A Sunshade to Protect the Earth’s Climate Would be Perforated by Micrometeoroids
When a meteor exploded over the Pacific Ocean on January 8, 2014, its fireball released numerous molten droplets which landed on the ocean floor. We know that because the research team of the Galileo Project collected some of these spherules in an expedition to the meteor site on June 14–28, 2023. By now, our scientists analyzed the retrieved sample of 850 spherules in the laboratory of Professor Stein Jacobsen at Harvard University, and identified a new class of differentiated elemental composition, BeLaU, never reported before for solar system materials. Our findings were just reported in two new publications, here and here.
Imagine yourself on the open deck of a ship which happened to sail just under this meteor’s fireball in 2014. Given the rainy weather at that location, you might have had an umbrella next to you as I did during our expedition. In that case, your instinct would be to shield your body by opening the umbrella overhead and hope for protection against the rain of molten droplets from the meteor. The only problem is that the thin film making the umbrella would have been perforated instantly by the iron droplets, offering no protection whatsoever. This thought crossed my mind when I read yesterday a major story on the front page of the printed New York Times, regarding an initiative to protect the Earth’s climate from rising temperatures by a sunshade.
Currently, the Planetary Sunshade Foundation proposes to counter climate change on Earth by blocking sunlight with a giant sunshade. The idea of a sunshield dates back to 1989 when James Early published a paper suggesting a “space-based solar shield to offset greenhouse effect”, positioned at the Lagrange Point L1 between Earth and the Sun, 1.5 million kilometers away from Earth or about four times the Earth-Moon separation, where the gravitational pulls from the Earth and Sun cancel each other. In 2006, the astronomer Roger Angel proposed releasing trillions of very lightweight spacecraft and using a transparent film of micrometer thickness combined with a steering technology that would prevent the devices from drifting off orbit. The thinness of the proposed structure would minimize its total mass and make the engineering challenge of transporting materials manageable.
In order to keep the world’s average temperature from rising above 1.5 degrees Celsius (2.7 degrees Fahrenheit) over current averages, the physicist Dr. Yoram Rozen from the Technion in Israel, proposed recently a sunshade made of many solar sails with an area of about a million square miles.
Erecting any of these “megastructures” in space would be very expensive and require a major international collaboration through reallocation of funds from military budgets to peaceful purposes. Given the current political turmoil, including a risk for a global war in the Middle East, this plan may appear as dreamy as the words of John Lennon “Imagine all the people livin’ life in peace…And the world will live as one.”
But we must keep in mind that political impossibilities could become a reality at times of despair, especially when a catastrophe is looming over the entire Earth.
Nevertheless, in difference from politics, the laws of physics are not negotiable. As a physicist, my concern is that the sunshade will be punctured through impacts by micrometeoroids and dust. A sudden destruction of the shade by a solid impactor could trigger a global catastrophe in a world that was counting on being protected by a thin umbrella.
Based on terrestrial data, impactors of centimeter size hit the Earth every 15 seconds. Given that the total double-sided surface area of the shade is about a percent of the area of Earth, this suggests that centimeter-size objects will impact the shade every 25 minutes at speeds of tens of kilometers per second — ten times faster than rifle bullets, creating holes larger than their size through any reasonable layer of material. Over a year, there will be 20,000 holes created by these centimeter-size impactors, separated from each other by about 10 kilometers. After a millennium, the shade will be perforated and resemble a colander with centimeter-scale holes separated by 300 meters from each other.
Impacts by smaller particles are more common. Particles smaller than 0.05 millimeters are expected to impact each centimeter squared once per 30 years. Particles smaller than a few micrometers would impact a centimeter squared every week. If, as proposed by Roger Angel, the sunshield will be made of a micrometer-thick film, impact by dust particles and micrometeoroids would puncture the entire surface within a million years. If a thin megastructure is placed closer to Earth, space debris from broken satellites and rockets would damage it faster.
These expectations were confirmed by the unplanned “particle detector” with an area of about 40 squared meters and a price tag of 10 billion dollars that NASA placed at the Lagrange Point L2 in December 2021. During the first year after launch of this unprecedented “micrometeoroid detector”, also known as the James Webb Space Telescope, engineers detected more than 20 micrometeoroid impacts to the telescope, most of them inconsequential, but one with a size approaching 0.1 millimeters caused a dimple in the mirror. Following that, NASA adjusted the Webb telescope operations to reduce the frequency of micrometeoroid hits.
The threat from impactors must be considered in any infrastructure we build in space, including on the surfaces of the Moon and Mars. The non-avian dinosaurs would have been first to advise us to watch out for impactors if only any of them survived, but unfortunately they were all eliminated from the surface of Earth by a rock the size of Manhattan Island. The PanSTARRS observatory in Hawaii and the Vera C. Rubin Observatory in Chile were constructed to warn us from near-Earth objects larger than a football field. But it would be far more challenging to protect a thin film in space from the impact of dust grains. The future livelihood of the human species should not be hanging on the balance by the protection of a thin film.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He chairs the advisory board for the Breakthrough Starshot project, and is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. His new book, titled “Interstellar”, was published in August 2023.
