Scientists are now proposing a new way to warm Earth's neighbour by injecting engineered particles - similar in size to tinsel made of iron or aluminium - into the atmosphere as aerosols to trap escaping heat and scatter sunlight towards the Martian surface. The idea is to enhance Mars' natural greenhouse effect to raise its surface temperature by around 28 degrees Celsius over a period of a decade.

This alone wouldn't make Mars habitable for humans, but the scientists who developed the proposal see it as a viable first step.

“Terraforming involves changing a planet’s environment to make it more Earth-like. For Mars, warming the planet is a necessary but insufficient first step. Previous concepts have focused on releasing greenhouse gases, but they require large amounts of resources that are scarce on Mars,” said planetary scientist Edwin Kite of the University of Chicago, who led the study published in the journal Science Advances this week.

“The key elements of our paper are a novel proposal for using engineered nanoparticles to warm the Martian atmosphere, and climate modeling that shows this approach could be much more effective than previous concepts. This is important because it offers a more feasible method for changing the Martian climate, which could inform future Mars exploration strategies,” Kite added.

NASA has sent robotic rovers to explore the surface of Mars and the InSight lander to study the planet's interior. NASA's Artemis program aims to send astronauts to the surface of the Moon for the first time since 1972 in the coming years to prepare for potential future manned missions to Mars.

There are plenty of challenges for human settlements on Mars: lack of breathable oxygen, harmful ultraviolet radiation from a thin atmosphere, salty soil unsuitable for growing crops, dust storms that sometimes cover much of the planet, and more. But its frigid temperatures are a serious obstacle.

"We propose to demonstrate that the idea of ​​warming Mars is not impossible. Hopefully our findings will encourage the scientific community and the general public to explore this fascinating idea," said lead author Samaneh Ansari, a doctoral student in the Department of Electrical and Computer Engineering at Northwestern University in Illinois.

The average surface temperature of Mars is around minus 65 degrees Celsius. With a thin atmosphere, solar heat from the Martian surface easily escapes into space. The proposal is aimed at allowing liquid water to exist on the surface of Mars, where it is present in the form of ice in the polar regions and on the subsurface.

Scientists propose continuously releasing tiny rod-shaped particles — nanorods — into the atmosphere at a rate of about 8 gallons (30 liters) per second for years.

“The idea is to transport materials or better yet, transport manufacturing tools and create nanorods on this planet because iron and aluminum are abundant on the surface of Mars,” said Ansari.

Researchers are still mindful of the potential for unintended consequences when terraforming another world for human benefit. Scientists, for example, are keen to know whether Mars has ever supported life in the past—or perhaps even now, in the form of subsurface microbes.

“While nanoparticles could warm Mars, both the potential benefits and costs of this course of action are currently uncertain. For example, in the unlikely event that Martian soil contains irreversible compounds that are toxic to all organisms native to Earth, the benefits of warming Mars would be null,” Kite said.

“On the other hand, if a photosynthetic biosphere could be established on the surface of Mars, it could increase the potential for human development in the solar system. In terms of cost, if Mars has life, studying that life could bring huge benefits, ensuring strong protection for its habitat,” Kite added.