What process is cited by new studies as causing rapid water loss on Venus, challenging the long-lived ocean theory?

Photodissociation by solar radiation

Recent scientific scrutiny of the 'wet past' scenario suggests it may be less likely due to evidence regarding atmospheric stability. Researchers modeling the evolution have focused on how quickly water vapor, a powerful greenhouse gas, would be removed from the upper atmosphere over billions of years when exposed to sunlight. The specific process identified is photodissociation, where sunlight breaks apart the atmospheric water molecules, allowing the lighter components to escape into space. This mechanism is significant enough that new studies argue against a long-lived surface ocean, suggesting water might have been lost much faster than previously modeled.