A cosmic origin of Venus’ lower haze

Abstract

Entry probes have revealed a layer containing involatile submicrometre particles—the lower haze—between Venus’ surface and the main cloud deck. However, its origin is still unclear, and atmospheric models have mostly treated it as a lower boundary condition, despite the known role of its particles as condensation nuclei when they are transported to the main cloud deck. Here we incorporate a self-consistent particle formation framework into a Venus cloud microphysics model and show that the continuous influx of cosmic dust is sufficient to sustain this lower haze layer with the particle size distribution observed by the entry probes. These haze particles of cosmic origin act as efficient condensation nuclei, promoting cloud formation in the main cloud deck even far from their initial source. Furthermore, these particles are enriched in metallic species, specifically magnesium and iron; the latter represents a plausible source for the planet’s long-unidentified ultraviolet absorber. Collectively, our findings establish cosmic dust as an essential component of Venus’ climate. These insights are also crucial for understanding the climates of planets with thick atmospheres, such as gas giants and exoplanets, where accumulating cosmic dust can similarly affect the cloud structure and composition.