Scientists propose using lunar dust to block sunlight. What are the risks?

The new strategy, a form of solar geoengineering, would require a regular stream of lunar dust being transported from the moon to Lagrange Point 1, which is the closest point the gravitational pull of the Earth and sun precisely equals the centripetal force required for a small object to move with them. As a point of reference, NASA's James Webb Space Telescope is orbiting in Lagrange Point 2, roughly one million miles from Earth.

The idea originated from the fact that the team typically studies planetary formation in distant galaxies. When planets are forming, they are typically shrouded in massive veils of dust that can block sunlight from reaching their surface. This dust also forms massive rings around the planets.

Using computer simulations, the researchers found that they could precisely launch a dust cloud from the moon to L1, and it would remain there for some time, creating a shade for Earth that would lower the temperature on our planet. They did note, however, that this veil could be easily blown off course by solar radiation, meaning a constant supply would likely be required.

Solar geoengineering is a controversial topic, as its effects could potentially be incredibly harmful to our planet. However, the researchers behind the new proposal explain that their method would have no effect on our atmosphere. It could also be reversed relatively quickly, as the only requirement would be halting the flow of lunar dust to L1.

Arguably, the IPCC's latest report also shows that we may have to take some risks when it comes to fighting the worst effects of climate change, with humanity's use of fossil fuels having broken temperature records that had stood for an estimated 125,000 years.

In an interview with IE, Dr. Scott J. Kenyon (Ph.D.), a theoretical astrophysicist from the Harvard–Smithsonian Center for Astrophysics and one of the scientists behind the study, explained the thinking behind the new method, as well as the potential negative implications.

The following conversation has been lightly edited for clarity and flow.

Interesting Engineering: What are the potential risks of solar geoengineering strategies? 

Dr. Scott J. Kenyon: I am not enough of an expert to comment on other strategies. For this one, where we studied the properties of dust particles and the strategies for placing them at L1, I see no real technological risk. The downside of launching dust from the moon to L1 is that if you miss the target; the dust then joins the rest of the small dust particles orbiting in the inner solar system.

The mass of the dust needed is 10 billion kg per launch, which is a lot compared to the 100,000 kg of dust that impacts the Earth every day. But it is small compared to the 30 million billion kg (I guess that is 30 quadrillion kg!) in the interplanetary dust cloud that lies in the inner Solar System. So, if the launch were to miss the L1 point, it would have little impact as the dust is dispersed around the inner solar system.

The societal risk seems rather daunting to me. I am not enough of an expert to estimate the costs of developing a base on the moon, the mining capability to collect the dust, and the launch capability to send it off to L1. But, the estimates I have seen in print just for a continuously occupied moonbase are enormous, especially compared to the costs of reducing greenhouse gas emissions from conservation and solar/wind/ocean power sources. It seems better to solve issues with rising temperatures in these simpler ways that we can implement now and spend the money needed for a launch facility (say) on other problems here on Earth.

IE: Do you think we are in a scenario, with the climate crisis, where we must face these risks?

I think that if we all worked together to reduce greenhouse gas emissions and turn to renewable energy sources, we would not need geoengineering solutions.

IE: What role did your work investigating planetary formation play in your new study?

During the formation of stars like the Sun, everyone comes with a disk capable of producing a planetary system like our own. When planets form, they leave behind rings of dust (similar to the asteroid and Kuiper belts) that absorb optical light from the central star and re-radiate it in the infrared.

[We] study how the planets and dust rings form and develop predictions for observational studies. We understand that these dust rings prevent some of the light from the central star from reaching beyond the ring. From there, it was clear that dust at L1 would reduce sunlight on Earth. The issue was how to get the dust there and whether it would last long enough to be interesting or useful. That was the focus of our research for this paper.

IE: Is there any argument to be made for launching dust from Earth, or is the lunar dust plan a clear winner?

Because the moon's gravity is one-sixth [that] of the Earth's and because the moon has no air resistance, it is clearly easier to launch anything from the moon. And it might be easier to collect dust from the surface than mining something like coal dust on Earth, especially when coal has good uses in manufacturing steel and other products.

IE: What benefit does your method hold over other solar geoengineering methods, such as stratospheric aerosol injection?

From what I have read (remember I am not an expert!), aerosol injection is technologically much easier, but it is more subject to wind direction and other variables of the atmosphere and may have some health issues. Our proposal has none of these, but of course it is way more expensive.

IE: Do you see the lunar dust method as a long-term solution? Or is it something that would be used as a stop-gap while we transition away from fossil fuels and find ways to remove CO2 from the atmosphere?

I hope that we solve the problem before we have the capabilities on the moon to implement our strategy. But, if we are unable to reverse warming before we have the capability, then I imagine it would be helpful to use this strategy as a stop-gap, where people would see that the expense required for launching moon dust is much less palatable than eliminating excess greenhouse gases.

IE: What are the next steps for yourself and your team?

For now, we are returning to planet formation!