The yellowish lower haze in Venus's atmosphere, first observed by the Venera and Pioneer Venus probes in the 1970s, has finally been explained. A research team led by planetary scientist Hiroki Karyu at Tohoku University used a microphysical model to show that the haze is made of cosmic dust left behind by meteorites burning up in the atmosphere. The study appears in Nature Astronomy.
Earlier speculation pointed to volcanic ash, since Venus is highly volcanic, or surface dust. Karyu's model ruled out both: even much larger influxes of those particles would not interact with the atmosphere's sulfur in the way needed to form the haze. Instead, the process works like cloud formation on Earth. Meteorite particles act as condensation nuclei, and sulfuric acid droplets condense around them. The droplets grow heavy, sink into the lower atmosphere, and evaporate at temperatures around 100°C, leaving the haze particles behind.
The finding also solves a second mystery. Something in Venus's atmosphere absorbs ultraviolet rays, and iron sulfate—detected by the Venera, Vega, and Pioneer Venus probes—now matches the haze's properties. The researchers suggest the same mechanism may apply to gas giants like Jupiter, Saturn, and Neptune, where meteorite particles could influence cloud and haze formation.