On a cold winter day, the warmth of the sun is welcome. Yet, as humanity emits more and more greenhouse gases, the Earth’s atmosphere increasingly traps the sun’s energy and steadily increases the Earth’s temperature. One strategy to reverse this trend is to intercept a fraction of sunlight before it reaches our planet. For decades, scientists have considered using screens, objects or dust particles to block just enough solar radiation – between 1 and 2% – to mitigate the effects of global warming.
A study led by the University of Utah explored the potential of using dust to shield sunlight. They analyzed different properties of dust particles, the amounts of dust and the orbits that would be best suited to shadow the Earth. The authors found that launching dust from Earth to a pass-through station at the “Lagrange point” between Earth and the sun (L1) would be the most efficient but would require astronomical cost and effort. An alternative is to use moon dust. The authors argue that launching lunar dust from the moon might be a cheap and effective way to shadow Earth.
The team of astronomers applied a technique used to study planet formation around distant stars, their usual research focus. Planet formation is a messy process that kicks up a lot of astronomical dust that can form rings around the host star. These rings intercept the light from the central star and retransmit it so that we can detect it on Earth. One way to find stars that form new planets is to look for these dusty rings.
“That was the seed of the idea; if we took a small amount of matter and put it in a special orbit between the Earth and the Sun and broke it, we might block a lot of sunlight with a small amount of mass,” said Ben Bromley, professor of physics and astronomy and lead author of the study.
“It’s amazing to imagine how moon dust – which took more than four billion years to generate – might help slow Earth’s temperature rise, a problem that took us less than 300 years to happen,” said Scott Kenyon, co-author. of the study of the Center for Astrophysics | Harvard & Smithsonian.
The article was published on Wednesday, February 8, 2023 in the journal PLOS Climate.
cast a shadow
The overall effectiveness of a shield depends on its ability to maintain an orbit that casts a shadow on the Earth. Sameer Khan, an undergraduate student and co-author of the study, led the initial exploration in which orbits might hold dust in position long enough to provide adequate shading. Khan’s work demonstrated the difficulty of keeping dust where you need it.
“Because we know the positions and masses of the major celestial bodies in our solar system, we can simply use the laws of gravity to track the position of a simulated sunshade over time for several different orbits,” said Khan said.
Two scenarios were promising. In the first scenario, the authors positioned a space platform at the Lagrange point L1, the closest point between Earth and the sun where gravitational forces balance. Objects at Lagrange points tend to stay along a path between the two celestial bodies, which is why the James Webb Space Telescope (JWST) is located at L2, a Lagrange point on the opposite side of Earth .
In computer simulations, the researchers shot test particles along the L1 orbit, including the position of the Earth, sun, moon and other planets in the solar system, and tracked where the particles have dispersed. The authors found that when thrown with precision, the dust would follow a path between the Earth and the sun, creating shadow, at least for a while. Unlike the 13,000-pound JWST, the dust was easily blown around by solar winds, radiation, and gravity in the solar system. Any L1 platform should create an endless supply of new batches of dust to send into orbit every few days following the initial spray dissipates.
“It was rather difficult to get the shield to stay at L1 long enough to cast a meaningful shadow. This should come as no surprise, however, since L1 is an unstable equilibrium point. Even the slightest deviation in the sunvisor’s orbit can cause it to quickly drift out of place, so our simulations had to be extremely accurate,” Khan said.
In the second scenario, the authors threw lunar dust from the surface of the moon towards the sun. They discovered that the inherent properties of lunar dust were perfect for it to work effectively as a sunscreen. The simulations tested how lunar dust dispersed along different paths until they found excellent paths directed toward L1 that served as an effective sunshade. These results are good news, because it takes much less energy to launch dust from the Moon than from Earth. This is important because the amount of dust in a sunscreen is significant, comparable to the production of a large mining operation here on Earth. Additionally, the discovery of the new sunshade trajectories means that lunar dust delivery to a separate platform at L1 may not be necessary.
Just a moonshot?
The authors emphasize that this study only explores the potential impact of this strategy, rather than assessing whether these scenarios are logistically feasible.
“We are not experts in climate change or the rocket science needed to move mass from place to place. We’re just exploring different kinds of dust in a variety of orbits to see how effective this approach might be. We don’t want to miss a game changer for such a critical issue,” Bromley said.
One of the biggest logistical challenges — replenishing dust streams every few days — also has an upside. Eventually, solar radiation disperses dust particles throughout the solar system; the sun shield is temporary and shield particles do not fall to Earth. The authors assure that their approach would not create an uninhabitable and permanently cold planet, as in the science fiction story “Snowpiercer”.
“Our strategy might be an option to tackle climate change,” Bromley said, “if we need more time.”
