Bound Water in Venus Clouds Rewrites Cloud Chemistry
A 2025 reanalysis of data from NASA’s Pioneer Venus Large Probe’s 1978 descent suggests Venus’s cloud aerosols may be about 60% water by mass, largely bound in hydrated ferric sulphates (and possibly magnesium sulphates), with most water released only upon heating. This points to hydrated salts as part of cloud composition and does not overturn the sulfuric-acid model, but it does complicate the simple acid-water picture. The finding comes from a single historic descent and could reflect sampling artefacts, so confirming evidence from future dedicated missions (e.g., DAVINCI, Venus Life Finder) is needed across multiple cloud layers.