Could microscopic spheres of silica help cool the planet?
May 21st 2026|CHICAGO|5 min read
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IN FEBRUARY 2024 an article in the Wall Street Journal revealed that Stardust Solutions, an Israeli startup, was developing tiny particles which, if lofted into the stratosphere in sufficient number, might be used to cool the Earth. The idea of putting stuff into the stratosphere to lower temperatures was not new; it is the most discussed of the various sunlight-blocking technologies gathered under the rubric of solar geoengineering. Stardust’s novelty was that it claimed to be developing special particles which might do particularly well. What it was that made them so super, though, remained a secret.
That secrecy ended last week. On May 14th the company published preprints of papers which it is submitting to peer-reviewed journals describing its particles in detail. Most of the company’s data, it turns out, concerns spheres less than a thousandth of a millimetre across and made entirely of amorphous silica (the same stuff that opals are made of) with a specially treated surface. A second, similarly sized version has a surface shell of amorphous silica but a core of calcium carbonate.
In an interview at a meeting on geoengineering hosted by the Climate Systems Engineering initiative (CSEi) at the University of Chicago a few days after the preprints were uploaded, Yanai Yedvab, Stardust’s boss, stressed the degree to which the particles were part of an “end to end” approach to geoengineering technology which the company hoped to provide to any governments which might, eventually, decide that geoengineering is a good idea. The reception was decidedly mixed.
Although the use of calcium carbonate and silica to these ends has been explored before, it has never been done in such depth. The lion’s share of research on stratospheric geoengineering assumes instead that the cooling would be done by mimicking the cooling effect of large volcanic eruptions: in other words, injecting a sulphur-rich chemical high into the atmosphere, where the sulphur ends up in tiny reflective droplets.
There is a problem with this approach which has nothing to do with climate. Breathing in sulphate particles is bad for people. And particles high up in the stratosphere will inevitably drift down. The amount of sulphate that would be used would, admittedly, be small relative to the total quantities emitted by industry, and it would not be concentrated close to where people live. Nevertheless, when Dr Yedvab says “Dispersing millions of tonnes of toxic materials above the heads of their children for decades is something [people] wouldn’t feel that comfortable about,” it is hard to disagree.
Amorphous silica is not in itself a health concern. But that does not mean that the Stardust particles will necessarily be safer than sulphates after a few years of weathering. On this and other matters—such as the idea that the particles could be chemically tagged—the scientists gathered in Chicago seemed unconvinced. “I think the work they’ve done on the particles is really terrific,” says David Keith, CSEi’s faculty director and a longtime leader in geoengineering research. “What I don’t buy is that it’s definitely safer or definitely a good thing.”
It might be tempting to see this as a reflexive resistance to incomers. But there is something deeper at play. Almost all geoengineering researchers, as well as the charities which fund a significant part of their work, say they do so disinterestedly, equally happy to discover good news or bad. (The Degrees Initiative, a British charity which funds such research and takes that stance, is chaired by a member of The Economist’s editorial staff.) Stardust, by contrast, is a commercial undertaking. If its technology is never used, its investors will lose out. That means it has a vested interest in geoengineering going ahead, and in perpetuating a dim view of sulphates.
“It’s not that there’s anything fundamentally wrong with for-profit companies,” said Dakota Gruener, who runs Reflective, a philanthropically funded solar-geoengineering research outfit, in an onstage discussion with Dr Yedvab at the Chicago meeting. “But when you have investors who are saying what we bet upon is that this will be deployed, it makes it hard to have that same level of objectivity.”
Objectivity tends to engender a sense of trust. So does transparency—a norm in the field that was challenged by Stardust’s long silence. It does not help the case for trust that its original funding came through Awz Ventures, a technology investor based in America, Canada and Israel that has various links to intelligence and security services. Awz also has an advisory board led by Stephen Harper, a former prime minister of Canada noted for his friendliness to the fossil-fuel industry.
Perhaps more important than the source of its funds, though, is their quantity. In October 2025 the original investment of $15m through Awz was joined by a second round of investors bringing in $60m. (One of those investors was the venture-capital arm of Exor, a shareholder in The Economist’s parent company.) A survey of research funding published by SRM360, a non-profit which provides information about solar geoengineering, suggests that this makes Stardust easily the most generously funded research outfit in the field.
Solar geoengineering has long been controversial. Those studying it have nonetheless made real progress in understanding its potential, and its scope for misapplication. Stardust’s ideas may in the long run be seen as a fruitful contribution to that progress. In the short run, it may well add to the controversy. ■
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This article appeared in the Science & technology section of the print edition under the headline “A load of (very tiny) balls”
From the May 23rd 2026 edition
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