission deploy silica aerogels on Mars? Are these materials shipped from the earth (silica aerogels are light and easy to buy in the commercial market, so they are not expensive), or are they made of locally available materials on Mars?

Wordsworth and his team didn't solve such engineering problems. However, he said that the team has not seen any obstacles yet.

In addition, this scheme also involves some important ethical considerations. For example, should humans bring life on earth to another planet? Especially such a planet that may have its own biosphere in the past or even today?

Wordsworth said that the idea of aerogels should be less controversial than the method of comprehensively transforming Mars.

He said in an interview: "I think the advantage of adopting this partial and extensible method is that you can carefully study the areas where you are going to try this method in advance, and it is reversible."