One-third of Mars’ surface has shallow-buried water, but it is currently too cold for use by life. Proposals to warm Mars using greenhouse gases require a large mass of ingredients that are rare on the Martian surface. However, new research suggests that artificial aerosols made from materials that are readily available at Mars — for example, conductive nanorods that are around 9 micrometers long — could warm the planet over 5,000 times more effectively than the best gases.
This artist’s impression shows how Mars may have looked about 4 billion years ago. Image credit: M. Kornmesser / ESO.
Martian geoengineering frequently surfaces as a concept in science fiction.
However, real-life researchers are also exploring potential techniques to melt and release frozen subsurface water and render the Martian environment friendlier to life.
Many of these strategies involve greenhouse gas-based warming, but the planet is sparse in ingredients necessary for greenhouse gas production.
“Dry river valleys cross Mars’ once-habitable surface, but today the icy soil is too cold for Earth-derived life,” said Dr. Samaneh Ansari of Northwestern University and colleagues.
“Streams may have flowed as recently as 600,000 years ago, hinting at a planet on the cusp of habitability.”
“Many methods have been proposed to warm Mars’ surface by closing the spectral windows, centered around wavelengths 22 and 10 micrometers, through which the surface is cooled by thermal infrared radiation upwelling to space.”
“Modern Mars has a thin carbon-dioxide atmosphere that provides only 5 Kelvin greenhouse warming via absorption in the 15-micrometer band, and Mars apparently lacks enough condensed or mineralized carbon-dioxide to restore a warm climate,” they said.
“The spectral windows can be closed using artificial greenhouse gases (e.g., chloroflourocarbons), but this would require volatilizing around 100,000 megatons of fluorine, which is sparse on the Mars surface.”
“An alternative approach is suggested by natural Mars dust aerosol. Mars dust is almost all ultimately sourced from slow comminution of iron-rich minerals on the Martian surface.”
“Because of its small size (1.5-micrometer effective radius), Mars dust is lofted to high altitude (altitude of peak dust mass mixing ratio, 15 to 25 km), is always visible in the Martian sky, and is present up to over 60 km altitude.”
“Natural Mars dust aerosol lowers daytime surface temperature, but this is due to compositional and geometric specifics that can be modified in the case of engineered dust. For example, a nanorod about half as long as the wavelength of upwelling thermal infrared radiation should interact strongly with that radiation.”
In their new paper, Dr. Ansari and co-authors propose an alternate strategy to warm Mars: aerosolizing 9-micrometer-long nanorods made from available Martian iron and aluminum.
The rods are similar in size to natural Martian dust — essentially, a little smaller than glitter — and should be able to soar high when dispersed.
Meanwhile, the rods’ other properties should help them settle 10 times slower than natural dust.
The researchers evaluated their proposal using a version of the MarsWRF global climate model and another supplemental 1D model.
Their results showed these rods would amplify sunlight that reaches the Martian surface and block ground heat from escaping.
In fact, a sustained release of 30 liters of nanorods per second could warm Mars globally by more than 30 Kelvin from its baseline and cause ice melt.
After a few months, atmospheric pressure would then increase by 20%, creating the conditions to begin a feedforward loop involving the volatilization of carbon dioxide.
Notably, the nanorod process would still take centuries and would not definitively make Mars capable of supporting human life.
“Raising Martian temperature, by itself, is not sufficient to make the planet’s surface habitable for oxygenic photosynthetic life,” the scientists said.
“On the other hand, if a photosynthetic biosphere can be established on the surface of Mars, perhaps with the aid of synthetic biology, that might increase the Solar System’s capacity for human flourishing.”
The team’s work appears today in the journal Science Advances.
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Samaneh Ansari et al. 2024. Feasibility of keeping Mars warm with nanoparticles. Science Advances 10 (32); doi: 10.1126/sciadv.adn4650
