Tuesday, July 23, 2024

A bold solution to combat climate change?


A dusty lunar landscape, as visualized by NASA’s Advanced Concepts Laboratory. Credit: NASA

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

A study led by the University of Utah explored the possibility of using dust to ward off sunlight. They analyzed the different properties of the dust particles, the amounts of dust, and the orbits best suited to shadow Earth. The authors found that shooting dust from Earth to a station en route at the Earth-Sun “Lagrangian point” (L1) would be more efficient but would require an astronomical cost and effort. An alternative is to use moondust. The authors argue that the release of lunar dust from the Moon could be a cheap and effective way to shadow Earth.

Dust is like a sun shield

Simulated release of a stream of dust between Earth and the Sun. This dust cloud appears as it crosses the sun’s disk, from Earth. Streams like these, including those released from the lunar surface, could act as a temporary umbrella for the sun. Credit: Ben Bromley/University of Utah

The team of astronomers applied a technique used to study the formation of planets around distant stars, which is their usual research focus. Planet formation is a chaotic process that releases a lot of cosmic dust that can form rings around the host star. These rings intercept the light from the central star and re-radiate it in a way that we can detect on Earth. One way to discover stars forming new planets 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.

Halostream Jet

Simulation of dust released from the waystation at Lagrange point 1. The shadow on the ground is exaggerated for clarity. Credit: Ben Bromley

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

The paper was recently published in the journal PLOS climate.

cast shade

The shield’s overall effectiveness depends on its ability to maintain an orbit that shadows the Earth. Sameer Khan, an undergraduate student and co-author of the study, led the initial exploration that orbitals could trap dust in position long enough to provide adequate shading. Khan’s work demonstrated 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 simply use the laws of gravity to track the simulated position of the sun shield over time for several different orbits,” Khan said.

There were two promising scenarios. In the first scenario, the authors place a space platform at the L1 Lagrange point, which is the closest point between Earth and the Sun where gravitational forces balance out. Objects in Lagrangian points tend to stay along a path between two celestial bodies, which is why[{” attribute=””>James Webb Space Telescope (JWST) is located at L2, a Lagrange point on the opposite side of the Earth.

Moon Dust Jet

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

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