Mars Nanorods Could Warm the Red Planet 5,000 Times More Efficiently

Warming Mars with metallic nanorods

Establishing permanent human colonies on Mars would require major changes. The Red Planet is far from the Solar System’s most welcoming environment, and its present conditions are poorly suited to survival.

Its climate is among the greatest obstacles. Mars is far too cold for warm-blooded humans, with a median temperature of -64 degrees Celsius (-85 Fahrenheit). Any effort to terraform the planet would therefore need to raise its temperature.

Scientists have now identified a possible way to achieve this, claiming that their approach is 5,000 times more efficient than other proposed methods.

A team headed by electrical engineer Samaneh Ansari at Northwestern University in the US suggests that Mars could be heated - and kept warm - by releasing nanoscale metal rods into its atmosphere, where they would generate and sustain a greenhouse effect.

"You'd still need millions of tons to warm the planet, but that's five thousand times less than you would need with previous proposals to globally warm Mars. This significantly increases the feasibility of the project," says geophysicist Edwin Kite of the University of Chicago, corresponding author on the research.

"This suggests that the barrier to warming Mars to allow liquid water is not as high as previously thought."

Why greenhouse warming is difficult on Mars

The greenhouse effect is the most practical known means of warming a planet. Yet, despite Earth’s experience, creating one is more challenging than it may appear. Earlier proposals to heat Mars through a greenhouse effect have relied on greenhouse gases, including those that warm Earth and Venus.

On Earth, greenhouse warming has proved all too easy. The atmosphere fills with gases such as carbon dioxide and methane, which scatter heat emitted by the surface, slowing its escape into space and increasing temperatures.

Under previous proposals, filling Mars’s thin atmosphere with these greenhouse gases would create the same warming effect, lifting Martian temperatures to a point at which photosynthetic organisms could survive.

The difficulty is that Mars lacks much of the material needed for such a plan. It would be necessary either to transport vast quantities from Earth or extract them from beneath the Martian surface. Both options would be costly and difficult.

But what if Mars’s readily available resources could be used instead? Rover observations have established that its surface soil contains abundant metallic minerals, including aluminium and iron. Could minute, shimmering metal particles be fired into the Martian atmosphere like a glitter cannon, where they would remain aloft and trap sunlight in the same way as carbon emissions on Earth?

Mars nanorods could retain atmospheric heat

Ansari and her colleagues modelled tiny metal rods, comparable in size to dust particles already found on Mars and slightly smaller than commercial glitter. With an aspect ratio of 60:1, these nanorods would be released into the Martian sky. The researchers calculated the heat that glittering clouds of metallic nanorods could retain, as well as the amount of dust needed to create and maintain a greenhouse effect.

Their size and form would allow the nanorod dust to remain suspended above Mars for 10 times longer than natural dust. Released continuously at 30 litres per second, the nanorods could produce the proposed warming effect, melting surface ice and increasing atmospheric pressure as carbon dioxide ice sublimates.

Over centuries, atmospheric pressure would keep rising as carbon dioxide ice caps at the poles volatilised.

This would still fall far short of making Mars habitable. Its atmosphere would remain too low in oxygen to breathe. However, after the surface became hospitable to bacteria, microbes could be introduced to begin the lengthy and difficult process of producing oxygen.

The nanorod approach would also require considerable time - several decades - but could eventually warm Mars by more than 28 degrees Celsius. This would move its climate into a range that remained uncomfortable for vertebrates, yet warm enough for photosynthetic microbial life: an important first step towards a terraformed Mars.

There are, however, issues still to be addressed. It is uncertain how long the nanorods would stay in the Martian atmosphere, which continues to leak into space. This is not unusual, as every atmosphere leaks, but Mars lacks the global magnetic field that helps contain Earth’s atmosphere.

As Mars warmed, the nanoparticles might also attract water particles, as dust does in Earth’s atmosphere, before returning to the surface as rain. They may therefore not remain airborne for as long as desired. This is a potential obstacle that cannot yet be predicted reliably and will need additional study.

Nevertheless, "This research opens new avenues for exploration and potentially brings us one step closer to the long-held dream of establishing a sustainable human presence on Mars," Kite says.

The research has been published in Science Advances.