Space dust, including that launched from the Moon, can protect the Earth from climate change by acting as a sunshield, a new study suggests. Greenhouse gases emitted due to various human activities form a blanket around Earth, and trap the Sun's energy. This increases Earth's temperature gradually, and is one of the reasons behind global warming. In order to avoid the trapping of heat by greenhouse gases, a fraction of the sunlight must be intercepted before it reaches Earth, according to the study.
Scientists, for decades, have tried to mitigate the effects of global warming by using screens or other objects to block about one to two per cent of the Sun's radiation. A team of scientists at the Center for Astrophysics | Harvard & Smithsonian, and the University of Utah, who led the new study, have explored the potential of using dust to shield sunlight.
The study describing the findings was published February 8, 2023, in the journal PLOS Climate. The authors have described different properties of dust particles, quantities of dust, and the orbits that would be best suited for shading Earth.
Why dust should be launched to the Lagrange Point between Earth and Sun
They found that launching dust from Earth to a way station (a stopping point during a journey) at the "Lagrange Point" between Earth and Sun would be the most effective way of shading Earth. A Lagrange Point is a position in space where the gravitational forces of a two-body system like the Sun and Earth produce enhanced regions of attraction and repulsion, and can be used by spacecraft or other objects as a "parking point" in space to remain in a fixed position.
However, launching dust to a Lagrange Point between the Earth and Sun would require an astronomical cost and effort.
Why is moondust a better alternative than other space dust?
Therefore, the researchers have proposed moondust as an alternative, because dust from the Moon can be launched in a low-cost and effective way. Moondust will also be able to protect Earth from climate change.
In a statement released by the Center for Astrophysics, Scott Kenyon, a co-author on the paper, said it is amazing to contemplate how moondust, which took over four billion years to generate, might help slow the rise in the Earth's temperature, a problem that took humans less than 300 years to produce.
What technique did the astronomers use?
The researchers applied a technique to study planet formation around distant stars to the lunar dust concept. Planet formation begins with astronomical dust forming rings around host stars. These rings intercept light from the central star, and then re-radiate it. The re-radiated light can be detected by astronomers to understand planet formation.
Ben Bromley, professor of physics and astronomy at the University of Utah, and lead author on the paper, said the seed of the idea was that if they took a small amount of material and put it on a special orbit between Earth and the Sun, and they broke it up, they could block out a lot of sunlight with a little amount of mass.
What determines the effectiveness of a sunshield?
According to the researchers, the overall effectiveness of a sunshield would depend on its ability to sustain an orbit that casts a shadow on Earth. This means, the sunshield should have such an orbit that it intercepts light from the Sun at all points of time, and hence, shade Earth. Sameer Khan, a co-author on the paper, led the initial exploration into which orbits could hold dust in position long enough to provide adequate shading to Earth.
Khan said that since the positions and masses of the major celestial bodies in the solar system are known, the laws of gravity can be used to track the position of a simulated sunshield over time for several different orbits.
First scenario: Positioning a platform at L1 Lagrange Point
The researchers found two scenarios to be promising. The authors, in the first scenario, positioned a space station platform at the L1 Lagrange Point, the closest point between Earth and the Sun where the gravitational forces are balanced. The reason why the James Webb Space Telescope (JWST) is located at L2, a Lagrange point on the opposite side of Earth, is that objects at Lagrange points tend to stay along a path between two celestial bodies.
Limitations of first scenario
The researchers used computer simulations to shoot particles from the platform to the L1 orbit. They also simulated the position of Earth, the Sun, the Moon and other planets of the solar system, and tracked where the particles scattered.
When launched precisely, the dust followed a path between Earth and the Sun, and effectively created shade, at least for a while.
However, solar winds, radiation, and gravity within the solar system easily blew the dust off course.
Any L1 space station platform will need to create an endless supply of new dust batches into orbit every few days after the initial spray dissipates, the team concluded.
Khan said it was rather difficult to get the shield to stay at L1 long enough to cast a meaningful shadow, but that should not come as a surprise, because L1 is an unstable equilibrium point. He added that even the slightest deviation in the sunshield's orbit can cause it to rapidly drift out of place, so their simulations had to be extremely precise.
Second scenario: Launching lunar dust from Moon
The authors, in the second scenario, shot lunar dust from a platform on the surface of the Moon towards the Sun, and found that the inherent properties of lunar dust were just right to effectively work as a sunshield. Using the simulations, they tested how lunar dust scattered along various courses until they found excellent trajectories aimed toward L1 that served as an effective sunshield.
Advantages of the second scenario
The team said that much less energy is needed to launch dust from the Moon than Earth. Since the amount of dust required for a solar shield is large, comparable to the output of a big mining operation on Earth, it is important to ensure that less energy is used to launch the dust in order to use it as a sunshield.
Kenyon said it is astounding that the Sun, Earth, and Moon are in just the right configuration to enable this kind of climate mitigation strategy.
The authors noted in the paper that the study only explores the potential impact of the strategy, but does not evaluate whether these scenarios are logistically feasible.
Bromley said the researchers are not experts in climate change, or the rocket science needed to move mass from one place to another, but are just exploring different kinds of dust in a variety of orbits to see how effective this approach might be.
Replenishing dust streams every few days is one of the biggest logistical challenges. However, it also has an advantage, the authors said.
This is because the Sun's radiation naturally disperses the dust particles throughout the solar system, implying that the sunshield is temporary, and particles do not fall onto Earth. Therefore, this approach would not create a permanently old, uninhabitable planet as in the science fiction story, "Snowpiercer", the authors said.