Bold Plan to Dim the Sun by Blasting Moon Dust Into Space Could Help Cool Earth

The longest-reigning monarch in France's history, Louis XIV, earned the sobriquet le Roi Soleil or "the Sun King" because of, surprisingly, his love for ballet. It had nothing to do with the star at the center of our solar system. But weirdly enough, during Louis XIV's reign, the sun began acting a little strangely.

Sometime around 1645 its behavior changed. Sunspots became exceedingly rare. In some years, no sunspots were detected at all. The sun's energy dipped. This period, known as the Maunder Minimum, occurred within a "Little Ice Age" and coincided with a particularly cold spell in the North Atlantic around 1650.

Today, things are going in the opposite direction. The Earth is getting warmer even as the sun's energy has remained fairly stable. The chief reason for this increase in temperature is the burning of fossil fuels, which releases carbon dioxide into the atmosphere, trapping heat. Without a rapid curbing of CO2 emissions, temperatures are forecast to rise more than 1.5 degrees Celsius above preindustrial levels in the next few decades. The worst-case scenarios see temperature increases exceeding 2 and even 3 degrees. 

In the past few years, a controversial technofix has been floated as a solution: Why not dim the sun? This process, known as solar geoengineering, could involve a number of different mechanisms, but one of the more hotly debated ideas suggests spraying sulfur particles into the atmosphere, in a process that mimics the eruption of volcanoes. The reflective particles would then bounce the sun's rays back into space. 

Scientists and experts aren't yet convinced it's necessarily a good idea to even try this — it doesn't address the underlying cause of climate change and the potential consequences are not fully understood. There's a non-zero possibility that tampering with the atmosphere could bring about irreversible changes we've not considered and are not at all prepared for. It also might make us believe there's a way to reverse climate change without reducing carbon emissions. Spoiler: Nope.

But, what if, instead of depositing particles into the atmosphere, we dropped them off in space? What if we attempted some astroengineering?

In a new paper, published in the journal PLOS Climate on Wednesday, a trio of scientists discuss scenarios to do just that, shielding the sun's rays from the Earth by depositing reflective particles — dust — in space. Using computer simulations, the team discovered that one possibility is to use moon dust, blast it from the lunar surface into space and provide a temporary dimming of our home star.

Benjamin Bromley, a theoretical astrophysicist at the University of Utah and first author on the paper, notes that the trio did not set out to develop a climate solution and that they're not climate scientists. His normal line of research involves studying how planets form — and in that process, himself, computer science student Sameer Khan and Scott Kenyon, of the Smithsonian astrophysical observatory, found inspiration.

"Making planets involves collisions, and we learned from that research that a comparatively small amount of dust can go a long way in intercepting starlight," Bromley said. "That got us to think about dust as a way to dim the sun."

Bromley notes the proposal would mimic the scenario that occurred during the Little Ice Age, when Louis XIV reigned over France. You'd need a lot of dust but, provided you could get it into space, it would essentially work to reduce solar radiation, blocking around 1% to 2% of the light.

One of the team's first ideas was to deposit a platform that spits space dust out at the Lagrange point L1, which lies about 900,000 miles inside Earth's orbit, directly between the sun and the Earth. At this point, objects are kind of stuck in place by the gravity of the two bodies. (Indeed, the opposite Lagrange point, L2, is where the James Webb Space Telescope lies, outside Earth's orbit.)

The problem, in the simulations, was that the dust would quickly blow away from the L1 point. It wasn't stable enough to keep a dust shield in place.

So they looked a little closer to home: the moon. They produced simulations that demonstrated launching lunar grains from the moon toward L1 was the most promising strategy.

"Lunar dust stood out for two reasons," said Bromley "First, it can be pretty efficient at deflecting sunlight, and second, it turns out that the most efficient grain size is the most plentiful on the moon's surface."

This, he notes, was a fun surprise and something they didn't know going into the project. One of the problems, though, is just how much dust is required. It would be cost prohibitive to constantly send rockets full of space dust to a platform out at L1, so the moon provides a second advantage. 

"If we can get the infrastructure to the lunar surface, launching the dust from there is much easier because of the moon's weaker gravity compared with Earth," Bromley said.

But what happens once the dust is out there in space? Fortunately, the simulations showed that the dust grains didn't end up raining back down on Earth. Instead, they would drift outward from the sun, on a journey into the infinite dark.

The trio's suggestion isn't the only space-based solar shield that's been proposed. A similar proposal to use lunar dust was made in 2007 by Curtis Struck at Iowa State University. Last year, a team of scientists at MIT proposed the idea of "space bubbles." The idea is exactly what it sounds like: create a raft of bubbles in space, at L1, to deflect incoming sunlight. This process would be reversible. 

All these methods come with a caveat: They're not going to be implemented quickly enough to halt the current temperature increase. But if we put the planet on an irreversible path to a hothouse, we might need to turn to a "break glass in case of emergency" solution. You can add moon dust to that list. 

"If we get to a point where dimming the sun is a needed step, lunar dust should be explored as an option, despite the technological challenges," says Bromley.