For nearly 50 years, Venus’s clouds have been understood as droplets of concentrated sulfuric acid—but a 2025 reinterpretation of data inadvertently collected by NASA’s Pioneer Venus Large Probe in 1978 suggests their aerosols may instead be about 60 per cent bound water by mass, locked largely inside hydrated iron and magnesium salts.

For nearly 50 years, Venus’s clouds have been understood as droplets of concentrated sulfuric acid—but a 2025 reinterpretation of data inadvertently collected by NASA’s Pioneer Venus Large Probe in 1978 suggests their aerosols may instead be about 60 per cent bound water by mass, locked largely inside hydrated iron and magnesium salts.

An accidental aerosol capture during Pioneer Venus's descent may have recorded hydrated salts and far more bound water than the standard sulphuric-acid cloud model allows.