Firing Moondust Into Space to Create Sun Shield Could Combat Climate Change

Firing dust from the moon into space to create a sun shield could be a "feasible" way to mitigate global warming on Earth, a team of scientists has found.

In a study published in the journal PLOS Climate on Wednesday, researchers explored seemingly outlandish astro-engineering approaches to combat climate change and examined how they could work in practice.

The researchers came from the University of Utah (UU) and the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.

"Dust is efficient at scattering starlight—a small amount of dust by mass may deflect much more light than a full-grown planet," Benjamin Bromley, a researcher at UU's Department of Physics and Astronomy and lead author of the study, told Newsweek.

"The seed of the idea for this research was to ask, how much dust would be needed to reduce the sunlight received here on Earth? We dove in from there."

Atmospheric concentrations of greenhouse gases have been rising significantly since the Industrial Revolution. It is a trend driven by human activities such as the burning of fossil fuels. The changing composition of the atmosphere is leading to increased entrapment of solar energy, resulting in a warming world.

One group of strategies that has been proposed to combat climate change includes ambitious concepts designed to reduce the amount of solar energy the Earth receives. This could balance the heat trapped by the increasing amount of greenhouse gases in the atmosphere.

Scientists have considered various ideas for solar shields. These include vast swarms of tiny, guidable satellites; redirected asteroids; and placing clouds of dust at special orbital locations.

The approaches explored in the PLOS study fall into the latter camp. Potential sources of dust include mines on Earth, the moon or even near-Earth asteroids.

One dust-cloud solution that the researchers examined would involve delivering moondust to a way station. It would be situated at a special orbital location called the Lagrange L1 point, a gravitational sweet spot between Earth and the sun, around 1 million miles away from our planet.

A natural or man-made object at L1 is able to "hover" in the same position relative to the sun and Earth while orbiting our star. Essentially, the gravitational forces at L1 would enable the station to move right along with the Earth, directly between our planet and the sun. Dust could be ejected from a spacecraft there to create a cloud that would act as a sun shade.

But after exploring different possibilities, the authors said that one novel approach was the most promising. This method involves shooting dust from the moon in a jet—what they call a "moonjet"—toward L1. The path of the moonjet would be designed to provide as much shade as possible.

These streams of moondust could shade Earth for up to a week, the authors found. Bromley said this moonjet approach was more "feasible" than the others that were considered.

"The moonjet concept is less efficient than other approaches, but it is simpler and might be easier to sustain—the idea would be to autonomously mine dust from the moon's surface, bringing it to a launch platform or platforms," Bromley said.

The launchers could be electromagnetic, like a rail gun, powered by a bank of solar panels. Rail guns are devices that use electromagnetic power instead of chemical explosives to launch projectiles at high speeds.

If the moonjet concept ever becomes a reality, the authors found that it could be effective in reducing the amount of sunlight that reaches Earth. The aim would be to dim the sun by around 2 percent. Researchers estimate that this is the threshold for the desired impact on our planet's climate.

The team's work mapped out the efficiency of different types of dust for use as a solar shield. The researchers assessed how well a dust shield would work, depending on where it was deployed.

The moonjet was the most-effective approach for three reasons. First, there is a ready supply of lunar dust on the moon's surface. Second, the solar energy available there could be harvested. And, lastly, a low escape velocity is needed, compared with launching a shield from Earth.

"We considered the cost in terms of energy for deploying a dust shield, settling on the moonjet concept, not because it was most efficient, but because it seems the most sustainable," Bromley said. "The energy required is much less than launching from Earth.

"We are exploring this approach in case humanity needs more time to reduce greenhouse gas emissions," he added. "It is important to consider all possibilities."

But while the scientists found that the concept is feasible in theory, there would still be significant challenges to overcome to bring it to life.

"Millions of tons of dust per year would have to be collected and launched, but for context, individual open-pit mines on Earth have comparable or greater output," Bromley said. "Still, setting up an operation like this would be a huge undertaking."

Alan Robock is a professor in the Department of Environmental Sciences at Rutgers University, New Jersey. He has published research on geoengineering approaches to combating climate change but was not involved in the PLOS study. He said there are several drawbacks to mitigation strategies such as the dust-cloud solar shield.

"If people think it is a solution to global warming, they will not work as hard at mitigating emissions," Robock told Newsweek. "It would probably take decades to do and be very expensive.

"Global climate change from human injections of greenhouse gases is a real problem, but there is a much simpler, safer, and cheaper solution: leave the fossil fuels in the ground and run the world on solar and wind power. The problem is a political one, not a technical one."

The study authors wrote: "Much of the concept remains untested, from the lunar mining operation to the electromagnetic launcher. Still, we are heading in the right direction as NASA's Artemis mission gears up to explore the moon."

They found that, once launch facilities are established on the moon, large amounts of dust could be shot into space, quickly and continuously. This is a factor that they said could be "essential" if we do not correct our course on climate change.

One important feature of this concept is that the small grains of dust in the solar shield will experience the radiation pressure of sunlight. So, these grains would be swept away fairly quickly. The pressure would send them well clear of Earth and disperse them throughout the solar system.

While this means there would be no impact on Earth's atmosphere, the dust would have to be constantly replenished, the scientists found. It also means that the shield could be cleared away when no longer needed, Bromley said.

Whether or not such an idea would work in practice remains to be seen, and there is always the possibility of unintended consequences. The authors themselves also note in the paper that the lack of control of such a dust cloud "may limit its effectiveness as a solar shield."