Can a daring approach address the challenge of climate change?

On a cold winter day, the sun’s warmth is most welcome. However, as humanity releases more and more greenhouse gases, Earth’s atmosphere traps more and more of the sun’s energy and continues to warm the Earth. One strategy to reverse this trend is to intercept some of the sun’s rays before they reach our planet. For decades, scientists have considered using screens, objects or dust particles to block enough of the sun’s radiation—between 1 and 2%—to reduce the effects of global warming.

A study led by the University of Utah explored the possibility of using dust to block sunlight. They analyzed the various properties of dust particles, the amount of dust, and the most suitable orbit for shadowing Earth. The authors found that shooting dust from Earth at a station en route at the Earth-Sun (L1) “Lagrangian point” would be more efficient but would require enormous cost and effort. The alternative is to use moondust. The authors argue that the ejection of lunar dust from the Moon could be a cheap and effective way to shadow Earth.

The team of astronomers applied a technique used to study planet formation around distant stars, which is usually the focus of their research. Planet formation is a chaotic process that releases large amounts of cosmic dust which can form rings around their host stars. These rings intercept light from the central star and re-radiate it in ways we can detect on Earth. One way to find new planet-forming stars is to look for these dusty rings.

“That was the seed of the idea,” said Ben Bromley, professor of physics and astronomy and lead author of the study.

Simulation of dust being released from the waystation at Lagrange 1 point. The shadow on the ground is made clearer. Credit: Ben Bromley

said Scott Kenyon, study co-author from the Center for Astrophysics | Harvard and Smithsonian.

This paper was recently published in the journal PLOS climate.

cast shade

The shield’s overall effectiveness depends on its ability to maintain Earth’s shadowing orbit. Sameer Khan, an undergraduate student and co-author of the study, led early exploration that the orbital could trap dust in position long enough to provide adequate shading. Khan’s work demonstrates the difficulty of keeping dust where you want it.

“Because we know the locations and masses of the major celestial bodies in our solar system, we can easily use the law of gravity to track the simulated position of the sun visor over time for several different orbits,” said Khan.

There are two promising scenarios. In the first scenario, the authors place the space platform at the L1 Lagrange point, which is the closest point between the Earth and the Sun where the gravitational forces are balanced. Objects at a Lagrangian point tend to stay in a path between two celestial bodies, which is why[{”attribute=””>JamesWebbSpaceTelescope(JWST)islocatedatL2aLagrangepointontheoppositesideoftheEarth[{”attribute=””>JamesWebbSpaceTelescope(JWST)islocatedatL2aLagrangepointontheoppositesideoftheEarth

A simulation of dust launched from the moon’s surface as seen from Earth. Credit: Ben Bromley

In computer simulations, the researchers shot test particles along the L1 orbit, including the position of Earth, the sun, the moon, and other solar system planets, and tracked where the particles scattered. The authors found that when launched precisely, the dust would follow a path between Earth and the sun, effectively creating shade, at least for a while. Unlike the 13,000-pound JWST, the dust was easily blown off course by the solar winds, radiation, and gravity within the solar system. Any L1 platform would need to create an endless supply of new dust batches to blast into orbit every few days after the initial spray dissipates.

“It was rather difficult to get the shield to stay at L1 long enough to cast a meaningful shadow. This shouldn’t come as a surprise, though, since L1 is an unstable equilibrium point. Even the slightest deviation in the sunshield’s orbit can cause it to rapidly drift out of place, so our simulations had to be extremely precise,” Khan said.

In the second scenario, the authors shot lunar dust from the surface of the moon towards the sun. They found that the inherent properties of lunar dust were just right to effectively work as a sun shield. The simulations tested how lunar dust scattered along various courses until they found excellent trajectories aimed toward L1 that served as an effective sun shield. These results are welcome news, because much less energy is needed to launch dust from the moon than from Earth. This is important because the amount of dust in a solar shield is large, comparable to the output of a big mining operation here on Earth. Furthermore, the discovery of the new sun-shielding trajectories means delivering the lunar dust to a separate platform at L1 may not be necessary.

Just a moonshot?

The authors stress that this study only explores the potential impact of this strategy, rather than evaluate whether these scenarios are logistically feasible.

“We aren’t experts in climate change, or the rocket science needed to move mass from one place to the other. We’re just exploring different kinds of dust on a variety of orbits to see how effective this approach might be. We do not want to miss a game changer for such a critical problem,” said Bromley.

One of the biggest logistical challenges—replenishing dust streams every few days—also has an advantage. Eventually, the sun’s radiation disperses the dust particles throughout the solar system; the sun shield is temporary and shield particles do not fall onto Earth. The authors assure that their approach would not create a permanently cold, uninhabitable planet, as in the science fiction story, “Snowpiercer.”

“Our strategy could be an option in addressing climate change,” said Bromley, “if what we need is more time.”

Reference: “Dust as a solar shield” by Benjamin C. Bromley, Sameer H. Khan and Scott J. Kenyon, 8 February 2023, PLOS Climate.
DOI: 10.1371/journal.pclm.0000133