Meteorites often contain metals such as magnesium, silicon and iron, and iron compounds were previously suspected to act as absorbers. The magnesium and silicon contained in meteorites absorb terrible UV radiation. But iron was more promising; Venera and the Vega probes had detected atmospheric iron, while the mass spectrometer aboard the Pioneer Venus Large Probe found the compound iron sulfate, but these discoveries remained unexplained for decades.
The lingering suspicion that iron compounds were the mysterious absorber was confirmed when researchers discovered that iron sulfate matched the properties of the haze.
It turns out that for haze particles at a certain altitude (40 to 50 km or about 25 to 31 miles above the surface), condensation is not possible because the high energy of the particles creates a barrier that prevents sulfuric acid droplets from sticking to their surface. (This is called a nucleation barrier.) Particles with a strong nucleation barrier are transported by the hotter air rising as a result of convection into the upper cloud layer, where they cool enough to be incorporated into sulfuric acid particles. While previous observations suggested this, Karyu’s team now has stronger evidence.
This discovery has implications for other planets. The upper haze of gas giants has been studied ad nauseam, but the microphysical processes beneath the main cloud layer remain a mystery. Venus may have unlocked at least some of the haze’s secrets. On a planet like Jupiter, particles that cannot evaporate, such as those from meteorites, could be deposited on the outer cloud layers. Further studies could provide further insights into how cosmic dust promotes cloud and haze formation on planets such as Jupiter, Saturn and Neptune.
“As on Venus, observing the metal layers in the atmosphere of the outer planets would be helpful [determine] the deposition rates of [metals] in their atmospheres and thus in the resulting haze abundance,” Karyu said. “These effects make cosmic dust an essential component of the planet’s climate, a role that is likely important for exoplanets as well.”
Nature Astronomy, 2026. DOI: 10.1038/s41550-026-02843-4
