A company that aims to make billions of dollars by cooling the Earth has lifted the veil of secrecy that until now has hidden its plans for preventing sunlight from overheating the planet.
It hinges on aerosol particles that are 125 times smaller than the tiniest grain of sand.
Stardust Solutions has raised $75 million since 2023 from investors who are betting that global warming could get so out of control that governments might decide to pay the Israeli-U.S. startup to spray millions of tons of sunlight-reflecting aerosols into the stratosphere. Its plans were so guarded that it required scientists to sign nondisclosure agreements before they could study its potentially planet-altering technologies.
On Thursday, the company revealed the makeup of its proprietary particles. They are made of what’s known as amorphous silica and are 0.5 microns in size — only visible with a microscope. The startup also shared information about the systems it could use to disperse the spherical silica particles some 11 miles above the ground and monitor them as they fall back to the Earth.
“Our premise from the start was that the only way sunlight reflection technology would be considered by governments is if we provided robust scientifically-based solutions to all the challenges and concerns and proved it to be safe, practical, and controllable,” Stardust CEO Yanai Yedvab said in a statement. “That is the mission we took upon ourselves, and the details we are releasing today represent a major step toward that goal.”
The company is a leader in solar geoengineering — the hypothetical pursuit of altering clouds or changing other characteristics of the atmosphere in ways that would interrupt sun rays before they hit the Earth. Other ideas envision building massive sun shades in space or creating bubbly mixtures of reflective sea foam to limit the amount of heat absorbed by the oceans.
Geoengineering is unlike other responses to climate change because, while it can theoretically reduce warming, it does not address the root cause: the burning of fossil fuels. That means the world would be effectively hooked on solar geoengineering until nations reduce their use of oil, gas and coal to safe levels and then remove excess climate pollution from the air and seas.
Stardust’s revelations came as President Donald Trump and Chinese President Xi Jinping held a rare bilateral summit in Beijing and after record-breaking heat and drought this year have triggered historic wildfires in the U.S. and Southeast Asia. While climate change and geoengineering was not on summit agenda, both countries’ support — or tacit acceptance — would likely be necessary for Stardust to deploy its particles and repay its investors, according to analysts.
“Just given their size, they’re key players in all this,” said Erin Sikorsky, who served on the National Intelligence Council during the Obama administration, referring to the U.S. and China. She now leads the Center for Climate and Security, a think tank. “They could stop somebody from doing this if they wanted to. And so that matters to a company like Stardust.”
Yedvab, the company’s CEO, said in an email that the timing of the release was “not connected” to the U.S.-China summit.
The new details about Stardust’s silica particles and other systems were disclosed in six academic papers that it posted online. Most of the papers were written with experts at leading universities, but they have not yet undergone peer review — a critical step in the scientific publishing process where other experts review and comment on the findings.
The company is currently seeking patents for its particles and other technologies — a key component of its business strategy. Stardust said it is also submitting the papers to scientific journals.
Stardust is developing two types of amorphous silica-based particles. One is “fully bio-safe, manufacturable at scale today, and at a very advanced stage of validation,” according to a summary of the research. Another similarly sized version of the silica particle includes a calcium carbonate core that it said would more effectively block solar radiation.
“Both designs are intentionally engineered to recycle into existing natural cycles after they settle to the ground,” the summary said.
Amorphous silica has a different atomic structure than crystalline silica, the reactive, hazardous dust released by cutting or crushing certain types of rocks. Stardust is not using crystalline silica in its process. Amorphous silica isn’t known to pose a risk to humans at low doses, according to the World Health Organization’s cancer research agency.
Stardust has previously pitched investors on a plan for “global full-scale deployment” as soon as 2035, according to an investor deck previously reported by POLITICO Magazine. At that point, the company’s expected revenues would be around $1.5 billion annually, the deck said. Stardust has said the presentation from 2023 no longer reflects its current thinking.
Some scientists remain wary of Stardust and other solar geoengineering companies. They fear that the technology could be misused at a time when international cooperation is fraying.
“This announcement is a clear example of why self governance led by for-profit entities does not work,” said Shuchi Talati, the executive director of the Alliance for Just Deliberation on Solar Geoengineering, a nonprofit that seeks to include marginalized countries and communities in debates over sunlight-reflecting technologies.
Stardust, she said, “cannot create their own principles and then applaud themselves for following them. They cannot define safety according to their own standards and then self-certify that they meet them. The field requires coordinated, legitimate, and independent research governance.”
Talati’s alliance is working with the Natural Resources Defense Council, the American Geophysical Union and other groups to set standards for solar geoengineering research and development.
“It rarely works out well when those who develop globally significant technology are also in charge of governing it,” added Hannah Safford, a White House climate policy adviser during the Biden administration.
“In the United States, government has shown more interest in banning climate science than in thoughtfully governing emerging technology,” said Safford, who is now at the Federation of American Scientists, a think tank. “That leaves the door wide open for other countries, companies, and individuals to run out in front — and we might not like the choices they make.”
