Venus, often deemed Earth's twin, presents a stark contrast in surface conditions that render it uninhabitable. Recent findings from ESA's Venus Express reveal an unexpected surge in the abundance of water molecule variants H2O and HDO in Venus' mesosphere, revolutionizing our understanding of the planet's water history. Despite Venus' current extreme temperatures and pressures, the study suggests that it might have harbored a water-rich environment in the past, comparable to Earth. Dr. Hiroki Karyu from Tohoku University highlights the divergent evolution of Venus and Earth, with Venus exhibiting extreme conditions unlike its sibling planet. The research delves into the deuterium to hydrogen ratio in Venus' atmosphere, indicating significant deuterium enrichment over time due to solar radiation processes. By analyzing data between 70 and 110 km altitude, the team found a substantial increase in H2O and HDO concentrations, with the HDO/H2O ratio showing a remarkable surge, surpassing levels in Earth's oceans. The study proposes a mechanism involving hydrated sulfuric acid aerosols to explain these observations, underscoring the role of altitude variations in deuterium and hydrogen reservoirs. The study's implications extend to understanding planetary habitability and water history, offering insights into preventing Earth from following Venus' inhospitable path. The researchers advocate for integrating altitude-dependent processes into models to enhance predictions about deuterium dynamics. Published in Proceedings of National Academy of Sciences, this research opens new avenues for unraveling Venus's mysteries and refining our knowledge of planetary evolution.