Terraforming Mars: Modeling engineered aerosols to warm the planet
Whenever humans arrive on Mars, they’re going to find it a difficult place to exist. Mars is cold, with an average surface temperature of -55°C; temperatures can plunge to -125°C with dust storms lasting months; its atmosphere is very thin and almost all carbon dioxide; and all the water is frozen and mixed with ice made of CO2. Oh, and solar radiation will be hazardous on Mars’ surface since the planet has no ozone layer to block ultraviolet radiation, especially so during solar flares. Disneyland it is not.
The debate over terraforming Mars
New Martians will need to live underground until, someday, maybe, Mars can be terraformed to, if not quite looking like Earth, at least a planet more hospitable to fragile human creatures.
There are arguments for and against terraforming Mars. If humans do terraform, one of the first suggestions is to increase Mars’ greenhouse effect by melting the CO2-ice caps.
Elon Musk proposed the use of continuous, low-fallout nuclear explosions to simulate artificial suns, but a 2018 paper criticized the idea as only being able to raise Mars’ greenhouse effect from its natural 5°C at 6 millibars pressure to at most 20 mbar with a 10°C boost to surface temperature. That’s not enough to get to the 30°C or more warmup needed to have stable liquid water on the surface.
Engineered aerosols as an alternative
In recent years, new methods have been put forth that could warm Mars in other ways, including the release of aerosols that create an IR (infrared radiation) forcing that would warm the surface. But so far, the models analyzing this scenario have been simplistic—they assumed any aerosols released would have a static, unchanging distribution instead of including the movement and dynamical behavior of these engineered aerosols.
In the journal Geophysical Research Letters, a group of researchers from the US, the UK and Brazil have now modeled the release into the Martian atmosphere by plume tracking, finding strong radiative‐dynamical feedbacks. They found that the particles lofted locally and carried globally, and these feedbacks could enable engineered‐aerosol warming.
The two cases considered were the release of graphene disks, about 250 nm in diameter, and the release of aluminum rods about 8 microns long and 60 nm in diameter. Both absorb and scatter thermal infrared radiation rising from the planet’s surface.
How the aerosol model behaves
While neither choice was optimized for warming (so their results do not represent an upper limit on heating), the engineered aerosols considered have, by design, a much stronger interaction with thermal IR than with sunlight. Their group’s model, led by Mark I. Richardson of Aeolis Research in Chandler, Arizona in the United States, found that a single, continuous source of aerosols (they modeled 0 to 60 liters per second) would stably saturate globally in less than 4 Martian years (7.5 Earth years).
They also included a time‐varying background of natural dust, which also interacts radiatively, from an observational database corresponding to a relatively storm-free period on the planet.
Using their global 3-dimensional model, the team presented, among other results, the time evolution of the global average surface temperature for a 3 liter per second release of the IR-active aluminum particles starting at the planet’s northern equinox and continuing for 5 Mars years, followed by an increase to 60 L/s. (In fact, the timescale of the response was found to be almost independent of the release rate.)
After about 8 Mars years, the surface temperature jumped drastically from 3–4°C to about 25°C above the unperturbed temperature of Mars, and at about 15 years the temperature stabilized at about 35°C warming. This should be enough to allow liquid water on the Martian surface.
Source: phys.org
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Terraforming Mars: Modeling engineered aerosols to warm the planet